Excitation modulation frequency domain ultraviolet visible absorption spectrum testing system and method based on phase-locked amplifier and application of excitation modulation frequency domain ultraviolet visible absorption spectrum testing system and method

Abstract

The invention discloses an excitation modulation frequency domain ultraviolet visible absorption spectrum testing system and method based on a lock-in amplifier and application. The test system comprises an excitation modulation system, a spectrum acquisition system, a signal acquisition and analysis system and a LabView upper computer system, the spectrum acquisition system comprises a portable fiber optic spectrometer, and the signal acquisition and analysis system comprises a data acquisition card and a lock-in amplifier. According to the invention, a LabView program is utilized to carry out control and data acquisition and analysis on the system. Compared with the traditional in-situ ultraviolet-visible absorption spectrum, the in-situ ultraviolet-visible absorption spectrum based on the lock-in amplifier has the advantages that excellent signal resolution can be realized with higher time resolution, and the in-situ ultraviolet-visible absorption spectrum based on the lock-in amplifier is particularly suitable for some systems with higher reaction rate and trace concentration change. The test system and the test method are not only suitable for common electrochromic and photochromic materials, but also suitable for dynamic characterization of more catalytic materials.

Description

Technical Field

[0001] The invention relates to an excitation modulation frequency domain ultraviolet-visible absorption spectrum testing system, method and application based on a lock-in amplifier, belonging to the technical field of material characterization. Background Art

[0002] Some materials change color under external stimulation such as voltage or light due to reversible physical and chemical processes in the bulk or at the interface of the material. This phenomenon is called electrochromism or photochromism. In particular, some catalytic materials will form trace amounts of reaction intermediates on the surface during chemical reactions, which have different absorption responses from the main material. UV-visible spectroscopy characterization of these materials can not only evaluate material properties, but also study the mechanisms related to the physical and chemical processes of the materials.

[0003] In order to study the spectral response characteristics and differences of materials under different conditions, common testing methods usually involve obtaining differential absorption spectra by performing differential spectra under two excitation conditions (with / without, high / low). Although traditional grating spectrometers have a high signal-to-noise ratio, they are only suitable for steady-state testing and it is difficult to obtain kinetic information on the material time scale. Although transient absorption spectroscopy technology has excellent time resolution, its device is complex and costly. For this reason, it is necessary to develop a characterization technology with a simple structure and low cost.

[0004] The UV-visible absorption spectrum detection system based on a portable fiber optic spectrometer has higher acquisition efficiency and significant advantages in time resolution (usually as low as a few milliseconds), which is suitable for characterizing the response dynamics of various materials to external stimuli. At the same time, in order to restore the state of the material under working conditions as much as possible, the external excitation level should be as weak as possible, which brings challenges to differential signal detection. Current tests based on portable spectrometers usually require hundreds or thousands of averages to obtain a good quality spectrum, which greatly sacrifices its time resolution. Summary of the invention

[0005] The purpose of the present invention is: in view of the shortcomings of the prior art, the present invention provides an excitation modulated frequency domain ultraviolet-visible absorption spectrum test system, method and application based on a phase-locked amplifier. Specifically, the present invention provides a test scheme for measuring the frequency domain response of an absorption spectrum by modulating an external excitation - excitation modulated absorption spectroscopy (EMAS) measurement; according to the type of excitation, the present invention mainly involves light modulated absorption spectroscopy (LMAS) acquisition test and voltage modulated absorption spectroscopy (PMAS) acquisition test.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an excitation modulation frequency domain ultraviolet-visible absorption spectrum test system based on a phase-locked amplifier, comprising an excitation modulation system, a spectrum test system, a signal acquisition and analysis system, and a LabView host computer system; the excitation modulation system comprises a modulation voltage system and / or a modulation light intensity system, the spectrum acquisition system comprises a sample stage, a detection light source, an optical fiber, an optical fiber coupler, and a portable optical fiber spectrometer, the signal acquisition and analysis system comprises a data acquisition card and a phase-locked amplifier; the LabView host computer system comprises a computer and LabView host computer software;

[0008] The excitation modulation system, spectrum test system, and signal acquisition and analysis system are controlled by a LabView host computer system respectively;

[0009] The modulation voltage or the modulation light intensity emitted by the excitation modulation system is applied to the sample respectively, and the modulation signal of the excitation modulation system is output to the reference signal input terminal of the lock-in amplifier;

[0010] The detection light emitted by the detection light source is coupled to the optical fiber through the optical fiber coupler under the action of the modulation voltage or the modulation light and irradiates the sample on the sample stage. The transmitted light passing through the sample is coupled to the optical fiber through another optical fiber coupler and input into the portable optical fiber spectrometer. After the data collected by the portable optical fiber spectrometer is transmitted to the computer, the light intensity value of the pixel where the required detection light wavelength is located is extracted, the absorption value ΔA is obtained through the formula calculation and the specified magnification A is amplified, and then output to the phase-locked amplifier through the data acquisition card. Finally, the phase-locked amplifier returns the results collected by the data acquisition card to the computer and records and saves them.

[0011] The absorption value calculation formula is:

[0012]

[0013] Where A is the set magnification, c is the attenuation coefficient of the phase-locked amplifier at the modulation frequency, I is the real-time measured light intensity signal of the portable fiber optic spectrometer at the target wavelength, and I dark is the light intensity value of the dark reference spectrum at the target wavelength, and I0 is the light intensity value of the reference spectrum at the target wavelength.

[0014] The time resolution of the test system of the present invention depends on the sum of the time for the spectrometer signal to be transmitted to the computer and the integration time of the single spectrum test; for the spectrometer Avantes AvaSpec-ULS2048XL used in each embodiment of the present invention, the transmission time is 2.44ms, and the integration time is mostly tms, so the effective time resolution is 2.44+tms.

[0015] Preferably, the light intensity modulation system includes a wave function generator, an LED constant current driver and an LED lamp; the wave function generator generates a sinusoidal or square wave alternating current (AC) signal, which is output to the LED constant current driver and drives the LED lamp, so that the intensity of the excitation light fluctuates at a given AC frequency; another signal with the same frequency and phase generated by the wave function generator is directly output to the reference signal input terminal of the phase-locked amplifier.

[0016] Preferably, the modulation voltage system includes a function generator and a constant potentiostat / source meter; the wave function generator generates a sinusoidal or square wave alternating current (AC) signal, which is output to the constant potentiostat / source meter, so that the voltage applied to the sample fluctuates at a given AC frequency; another signal with the same frequency and phase generated by the wave function generator is directly output to the reference signal input terminal of the phase-locked amplifier.

[0017] Preferably, the detection light source is a tungsten halogen lamp.

[0018] Preferably, the LabView host computer software includes a LabView spectrum acquisition program, a LabView lock-in amplifier data acquisition program and a LabView wave function generation program. The LabView host computer system controls the parameter setting and spectrum acquisition of the spectrum test system through the LabView spectrum acquisition program, controls the parameter setting and signal acquisition of the lock-in amplifier through the LabView lock-in amplifier data acquisition program, and controls the parameter setting of the excitation modulation system through the LabView wave function generation program.

[0019] In a second aspect, the present invention provides a method for testing light intensity modulation ultraviolet-visible absorption spectra, using the test system described in the first aspect to collect light intensity modulation or voltage modulation ultraviolet-visible absorption spectra, including collecting absorption spectra within a specified ultraviolet-visible light wavelength range under a single excitation modulation frequency (wavelength measurement mode) and / or collecting a single ultraviolet-visible detection photoelectric absorption response within multiple excitation modulation frequency ranges (frequency measurement mode), the test method comprising the following steps:

[0020] Step 1: Turn on the connected test system and place the sample on the sample table;

[0021] Step 2: Adjust the light path, turn off the detection light source, and record the dark state background spectrum;

[0022] Step 3: Turn on the modulation voltage or light intensity by exciting the modulation system and wait for the system to stabilize;

[0023] Step 4: Turn on the detection light source and record the reference spectrum;

[0024] Step 5: Select the wavelength or frequency measurement mode, record and collect the spectral signal locked by the phase-locked amplifier, and complete the collection of the UV-visible absorption spectrum.

[0025] In some embodiments of the present invention, the collection of the light intensity modulation ultraviolet-visible absorption spectrum specifically comprises the following steps:

[0026] Step A1: Connect the wave function generator, lock-in amplifier, data acquisition card, and spectrometer to the USB port of the computer; turn on the wave function generator, lock-in amplifier, and computer;

[0027] Step A2: placing a sample on a sample stage;

[0028] Step A3: Connect the wave function generator signal channel 1 to the LED constant current driver, and the LED constant current driver to the LED lamp; adjust the optical path so that the LED light spot is irradiated on the sample surface; connect the wave function generator signal channel 2 to the reference signal input of the phase-locked amplifier; connect the halogen tungsten lamp output optical fiber to the optical fiber coupler, and adjust the optical path so that the detection light spot coincides with the LED light spot; place another optical fiber coupler on the back side of the sample and connect it to the spectrometer through the optical fiber. Connect the analog output signal of the data acquisition card to the phase-locked amplifier;

[0029] Step A4: In the LabView spectrum acquisition program, set the spectrometer measurement parameters according to the characteristics of the sample to be measured, and run the LabView spectrum acquisition program; open the constant potential instrument / source meter as needed and connect the sample or electrolytic cell, set the constant voltage value and run; click "Start Measurement" to start spectrum acquisition, adjust the optical path and integration time; close the halogen tungsten lamp shutter, and click "Dark" to record the dark state background spectrum; set the parameters of the two signal channels of the wave function generator and output them, so that the LED light intensity is modulated according to the specified function; after the system is stable and the phase-locked amplifier correctly detects the modulation frequency, open the halogen tungsten lamp shutter, and click "Light" to record the reference spectrum; set the detection light wavelength in the program;

[0030] Step A5: Set the measurement parameters of the phase-locked amplifier and the data export path according to the actual situation, select the wavelength measurement mode or the frequency measurement mode in the measurement mode, and run the LabView phase-locked amplifier data acquisition program; when the phase-locked amplifier correctly locks the signal, click "Record" and switch to the next target wavelength or frequency to be measured in the LabView spectrum acquisition program; repeat this step until the required spectral range is acquired.

[0031] In some embodiments of the present invention, the acquisition of the voltage-modulated ultraviolet-visible absorption spectrum specifically comprises the following steps:

[0032] Step B1: Connect the wave function generator, lock-in amplifier, data acquisition card, and spectrometer to the USB port of the computer; turn on the wave function generator, lock-in amplifier, and computer;

[0033] Step B2: placing a sample on a sample stage;

[0034] Step B3: Connect the signal channel 1 of the wave function generator to the constant potential meter / source meter; connect the signal channel 2 of the wave function generator to the reference signal input terminal of the phase-locked amplifier; connect the output optical fiber of the halogen tungsten lamp to the optical fiber coupler, and adjust the optical path so that the detection light spot is irradiated on the sample surface; place another optical fiber coupler on the back side of the sample and connect it to the spectrometer through the optical fiber; connect the analog output signal of the data acquisition card to the phase-locked amplifier;

[0035] Step B4: In the LabView spectrum acquisition program, set the spectrometer measurement parameters according to the characteristics of the sample to be measured, and run the LabView spectrum acquisition program; click "Start Measurement" to start spectrum acquisition, adjust the optical path and integration time; close the halogen tungsten lamp shutter, and click "Dark" to record the dark state background spectrum; set the parameters of the two signal channels of the wave function generator and output them, so that the LED light intensity is modulated according to the specified function; after the system is stable and the phase-locked amplifier correctly detects the modulation frequency, open the halogen tungsten lamp shutter, and click "Light" to record the reference spectrum; set the detection light wavelength in the program;

[0036] Step B5: Set the measurement parameters of the phase-locked amplifier and the data export path according to the actual situation, select the wavelength measurement mode or the frequency measurement mode in the measurement mode, and run the LabView phase-locked amplifier data acquisition program; when the phase-locked amplifier correctly locks the signal, click "Record" and switch to the next target wavelength or frequency to be measured in the LabView spectrum acquisition program; repeat this step until the required spectral range is acquired.

[0037] In a third aspect, the present invention further provides an application of the test system described in the first aspect and the test method described in the second aspect, wherein the application is selected from any one of the following applications:

[0038] 1) Application in UV absorption spectroscopy for dynamic characterization of materials;

[0039] 2) Application in characterizing and identifying intermediate species produced when catalytic materials undergo chemical reactions;

[0040] 3) Application in research and evaluation of material properties;

[0041] 4) Application in studying the mechanisms related to the physical and chemical processes of materials;

[0042] The materials include electrochromic materials, photochromic materials, and catalytic materials. The catalytic materials include photocatalytic materials, electrocatalytic materials, and photoelectrocatalytic materials.

[0043] Preferably, the dynamic characterization includes dynamic characterization during a chemical reaction.

[0044] In some application embodiments of the present invention, the testing system and method are used to characterize different chemical reactions of electrochemically active materials under different external bias conditions, and to characterize and identify different intermediate species produced in the chemical reactions.

[0045] In some other application embodiments of the present invention, the catalytic performance of two materials is comparatively evaluated by using the test system and method.

[0046] The present invention provides an excitation modulation frequency domain ultraviolet-visible absorption spectrum testing system and method based on a portable spectrometer. With the help of a lock-in amplifier, compared with the traditional in-situ ultraviolet-visible absorption spectrum, it achieves excellent signal resolution (0.01mΔO.D.) with a higher time resolution (about 2.5ms), which is particularly suitable for some systems with faster reaction rates and trace concentration changes. The test scheme of the present invention helps to explore the photochromic, electrochromic, and catalytic reaction kinetics information under different excitation modulation frequencies.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The present invention provides an excitation modulation frequency domain ultraviolet visible absorption spectrum testing system and method based on a phase-locked amplifier, which can achieve high signal resolution and time resolution to measure material absorption changes at a relatively low cost, and use the photosensitive element array of a portable fiber optic spectrometer as a photodetector to achieve differential spectrum acquisition of electrochromic and photochromic phenomena; the phase-locked amplifier can also be used to collect and analyze the absorption signal changes of a single wavelength at different frequencies;

[0049] (2) The present invention utilizes a phase-locked amplification algorithm to fully utilize the time resolution capability of the spectrometer and simultaneously remove drift caused by the instrument or the environment, thereby greatly improving signal resolution. The testing system and method of the present invention are not only applicable to common electrochromic and photochromic materials, but also to the dynamic characterization of a variety of catalytic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of the testing principle of Light Intensity Modulation Frequency Domain UV-Vis Absorption Spectroscopy (LMAS);

[0051] Figure 2 This is a schematic diagram of the test principle of voltage modulation frequency domain ultraviolet visible absorption spectroscopy (PMAS);

[0052] Figure 3 This is the flow chart of the test operation of the excitation modulation frequency domain UV-visible absorption spectrum;

[0053] Figure 4 It is the LabView spectrum acquisition program operation interface-1;

[0054] Figure 5 It is the LabView spectrum acquisition program operation interface-2;

[0055] Figure 6 It is the interface of LabView lock-in amplifier data acquisition program;

[0056] Figure 7 It is the interface of LabView wave function generator program;

[0057] Figure 8 The wavelength domain PMAS test results of α-Fe2O3 thin film samples in two voltage modulation ranges;

[0058] Fig. 9 The wavelength domain LMAS test results of α-Fe2O3 film samples at 0.6VHg / HgO;

[0059] Fig.10 For α-Fe2O3 thin film samples at 0.6V Hg / HgO LMAS test results under no light intensity modulation (gray) and 0.5Hz light intensity modulation (red); 10 data points were recorded under the two test conditions, and the standard deviation was less than 0.01mΔO.D.;

[0060] Fig.11 NiFeO x Wavelength domain PMAS test results under two voltage modulation intervals;

[0061] Fig.12 NiFeO x Frequency domain PMAS test results at 650nm under two voltage modulation intervals. DETAILED DESCRIPTION

[0062] In order to make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0063] Example 1: Light intensity modulation UV-visible absorption spectrum measurement

[0064] This embodiment provides a system and method for testing light intensity modulation ultraviolet visible absorption spectrum. The testing principle is as follows: Figure 1 As shown: The wave function generator generates a sinusoidal or square wave alternating current (AC) signal disturbance, which is output to the LED constant current driver and drives the LED lamp, so that the intensity of the excitation light fluctuates at a given AC frequency. Another signal with the same frequency and phase generated by the wave function generator is directly output to the reference signal input of the phase-locked amplifier. The halogen tungsten lamp is used as the detection light source, and its light spot is irradiated on the sample. The transmitted light through the sample is coupled to the optical fiber and input into the portable fiber optic spectrometer. After the spectrometer data is transmitted to the computer, the pixel intensity value of the required detection light wavelength is extracted, and the absorption value ΔA is obtained through the formula calculation and amplified by the specified magnification A, and then output to the phase-locked amplifier through the data acquisition card. Finally, the results of the phase-locked amplifier are returned to the computer in real time and recorded. The specific test steps are as follows:

[0065] (I) Wavelength domain measurement

[0066] 1. Turn on the halogen tungsten lamp and preheat for 15 minutes. Connect the wave function generator, lock-in amplifier, data acquisition card, and spectrometer to the computer USB port. Turn on the wave function generator, lock-in amplifier, and computer.

[0067] 2. Place the sample on the sample stage.

[0068] 3. Connect the wave function generator signal channel 1 to the LED constant current driver, which is connected to the LED lamp. Adjust the optical path so that the LED light spot is irradiated on the sample surface. Connect the wave function generator signal channel 2 to the reference signal input of the phase-locked amplifier. Connect the halogen tungsten lamp output fiber to the fiber coupler, and adjust the optical path so that the detection light spot coincides with the LED light spot. Place another fiber coupler on the back side of the sample and connect it to the spectrometer through the optical fiber. Connect the analog output signal of the data acquisition card to the phase-locked amplifier.

[0069] 4. Set the spectrometer measurement parameters according to the actual situation in the LabView spectrum acquisition program, and run the LabView spectrum acquisition program. Open the potentiostat / source meter as needed and connect the sample or electrolytic cell, set the voltage value and run. Click "Start Measurement" to start collecting the spectrum, adjust the optical path and integration time so that the maximum spectrum intensity is close to but not higher than 65500. Close the halogen tungsten lamp shutter and click "Dark" to record the dark state background spectrum. Set the parameters of the two signal channels of the wave function generator and output them so that the LED light intensity is modulated according to the specified function. After the system is stable and the phase-locked amplifier correctly detects the modulation frequency, open the halogen tungsten lamp shutter and click "Light" to record the reference spectrum. Set the detection light wavelength in the program.

[0070] 5. Set the lock-in amplifier measurement parameters and data export path according to the actual situation, select "Spectrum" in the measurement mode column, set the wavelength step in "Step", and run the LabView lock-in amplifier data acquisition program.

[0071] 6. When the phase-locked amplifier has correctly locked the signal, click "Record" to switch to the next target detection light wavelength in the LabView spectrum acquisition program. Repeat this step until the desired spectral range is acquired.

[0072] 7. Click "EXIT AVS" to exit in the LabView spectrum acquisition program, and click "Terminate" to exit in the LabView lock-in amplifier data acquisition program.

[0073] (II) Frequency domain measurement

[0074] 1. Turn on the halogen tungsten lamp and preheat for 15 minutes. Connect the wave function generator, lock-in amplifier, data acquisition card, and spectrometer to the computer USB port. Turn on the wave function generator, lock-in amplifier, and computer.

[0075] 2. Place the sample on the sample stage.

[0076] 3. Connect the wave function generator signal channel 1 to the LED constant current driver, which is connected to the LED lamp. Adjust the optical path so that the LED light spot is irradiated on the sample surface. Connect the wave function generator signal channel 2 to the reference signal input of the phase-locked amplifier. Connect the halogen tungsten lamp output fiber to the fiber coupler, and adjust the optical path so that the detection light spot coincides with the LED light spot. Place another fiber coupler on the back side of the sample and connect it to the spectrometer through the optical fiber. Connect the analog output signal of the data acquisition card to the phase-locked amplifier.

[0077] 4. Set the spectrometer measurement parameters according to the actual situation in the LabView spectrum acquisition program, and run the LabView spectrum acquisition program. Open the potentiostat / source meter as needed and connect the sample or electrolytic cell, set the voltage value and run. Click "Start Measurement" to start collecting the spectrum, adjust the optical path and integration time so that the maximum spectrum intensity is close to but not higher than 65500. Close the halogen tungsten lamp shutter and click "Dark" to record the dark state background spectrum. Set the parameters of the two signal channels of the wave function generator and output them so that the LED light intensity is modulated according to the specified function. After the system is stable and the phase-locked amplifier correctly detects the modulation frequency, open the halogen tungsten lamp shutter and click "Light" to record the reference spectrum. Set the detection light wavelength in the program.

[0078] 5. Set the lock-in amplifier measurement parameters and data export path according to the actual situation, select "Nyquist" in the measurement mode column, and run the LabView lock-in amplifier data acquisition program.

[0079] 6. When the phase-locked amplifier has locked onto the signal correctly, click "Record" to switch to the next target modulation frequency in the LabView wave function generator. Repeat this step until the desired frequency range is acquired.

[0080] 7. Click "EXIT AVS" to exit in the LabView spectrum acquisition program, and click "Terminate" to exit in the LabView lock-in amplifier data acquisition program.

[0081] Example 2: Voltage-modulated UV-visible absorption spectrum measurement

[0082] This embodiment provides a voltage modulation ultraviolet visible absorption spectrum testing system and method, the testing principle is as follows Figure 2As shown: The wave function generator generates a sinusoidal or square wave alternating current (AC) signal disturbance, which is output to the constant potential instrument / source meter, so that the voltage applied to the sample fluctuates at a given AC frequency. Another signal with the same frequency and phase generated by the wave function generator is directly output to the reference signal input of the phase-locked amplifier. A halogen tungsten lamp is used as the detection light source, and its light spot is irradiated on the sample. The transmitted light through the sample is coupled to the optical fiber and input into the portable fiber optic spectrometer. After the spectrometer data is transmitted to the computer, the pixel intensity value of the required detection light wavelength is extracted, and the absorption value ΔA is obtained through the formula calculation and amplified by the specified magnification A, and then output to the phase-locked amplifier through the data acquisition card. Finally, the results of the phase-locked amplifier are returned to the computer in real time and recorded. The specific test steps are as follows:

[0083] (I) Wavelength domain measurement

[0084] 1. Turn on the halogen tungsten lamp and preheat for 15 minutes. Connect the wave function generator, lock-in amplifier, data acquisition card, and spectrometer to the computer USB port. Turn on the wave function generator, lock-in amplifier, and computer.

[0085] 2. Place the sample on the sample stage.

[0086] 3. Connect the wave function generator signal channel 1 to the potentiostat / source meter. Connect the wave function generator signal channel 2 to the reference signal input of the lock-in amplifier. Connect the halogen tungsten lamp output fiber to the fiber coupler, and adjust the optical path so that the detection light spot is irradiated on the sample surface. Place another fiber coupler on the back side of the sample and connect it to the spectrometer through the optical fiber. Connect the analog output signal of the data acquisition card to the lock-in amplifier.

[0087] 4. Set the spectrometer measurement parameters according to the actual situation in the LabView spectrum acquisition program, and run the LabView spectrum acquisition program. Click "Start Measurement" to start collecting spectra, adjust the optical path and integration time so that the maximum spectrum intensity is close to but not higher than 65500. Close the halogen tungsten lamp shutter, and click "Dark" to record the dark state background spectrum. Set the parameters of the two signal channels of the wave function generator and output them so that the voltage applied to the sample is modulated according to the specified function. After the system is stable and the phase-locked amplifier correctly detects the modulation frequency, open the halogen tungsten lamp shutter and click "Light" to record the reference spectrum. Set the detection light wavelength in the program.

[0088] 5. Set the lock-in amplifier measurement parameters and data export path according to the actual situation, select "Spectrum" in the measurement mode column, set the wavelength step in "Step", and run the LabView lock-in amplifier data acquisition program.

[0089] 6. When the phase-locked amplifier has correctly locked the signal, click "Record" to switch to the next target detection light wavelength in the LabView spectrum acquisition program. Repeat this step until the desired spectral range is acquired.

[0090] 7. Click "EXIT AVS" to exit in the LabView spectrum acquisition program, and click "Terminate" to exit in the LabView lock-in amplifier data acquisition program.

[0091] (II) Frequency domain measurement

[0092] 1. Turn on the halogen tungsten lamp and preheat for 15 minutes. Connect the wave function generator, lock-in amplifier, data acquisition card, and spectrometer to the computer USB port. Turn on the wave function generator, lock-in amplifier, and computer.

[0093] 2. Place the sample on the sample stage.

[0094] 3. Connect the wave function generator signal channel 1 to the potentiostat / source meter. Connect the wave function generator signal channel 2 to the reference signal input of the lock-in amplifier. Connect the halogen tungsten lamp output fiber to the fiber coupler, and adjust the optical path so that the detection light spot is irradiated on the sample surface. Place another fiber coupler on the back side of the sample and connect it to the spectrometer through the optical fiber. Connect the analog output signal of the data acquisition card to the lock-in amplifier.

[0095] 4. Set the spectrometer measurement parameters according to the actual situation in the LabView spectrum acquisition program, and run the LabView spectrum acquisition program. Click "Start Measurement" to start collecting spectra, adjust the optical path and integration time so that the maximum spectrum intensity is close to but not higher than 65500. Close the halogen tungsten lamp shutter, and click "Dark" to record the dark state background spectrum. Set the parameters of the two signal channels of the wave function generator and output them so that the voltage applied to the sample is modulated according to the specified function. After the system is stable and the phase-locked amplifier correctly detects the modulation frequency, open the halogen tungsten lamp shutter and click "Light" to record the reference spectrum. Set the detection light wavelength in the program.

[0096] 5. Set the lock-in amplifier measurement parameters and data export path according to the actual situation, select "Nyquist" in the measurement mode column, and run the LabView lock-in amplifier data acquisition program.

[0097] 6. When the phase-locked amplifier has locked onto the signal correctly, click "Record" to switch to the next target modulation frequency in the LabView wave function generator. Repeat this step until the desired frequency range is acquired.

[0098] 7. Click "EXIT AVS" to exit in the LabView spectrum acquisition program, and click "Terminate" to exit in the LabView lock-in amplifier data acquisition program.

[0099] The above test operation process is as follows Figure 3 The LabView spectrum acquisition program operation interface is as follows. Figure 4 , Figure 5 As shown, the LabView lock-in amplifier data acquisition program interface is as follows Figure 6 As shown, the LabView wave function generation program interface is as follows Figure 7 shown.

[0100] Application Example 1

[0101] Electrochemically active materials will undergo different chemical reactions under different external bias conditions. To demonstrate this process, in this example, a hematite α-Fe2O3 film is loaded on a transparent conductive glass substrate and fixed on a working electrode clip. The voltage window of the sample and the reference electrode in a three-electrode electrolytic cell system (working electrode: sample; reference electrode: Hg / HgO; counter electrode: platinum wire; electrolyte: 1M KOH) is modulated by a potentiostat, and the voltage-modulated UV-visible absorption spectrum response of α-Fe2O3 is recorded. Figure 8 As shown, when the voltage is between -0.2 and 0.6V Hg / HgO When the interval is modulated, the voltage is between 0.6 and 0.8V. Hg / HgO The absorption spectrum response is significantly different when the range is modulated. Therefore, two different chemical species can be distinguished. In particular, for 0.6 to 0.8V Hg / HgO The signal generated by interval modulation, combined with its electrochemical characteristics, can be identified as an intermediate species in electrocatalytic water oxidation.

[0102] Application Example 2

[0103] When the α-Fe2O3 film sample described in Example 1 is placed in an electrolytic cell at 0.6V Hg / HgO When exposed to light at a constant voltage, a photocurrent caused by water oxidation reaction can be generated. Therefore, this embodiment performs a light intensity modulation UV-visible absorption spectrum test at this voltage. Fig. 9 As shown in the test results, its spectral response characteristics are similar to those of the α-Fe2O3 film sample in Application Example 1 under dark conditions by voltage modulation (0.6 to 0.8V Hg / HgO ) UV-visible absorption spectrum response is similar. Fig.10 As shown, under two different lighting conditions (with modulation / without modulation), based on the calculation results of the standard deviation of the real test data, it is concluded that the test resolution of LMAS is better than 0.01mΔO.D.

[0104] Application Example 3

[0105] Transition metal oxides such as NiO x It is a common inorganic electrochromic material. This type of compound is also often used as a catalyst in the electrocatalytic decomposition of water and oxygen evolution reaction. x Doped with Fe to form NiFeO x When the material is measured by voltammetry, two oxidation processes can be distinguished, so it can be inferred that it has two intermediate species of water-resolving oxygen reaction. When the wavelength domain voltage modulation UV-visible absorption spectrum is used in two voltage modulation intervals (0.52 to 0.54V Hg / HgO and 0.60 to 0.62V Hg / HgO ) test, it was found that the absorption spectra of the two were very similar (such as Fig.11 Therefore, it is difficult to distinguish them. Therefore, this embodiment carries out frequency domain voltage modulation ultraviolet visible absorption spectroscopy. When the frequency range is selected as 60Hz to 0.2Hz, as shown in Fig.12 As shown, the data presents a semicircle in the Nyquist plot. The lowest point is obtained by fitting and the characteristic angular frequency characteristic value is obtained: between 0.52 and 0.54V Hg / HgO The modulation interval is 14.1s -1 , at 0.60 to 0.62V Hg / HgO The modulation interval is 42.5s -1 , thus successfully distinguishing the two through kinetic parameters.

[0106] The above description is only a preferred embodiment of the present invention and is not any formal or substantial limitation of the present invention. It should be pointed out that a person skilled in the art can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. An excitation modulation frequency domain ultraviolet visible absorption spectrum test system based on a lock-in amplifier, characterized in that: It includes an excitation modulation system, a spectrum test system, a signal acquisition and analysis system, and a LabView host computer system; the excitation modulation system includes a modulation voltage system and / or a modulation light intensity system, the spectrum acquisition system includes a sample stage, a detection light source, an optical fiber, an optical fiber coupler, and a portable optical fiber spectrometer, the signal acquisition and analysis system includes a data acquisition card and a phase-locked amplifier; the LabView host computer system includes a computer and LabView host computer software; The excitation modulation system, spectrum test system, and signal acquisition and analysis system are respectively controlled by a LabView host computer system; The modulation voltage or the modulation light intensity emitted by the excitation modulation system is applied to the sample to be tested, and the modulation signal of the excitation modulation system is output to the reference signal input terminal of the lock-in amplifier; The detection light emitted by the detection light source is coupled to the optical fiber through the optical fiber coupler under the action of the modulated voltage or modulated light and irradiated on the sample on the sample stage. The transmitted light passing through the sample is coupled to the optical fiber through another optical fiber coupler and input into the portable optical fiber spectrometer. After the data collected by the portable optical fiber spectrometer is transmitted to the computer, the pixel light intensity value of the required detection light wavelength is extracted, the absorption value ΔA is obtained through the formula calculation and the specified magnification A is amplified, and then output to the phase-locked amplifier through the data acquisition card. Finally, the phase-locked amplifier returns the results collected by the data acquisition card to the computer and records and saves them. The absorption value calculation formula is: Where A is the set magnification, c is the attenuation coefficient of the phase-locked amplifier at the modulation frequency, I is the real-time measured light intensity signal of the portable fiber optic spectrometer at the target wavelength, and I dark is the light intensity value of the dark reference spectrum at the target wavelength, and I0 is the light intensity value of the reference spectrum at the target wavelength.

2. The excitation modulation frequency domain ultraviolet visible absorption spectrum testing system according to claim 1, characterized in that: The light intensity modulation system includes a wave function generator, an LED constant current driver and an LED lamp; the wave function generator generates a sinusoidal or square wave alternating current (AC) signal, which is output to the LED constant current driver and drives the LED lamp, so that the light intensity of the excitation light fluctuates at a given AC frequency; another signal with the same frequency and phase generated by the wave function generator is directly output to the reference signal input end of the phase-locked amplifier.

3. The excitation modulation frequency domain ultraviolet visible absorption spectrum testing system according to claim 1, characterized in that: The modulation voltage system includes a function generator and a constant potential meter / source meter; the wave function generator generates a sinusoidal or square wave alternating current (AC) signal, which is output to the constant potential meter / source meter, so that the voltage applied to the sample fluctuates at a given AC frequency; another signal with the same frequency and phase generated by the wave function generator is directly output to the reference signal input terminal of the lock-in amplifier.

4. The excitation modulation frequency domain ultraviolet visible absorption spectrum testing system according to claim 1, characterized in that: The detection light source is a tungsten halogen lamp.

5. The excitation modulation frequency domain ultraviolet visible absorption spectrum testing system according to claim 1, characterized in that: The LabView host computer software includes a LabView spectrum acquisition program, a LabView lock-in amplifier data acquisition program and a LabView wave function generation program. The LabView host computer system controls the parameter setting and spectrum acquisition of the spectrum test system through the LabView spectrum acquisition program, controls the parameter setting and signal acquisition of the lock-in amplifier through the LabView lock-in amplifier data acquisition program, and controls the parameter setting of the excitation modulation system through the LabView wave function generation program.

6. A light intensity modulation ultraviolet visible absorption spectrum testing method, characterized in that: The test system described in any one of claims 1 to 4 is used to collect light intensity modulation or voltage modulation ultraviolet-visible absorption spectra, including collecting absorption spectra within a specified ultraviolet-visible light wavelength range under a single excitation modulation frequency (wavelength measurement mode) and / or collecting a single ultraviolet-visible detection photoelectric absorption response within multiple excitation modulation frequency ranges (frequency measurement mode), and the test method comprises the following steps: Step 1: Turn on the connected test system and place the sample on the sample table; Step 2: Adjust the light path, turn off the detection light source, and record the dark state background spectrum; Step 3: Turn on the modulation voltage or light intensity by exciting the modulation system and wait for the system to stabilize; Step 4: Turn on the detection light source and record the reference spectrum; Step 5: Select the wavelength or frequency measurement mode, record and collect the spectral signal locked by the phase-locked amplifier, and complete the collection of the UV-visible absorption spectrum.

7. The testing method according to claim 6, characterized in that: The collection of the light intensity modulation ultraviolet-visible absorption spectrum specifically includes the following steps: Step A1: Connect the wave function generator, lock-in amplifier, data acquisition card, and spectrometer to the USB port of the computer; turn on the wave function generator, lock-in amplifier, and computer; Step A2: placing a sample on a sample stage; Step A3: Connect the wave function generator signal channel 1 to the LED constant current driver, and the LED constant current driver to the LED lamp; adjust the optical path so that the LED light spot is irradiated on the sample surface; connect the wave function generator signal channel 2 to the reference signal input of the phase-locked amplifier; connect the halogen tungsten lamp output optical fiber to the optical fiber coupler, and adjust the optical path so that the detection light spot coincides with the LED light spot; place another optical fiber coupler on the back side of the sample and connect it to the spectrometer through the optical fiber. Connect the analog output signal of the data acquisition card to the phase-locked amplifier; Step A4: In the LabView spectrum acquisition program, set the spectrometer measurement parameters according to the characteristics of the sample to be measured, and run the LabView spectrum acquisition program; open the constant potential instrument / source meter as needed and connect the sample or electrolytic cell, set the constant voltage value and run; click "Start Measurement" to start spectrum acquisition, adjust the optical path and integration time; close the halogen tungsten lamp shutter, and click "Dark" to record the dark state background spectrum; set the parameters of the two signal channels of the wave function generator and output them so that the LED light intensity is modulated according to the specified function; after the system is stable and the phase-locked amplifier correctly detects the modulation frequency, open the halogen tungsten lamp shutter, and click "Light" to record the reference spectrum; set the detection light wavelength in the program; Step A5: Set the measurement parameters of the phase-locked amplifier and the data export path according to the actual situation, select the wavelength measurement mode or frequency measurement mode in the measurement mode, and run the LabView phase-locked amplifier data acquisition program; when the phase-locked amplifier correctly locks the signal, click "Record" to switch to the next target wavelength or frequency to be measured in the LabView spectrum acquisition program; repeat this step until the required spectral range is acquired.

8. The testing method according to claim 6, characterized in that: The acquisition of the voltage-modulated ultraviolet-visible absorption spectrum specifically comprises the following steps: Step B1: Connect the wave function generator, lock-in amplifier, data acquisition card, and spectrometer to the USB port of the computer; turn on the wave function generator, lock-in amplifier, and computer; Step B2: placing a sample on a sample stage; Step B3: Connect the signal channel 1 of the wave function generator to the constant potential meter / source meter; connect the signal channel 2 of the wave function generator to the reference signal input terminal of the phase-locked amplifier; connect the output optical fiber of the halogen tungsten lamp to the optical fiber coupler, and adjust the optical path so that the detection light spot is irradiated on the sample surface; place another optical fiber coupler on the back side of the sample and connect it to the spectrometer through the optical fiber; connect the analog output signal of the data acquisition card to the phase-locked amplifier; Step B4: In the LabView spectrum acquisition program, set the spectrometer measurement parameters according to the characteristics of the sample to be measured, and run the LabView spectrum acquisition program; click "Start Measurement" to start spectrum acquisition, adjust the optical path and integration time; close the halogen tungsten lamp shutter, and click "Dark" to record the dark state background spectrum; set the parameters of the two signal channels of the wave function generator and output them so that the LED light intensity is modulated according to the specified function; after the system is stable and the phase-locked amplifier correctly detects the modulation frequency, open the halogen tungsten lamp shutter, and click "Light" to record the reference spectrum; set the detection light wavelength in the program; Step B5: Set the measurement parameters of the phase-locked amplifier and the data export path according to the actual situation, select the wavelength measurement mode or the frequency measurement mode in the measurement mode, and run the LabView phase-locked amplifier data acquisition program; when the phase-locked amplifier correctly locks the signal, click "Record" to switch to the next target wavelength or frequency to be measured in the LabView spectrum acquisition program; repeat this step until the required spectral range is acquired.

9. The test system according to any one of claims 1 to 5, and the use of the test method according to any one of claims 6 to 8, characterized in that: The application is selected from any one of the following applications: 1) Application in UV absorption spectroscopy for dynamic characterization of materials; 2) Application in characterizing and identifying intermediate species produced when catalytic materials undergo chemical reactions; 3) Application in research and evaluation of material properties; 4) Application in studying the mechanisms related to the physical and chemical processes of materials; The materials include electrochromic materials, photochromic materials, and catalytic materials.

10. The use according to claim 9, characterized in that: The dynamic characterization includes the dynamic characterization during a chemical reaction.

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