Phosphorus mixed anion compound crystal containing d10 transition metal and preparation method and application thereof

Abstract

The invention discloses a d10 transition metal-containing phosphorus mixed anion compound crystal as well as a preparation method and application thereof, and belongs to the technical field of infrared second-order nonlinear optical crystal materials. The chemical formula of the d10 transition metal-containing phosphorus mixed anion compound crystal is AM4PnX6, wherein A is selected from one of Cs, Rb, K, Na and Li; m is selected from one of Hg, Cd and Zn elements; pn is selected from one of P, As and Sb; x is selected from one of Cl, Br and I. The NLO effect of the crystal is 29.6-52.3 times that of commercial AgGaS2, phase matching is met, the laser damage threshold is 8.6-15.3 times that of the commercial AgGaS2, the band gap value is 2.4-3.3 eV, the powder infrared transmission range is 0.4-25.0 microns, and the crystal has excellent infrared nonlinear optical performance and is a novel infrared nonlinear optical material.

Description

Technical Field

[0001] This application relates to a 10 The invention discloses a transition metal phosphorus mixed anion compound crystal and a preparation method and application thereof, belonging to the technical field of infrared second-order nonlinear optical crystal materials. Background Art

[0002] In recent years, infrared nonlinear optical crystals (NLO) have attracted widespread attention due to their applications in generating mid- and far-infrared tunable lasers through second harmonic generation and cascade frequency conversion. At the same time, with the continuous development of technology, the demand for the wavelength application range of laser self-frequency doubling crystals and frequency doubling crystals, as well as the frequency doubling effect, is increasing. At present, the lasers in special bands in practical applications are obtained by frequency conversion of fundamental frequency lasers through frequency doubling crystals. Although practically applied frequency doubling crystal materials such as LiB3O5 (LBO), β-BaB2O4 (β-BBO), KH2PO4 (KDP), KTiOPO4 (KTP), AgGaS2 (AGS) and ZnGeP2 (ZGP) have made great progress in crystal growth, processing and application, the above crystals still cannot meet the needs of scientific and technological development. Up to now, commercial infrared NLO crystals AgGaS2, AgGaSe2 and ZnGeP2 have a large second harmonic generation (SHG) effect due to their chalcopyrite structure that is conducive to NLO. Therefore, the design and synthesis of novel IR-NLO materials with a balance of large SHG effect (>1×AGS) and moderate band gap (preferably >2.33 eV to avoid two-photon absorption of 1064 nm laser) are very important in the field of nonlinear optics. Summary of the invention

[0003] In order to provide a novel mid-to-far infrared nonlinear optical crystal that balances a medium band gap and a large SHG effect, the present application provides a series of d 10 Transition metal pnictium mixed anion compound crystals can greatly improve the disadvantage of narrow band gap of pnictium compounds by introducing halogens into pnictium compounds, while retaining the inherent advantage of strong SHG signal of pnictium compounds.

[0004] This application adopts the following technical solutions:

[0005] According to a first aspect of the present application, there is provided a 10 Transition metal phosphorus mixed anion compound crystal, the d 10 The unique crystal formula of transition metal phosphorus mixed anion compound is AM4PnX6;

[0006] Wherein, A is selected from one of Cs, Rb, K, Na, and Li;

[0007] M is selected from one of the elements Hg, Cd and Zn;

[0008] Pn is selected from one of P, As and Sb;

[0009] X is selected from one of Cl, Br and I.

[0010] Optionally, the 10 The crystals of transition metal phosphorus mixed anion compounds belong to the monoclinic system and the space group is Pm.

[0011] Optionally, the 10 The unit cell parameters of transition metal phosphorus mixed anion compound crystals are: α=90°, β=90°, γ=90-91°, Z=1.

[0012] Optionally, the 10 Transition metal phosphorus mixed anion compound crystals are host-guest compounds with non-centrosymmetric structures.

[0013] The main part of the host-guest is centered on the M atom, each M atom is coordinated with 3 X atoms and 1 Pn atom to form a [MPnX3] tetrahedral unit, every 3 [MPnX3] are connected at the top by Pn atoms to form a planar triangular trimer, the top of the trimer is connected to 1 [MPnX3] by sharing X atoms, the above 4 [MPnX3] tetrahedrons together form a T2 supertetrahedron, several of the T2 supertetrahedrons are connected end to end to form a three-dimensional channel-shaped 3D Cd-P / I main framework, the shape of the channel cross-section is approximately an equilateral triangle and is composed of 6 [MPnX3] tetrahedrons;

[0014] A + As a guest part, it is filled in the three-dimensional pore structure.

[0015] Optionally, the 10 The transition metal phosphorus mixed anion compound crystal has at least one of the following properties:

[0016] (1) The frequency multiplication factor is 29.6-52.3 times that of AGS, and both are phase matched;

[0017] (2) The laser damage threshold is 8.6-15.3 times that of AgGaS2;

[0018] (3) Band gap value is 2.4-3.3eV;

[0019] (4) The infrared transmittance range of the powder is 0.4-25.0 μm.

[0020] According to the first aspect of the present application, there is provided a 10 The method for preparing the transition metal phosphorus mixed anion compound crystal comprises the following steps:

[0021] A mixture including an A source, an M source, a Pn source, and an X source is placed under vacuum conditions, heated for reaction, and cooled to obtain the d-containing 10 Crystals of transition metal phosphorus mixed anion compounds.

[0022] Optionally, in the mixture, the element molar ratio of A, M, Pn and X is (1-4): (1-4): (1-2): (2-9).

[0023] Preferably, the A source is selected from AX;

[0024] The M source is selected from at least one of M element, M3Pn2, and MX2;

[0025] The Pn source is selected from at least one of Pn element and M3Pn2;

[0026] The X source is selected from at least one of MX2 and AX.

[0027] Optionally, the conditions for the heating reaction include: heating to 300-900°C at a rate of 30-50°C / h, and then keeping the temperature for 24 to 72 hours.

[0028] Optionally, the vacuum condition includes a vacuum degree of 10 -1 -10 -2 Pa.

[0029] Optionally, the cooling conditions include: cooling to 300° C. at a rate of 1-10° C. / h and then naturally cooling to room temperature.

[0030] According to the third aspect of the present application, there is provided a 10 Transition metal phosphorus mixed anion compound crystal or any one of the above preparation methods obtained containing d 10 The application of transition metal phosphorus mixed anion compound crystals as infrared nonlinear optical materials in the optical field.

[0031] The beneficial effects of this application include:

[0032] This application provides 10The NLO effect of the transition metal phosphorus mixed anion compound crystal is 29.6-52.3 times that of commercial AgGaS2, satisfying a type of phase matching; the laser damage threshold is 8.6-15.3 times that of commercial AgGaS2; the band gap value is 2.4-3.3eV; the infrared transmittance range of the powder is 0.4-25.0μm. This series of compounds has excellent infrared nonlinear optical properties and is a new type of infrared nonlinear optical material. The present application can greatly improve the disadvantage of the narrow band gap of phosphorus compounds by introducing halogens into phosphorus compounds. The band gap of CsCd4PI6 reaches 3.0eV, which is the maximum value among the cadmium phosphorus compounds reported so far. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the structure of the inorganic compound crystal CsCd4PI6.

[0034] Figure 2 Schematic diagram of the structure of the inorganic compound crystal CsCd4AsI6.

[0035] Figure 3 Schematic diagram of the structure of the inorganic compound crystal RbCd4PI6.

[0036] Figure 4 In order to analyze the crystal structure based on the X-ray diffraction of CsCd4PI6 single crystal, the fitted X-ray diffraction pattern (simulated value) is compared with the pattern (experimental value) obtained by X-ray diffraction test after the sample CsCd4PI6 is ground into powder.

[0037] Figure 5 In order to analyze the crystal structure based on the X-ray diffraction of CsCd4AsI6 single crystal, the fitted X-ray diffraction pattern (simulated value) is compared with the pattern (experimental value) obtained by X-ray diffraction test after the sample CsCd4AsI6 is ground into powder.

[0038] Figure 6 In order to analyze the crystal structure based on the X-ray diffraction of single crystal RbCd4PI6, the fitted X-ray diffraction pattern (simulated value) is compared with the pattern (experimental value) obtained by X-ray diffraction test after the sample RbCd4PI6 is ground into powder.

[0039] Figure 7 The frequency doubling test results of samples CsCd4PI6, CsCd4AsI6 and RbCd4PI6 and commercial AgGaS2.

[0040] Figure 8 This is the infrared spectrum test result of CsCd4PI6 powder sample.

[0041] Fig. 9This is the infrared spectrum test result of CsCd4AsI6 powder sample.

[0042] Fig.10 This is the infrared spectrum test result of RbCd4PI6 powder sample.

[0043] Fig.11 This is the diffuse reflectance spectrum test result of CsCd4PI6 powder sample.

[0044] Fig.12 This is the diffuse reflectance spectrum test result of CsCd4AsI6 powder sample.

[0045] Fig.13 This is the diffuse reflectance spectrum test result of RbCd4PI6 powder sample. DETAILED DESCRIPTION

[0046] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0047] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0048] Unless otherwise specified, conventional methods were used for testing and instrument settings were those recommended by the manufacturer.

[0049] The tests in this application use the following equipment and methods:

[0050] Single crystal X-ray diffraction: equipped with monochromatic Mo-Kα radiation Single crystal X-ray diffraction (SC-XRD) data were collected on a Rigaku FR-X microfocus diffractometer at 293 K. Integration and reduction of the data set were performed using CrysAlisPro software. Intensity data sets were collected using the ω-scan technique and reduced using the Siemens SHELXTL crystallography software package, and the correctness of the structure was checked using the PLATON program.

[0051] Powder X-ray diffraction: The analysis was performed on a Rigaku MiniFlex 600 diffractometer using Cu-Kα radiation in reflection mode. Powder X-ray diffraction (PXRD) was measured in the range of 5 to 65°, with a step size of 0.02° and a scanning speed of 0.125°min -1 . The test temperature is 293K.

[0052] Frequency doubling and laser damage threshold tests: AM4PnX6 and AGS crystals were sieved into several different particle size ranges (30-50, 50-75, 75-100, 100-150 and 150-200 μm) and then pressed into a container with a thickness of 1 mm and a diameter of 8 mm. Then, their NLO effects were measured under incident laser radiation of 1064, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1910 and 2000 nm using a modified Kurtz-Perry NLO system. Phase matching is satisfied when the nonlinear intensity is positively correlated with the particle size. The laser damage threshold of AM4PnX6 and AGS crystal surfaces with the same size (~3 mm) was measured by using a 1.06 μm laser beam (pulse width of 10 ns and frequency of 1 Hz) as the damage source.

[0053] Infrared transmission test: The infrared transmission spectrum of the wafer was recorded on a Nicolet Magna 750 FT-IR spectrometer in the range of 4000-400 cm -1 The polycrystalline powder of AM4PnX6 was placed directly on the test platform to obtain the vibration peaks of the infrared spectrum.

[0054] Bandgap test: Optical diffuse reflectance spectroscopy was performed at room temperature with a PerkinElmer Lamda-950 UV / Vis / NIR spectrophotometer in the wavelength range of 200-2000nm. BaSO4 plates were used as 100% reflectance comparison standards. The reflectance values ​​were converted to absorbance using the Kubelka-Munk function, and the bandgap was estimated based on the absorption spectrum.

[0055] According to one embodiment of the present application, a novel infrared nonlinear optical material is a material containing d 10 The transition metal phosphorus mixed anion compound crystal has the chemical formula AM4PnX6, wherein A is selected from one of Cs, Rb, K, Na, and Li, M is selected from one of Hg, Cd, and Zn, Pn is selected from one of P, As, and Sb, and X is selected from one of the halogens. 10 The transition metal phosphorus mixed anion compound crystal is a non-centrosymmetric structure, the space group is Pm, belongs to the monoclinic system, and its unit cell parameters are: α=90°, β=90°, γ=90-91°, Z=1.

[0056] According to one embodiment of the present application, 10 The preparation method of the transition metal phosphorus mixed anion compound crystal comprises the following steps:

[0057] Cadmium, mercury, zinc, phosphorus group elements, d10 Transition metal phosphides, d 10 The raw materials of transition metal halide and alkali metal halide are mixed evenly and placed in a quartz tube and evacuated to 10 -1 -10 -2 The Pa tube is sealed, placed in a muffle furnace and heated to 300-900°C at a rate of 30-50°C / h, kept at this temperature for 24-72h, cooled to 300°C at a rate of 1-10°C / h, and then the muffle furnace is turned off and naturally cooled to room temperature to obtain a compound with a chemical formula of AM4PnX6. The raw material of M can be M single substance or M3Pn2 compound or MX2 compound.

[0058] Example 1

[0059] Weigh 300 mg of CsI, Cd, P, and CdI2 in a molar ratio of 1:3:2:1, mix them evenly, and place them in a quartz tube and evacuate to 10 -2 The Pa sealed tube was placed in a muffle furnace, heated to 750°C within 20 hours, kept at this temperature for 60 hours, cooled to 300°C at 3°C / h, and then the muffle furnace was turned off and naturally cooled to room temperature to obtain a crystal with the chemical formula CsCd4PI6. The crystal is colorless and transparent.

[0060] Example 2

[0061] Weigh 300 mg of CsI, Cd, As, and CdI2 in a molar ratio of 1:1:1:2, mix them evenly, and place them in a quartz tube and evacuate to 10 -2 The tube was sealed with Pa and placed in a muffle furnace. It was heated to 750°C within 20 hours. After keeping the temperature for 60 hours, the temperature was lowered to 300°C at 3°C / h. The muffle furnace was turned off and naturally cooled to room temperature to obtain a crystal with the chemical formula of CsCd4AsI6. The color of the crystal is yellow.

[0062] Example 3

[0063] Weigh 300 mg of RbI, Cd, P, and CdI2 in a molar ratio of 1:1:2:2, mix them evenly, and place them in a quartz tube and evacuate to 10 -2 The Pa sealed tube was placed in a muffle furnace, heated to 750°C within 20 hours, kept at this temperature for 60 hours, cooled to 300°C at 3°C / h, and then the muffle furnace was turned off and naturally cooled to room temperature to obtain a crystal with the chemical formula of RbCd4PI6. The crystal color is yellow.

[0064] Example 4

[0065] Weigh 300 mg of CsI, Zn, P, and ZnI2 in a molar ratio of 2:1:2:1, mix them evenly, and place them in a quartz tube and evacuate to 10 -2The Pa sealed tube was placed in a muffle furnace, heated to 750°C within 20 hours, kept at this temperature for 60 hours, cooled to 300°C at 3°C / h, and then the muffle furnace was turned off and naturally cooled to room temperature to obtain a crystal with the chemical formula CsZn4PI6. The crystal is colorless and transparent.

[0066] Example 5

[0067] Weigh 300 mg of CsBr, Cd, P, and CdBr2 in a molar ratio of 1:1:2:3, mix them evenly, and place them in a quartz tube and evacuate to 10 -2 The Pa sealed tube was placed in a muffle furnace, heated to 750°C within 20 hours, kept at this temperature for 60 hours, cooled to 300°C at 3°C / h, and then the muffle furnace was turned off and naturally cooled to room temperature to obtain a crystal with the chemical formula of CsCd4PBr6. The crystal is colorless and transparent.

[0068] Example 6

[0069] Weigh 300 mg of CsI, P, and HgI2 in a molar ratio of 1:2:4, mix them evenly, put them into a quartz tube and evacuate to 10 -2 The tube was sealed with Pa and placed in a muffle furnace, heated to 500°C within 20 hours, kept at this temperature for 60 hours, cooled to 200°C at 3°C / h, and then the muffle furnace was turned off and naturally cooled to room temperature to obtain a crystal with the chemical formula of CsHg4PI6. The color of the crystal is yellow-green.

[0070] Example 7

[0071] Weigh 300 mg of KI, Cd3As2, and CdI2 in a molar ratio of 2:1:3, mix them evenly, and place them in a quartz tube and evacuate to 10 -2 The Pa sealed tube was placed in a muffle furnace, heated to 750°C within 20 hours, kept at this temperature for 60 hours, cooled to 300°C at 3°C / h, and then the muffle furnace was turned off and naturally cooled to room temperature to obtain a crystal with a chemical formula of KCd4AsI6. The crystal color is yellow.

[0072] Test Example 1

[0073] The crystals prepared in Examples 1 to 7 were subjected to single crystal X-ray diffraction and powder X-ray diffraction tests, and the results were as follows:

[0074] The crystal of CsCd4PI6 has a space group of Pm and belongs to the monoclinic system. Its unit cell parameters are: α=90°, β=90.019°, γ=90°, Z=1.

[0075] The crystal of CsCd4AsI6 has a space group of Pm and belongs to the monoclinic system. Its unit cell parameters are: α=90°, β=90.013°, γ=90°, Z=1.

[0076] The crystal of RbCd4PI6 has a space group of Pm and belongs to the monoclinic system. Its unit cell parameters are: α=90°, β=90.201°, γ=90°, Z=1.

[0077] The crystal of CsZn4PI6 has a space group of Pm and belongs to the monoclinic system. Its unit cell parameters are: α=90°, β=90.012°, γ=90°, Z=1.

[0078] The crystal of CsCd4PBr6 has a space group of Pm and belongs to the monoclinic system. Its unit cell parameters are: α=90°, β=90.104°, γ=90°, Z=1.

[0079] The crystal of CsHg4PI6 has a space group of Pm and belongs to the monoclinic system. Its unit cell parameters are: α=90°, β=90.026°, γ=90°, Z=1.

[0080] The crystal of KCd4AsI6 has a space group of Pm and belongs to the monoclinic system. Its unit cell parameters are: α=90°, β=90.208°, γ=90°, Z=1.

[0081] The structures of CsCd4PI6, CsCd4AsI6 and RbCd4PI6 are shown in Figures 1 to 3 As shown in the figure, the X-ray diffraction pattern obtained by fitting according to the crystal structure analyzed by single crystal X-ray diffraction (simulated value) is compared with the X-ray diffraction test pattern (experimental value) of samples CsCd4PI6, CsCd4AsI6 and RbCd4PI6 after grinding into powder. Figure 4-6 As shown, the peak positions and peak intensities in the figure are consistent, indicating that the obtained sample has high purity.

[0082] The crystalline compounds prepared in Examples 1 to 7 are host-guest compounds with a non-centrosymmetric structure. The crystal with the chemical formula CsCd4PI6 prepared in Example 1 is used as a typical example. For the main part, it can be regarded as a Cd atom as the center. Each Cd atom is coordinated with 3 I atoms and 1 P atom to form a [CdPI3] tetrahedral unit. Every 3 [CdPI3] are connected at the top by P atoms to form a planar triangular trimer, and 1 [CdPI3] is connected at the top of these trimers by sharing an I atom. These 4 [CdPI3] tetrahedra together form a T2 supertetrahedron. These T2 supertetrahedrons are connected end to end to form a hole-shaped 3D Cd-P / I main framework in three-dimensional space. It can be clearly seen from the a-axis direction that the planar figure of each main hole is approximately an equilateral triangle, each composed of 6 [CdPI3] tetrahedrons, Cs + As a guest part, it fills in this three-dimensional hole structure.

[0083] Test Example 2

[0084] Taking the crystal powders prepared in Examples 1 to 3 as typical examples, the crystal powders prepared in Examples 1 to 3 and the AGS polycrystalline powder were subjected to frequency doubling test, infrared spectrum test, band gap test, and laser damage threshold test, and the results are as follows:

[0085] Figure 7 The results of the frequency doubling test of samples CsCd4PI6, CsCd4AsI6 and RbCd4PI6 show that under 1064nm laser irradiation, when the particle size is 150-200μm, the frequency doubling coefficient of the powder is 29.6-52.3 times that of AGS, and all are phase matched.

[0086] Figure 8-10 The infrared spectrum test results of CsCd4PI6, CsCd4AsI6 and RbCd4PI6 powder samples show that the infrared transmission range of the series of compounds is 0.5-25.0μm.

[0087] Figure 11-13 The diffuse reflectance spectra test results of CsCd4PI6, CsCd4AsI6 and RbCd4PI6 powder samples show that the band gaps of compounds CsCd4PI6, CsCd4AsI6 and RbCd4PI6 are 3.00eV, 2.69eV and 2.76eV respectively.

[0088] The comparison of the laser damage threshold of samples AM4PnX6 and AGS polycrystalline powder is shown in Table 1. It can be seen that the laser damage threshold of AM4PnX6 is 8.6-15.3 times that of AgGaS2.

[0089] Table 1

[0090]

[0091] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A kind of d 10 A transition metal phosphorus mixed anion compound crystal, characterized in that: The containing 10 The unique crystal formula of transition metal phosphorus mixed anion compound is AM4PnX6; Wherein, A is selected from one of Cs, Rb, K, Na, and Li; M is selected from one of the elements Hg, Cd and Zn; Pn is selected from one of P, As and Sb; X is selected from one of Cl, Br and I.

2. The d-containing compound according to claim 1 10 A transition metal phosphorus mixed anion compound crystal, characterized in that: The containing 10 The crystals of transition metal phosphorus mixed anion compounds belong to the monoclinic system and the space group is Pm.

3. The d-containing compound according to claim 1 10 A transition metal phosphorus mixed anion compound crystal, characterized in that: The containing 10 The unit cell parameters of transition metal phosphorus mixed anion compound crystals are: α=90°, β=90°, γ=90-91°, Z=1.

4. The d-containing compound according to claim 1 10 A transition metal phosphorus mixed anion compound crystal, characterized in that: The containing 10 Transition metal phosphorus mixed anion compound crystals are host-guest compounds with non-centrosymmetric structures. The main part of the host-guest is centered on the M atom, each M atom is coordinated with 3 X atoms and 1 Pn atom to form a [MPnX3] tetrahedral unit, every 3 [MPnX3] are connected at the top by Pn atoms to form a planar triangular trimer, the top of the trimer is connected to 1 [MPnX3] by sharing X atoms, the above 4 [MPnX3] tetrahedrons together form a T2 supertetrahedron, several of the T2 supertetrahedrons are connected end to end to form a three-dimensional channel-shaped 3D Cd-P / I main framework, the shape of the channel cross-section is approximately an equilateral triangle and is composed of 6 [MPnX3] tetrahedrons; A + As a guest part, it is filled in the three-dimensional pore structure.

5. The d-containing compound according to claim 1 10 A transition metal phosphorus mixed anion compound crystal, characterized in that: The containing 10 The transition metal phosphorus mixed anion compound crystal has at least one of the following properties: (1) The frequency multiplication factor is 29.6-52.3 times that of AGS, and both are phase matched; (2) The laser damage threshold is 8.6-15.3 times that of AgGaS2; (3) Band gap value is 2.4-3.3eV; (4) The infrared transmittance range of the powder is 0.4-25.0 μm.

6. The compound containing d according to any one of claims 1 to 5 10 A method for preparing transition metal phosphorus mixed anion compound crystals, characterized in that: The steps include: A mixture including an A source, an M source, a Pn source, and an X source is placed under vacuum conditions, heated for reaction, and cooled to obtain the d-containing 10 Crystals of transition metal phosphorus mixed anion compounds.

7. The preparation method according to claim 6, characterized in that: In the mixture, the element molar ratio of A, M, Pn, and X is (1-4): (1-4): (1-2): (2-9); Preferably, the A source is selected from AX; The M source is selected from at least one of M element, M3Pn2, and MX2; The Pn source is selected from at least one of Pn element and M3Pn2; The X source is selected from at least one of MX2 and AX.

8. The preparation method according to claim 6, characterized in that: The conditions of the heating reaction include: heating to 300-900°C at a rate of 30-50°C / h, and then keeping the temperature for 24-72h; Preferably, the vacuum condition includes a vacuum degree of 10 -1 -10 -2 Pa.

9. The preparation method according to claim 6, characterized in that: The cooling conditions include: cooling to 300° C. at a rate of 1-10° C. / h and then naturally cooling to room temperature.

10. The compound containing d according to any one of claims 1 to 5. 10 The transition metal phosphorus mixed anion compound crystal or the d-containing compound obtained by the preparation method according to any one of claims 6 to 9 10 The application of transition metal phosphorus mixed anion compound crystals as infrared nonlinear optical materials in the optical field.

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