A copper (I) complex scintillator material with thermally stable radioluminescence performance, and a preparation method and application thereof

Abstract

This invention discloses a thermally stable copper(I) complex scintillator material, its preparation method, and its applications, belonging to the field of scintillator luminescent materials. The material has the general formula [Cu(N^N)(P^P)]X, where N^N is a sterically hindered substituent and P^P is a rigid bisphosphine chelate ligand. This type of material uses readily available and inexpensive copper as the metal center, and through ligand design, achieves simultaneous optimization within a semi-cage-like chelate structure, significantly enhancing scintillation performance and greatly improving luminescence stability at high temperatures. Compared with unmodified copper(I) complexes, the light yield is increased by ≥90%; the radiative luminescence intensity retention rate at 110℃ is ≥70%, significantly superior to commercial BGO scintillators. It is suitable for X-ray detection and imaging, especially exhibiting superior applicability in continuous operation and extreme high-temperature environments, effectively solving the problem of poor thermal stability commonly found in existing commercial scintillators.

Description

Technical Field

[0001] This invention relates to a copper(I) complex scintillator material with thermally stable radiative luminescence properties, its preparation method, and its applications. This type of material belongs to the field of scintillator luminescent materials and can be widely used in medical CT, security inspection, high-energy physics, nuclear medicine, and industrial non-destructive testing. Background Technology

[0002] Scintillator materials can convert high-energy radiation such as X-rays and gamma rays into visible-ultraviolet light for non-destructive and sensitive radiation detection and imaging, and are widely used in medical imaging, security inspection, industrial inspection, space exploration and other fields. Traditional inorganic scintillators (such as NaI(Tl), CsI(Tl), BGO, etc.) have excellent performance, but they have shortcomings such as high crystal growth temperature, difficulty in fabricating large-area flexible devices, moisture absorption, slow decay, limited light yield, and high cost.

[0003] In recent years, organic scintillators have attracted attention due to their low cost, high stability, ease of processing, and flexibility. However, their low atomic number leads to weak X-ray absorption, and approximately 75% of excited-state excitons cannot emit light, limiting light yield. Metal-organic complex scintillators can efficiently collect and convert triplet excitons under X-ray excitation, enabling the utilization of previously non-luminescent triplet excitons and "activating" them to increase light yield. However, these rare-earth or noble metal triplet excitons currently face limitations such as high cost and limited reserves. Furthermore, these scintillators all face severe practical challenges: severe thermal quenching at high temperatures. Increased temperature accelerates non-radiative decay channels, leading to a sharp drop in luminous efficiency and unstable scintillation output, significantly limiting their operating temperature range and making them difficult to deploy in thermally demanding environments. Summary of the Invention

[0004] To develop thermally stable metal-organic complex scintillators based on inexpensive metals and simplify material preparation processes, this invention employs a semi-cage-like four-coordinate copper (I) complex and, through ligand engineering, develops a class of high-temperature adaptive scintillators based on thermally activated delayed fluorescence (TADF) copper (I) complexes. The scintillator material maintains continuous and stable luminescence performance across a wide temperature range, making it suitable for radiation detection devices operating under broad temperature conditions.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a copper(I) complex scintillator material with thermally stable radiative luminescence properties. The scintillator material is a chelated copper(I) complex with a semi-cage-like rigid framework, formed by the chelation of a copper(I) metal center with N^N ligands and P^P ligands, and its general formula is [Cu(N^N)(P^P)]X, wherein: Cu is a +1 copper ion, serving as a metallic center; N^N is a bidentate nitrogen-containing ligand; P^P is a bidentate phosphorus-containing ligand; X represents the counteracting anion; The scintillator material maintains significant radiative emission in the temperature range of 25-110 °C, and the intensity retention rate of X-ray excitation at high temperature (110 °C) is ≥ 70%, and the light yield is ≥ 90% higher than that of Cu(I) complex without ligand engineering modification.

[0006] Preferably, the N^N is a bidentate nitrogen-containing ligand selected from substituted derivatives of 1,10-phenanthroline, 2,2′-bipyridine, or 2-(1H-pyrazol-1-yl)pyridine. The substituted derivative has at least one substituent on the aromatic or heteroaromatic ring of the ligand. The substituent contains a halogen atom with an atomic number ≥17 to produce a heavy atom effect, increase the X-ray absorption cross section, and the position of the substituent enables it to produce a steric hindrance effect on the copper (I) center, suppressing molecular thermal vibrations.

[0007] Preferably, the substituted derivative of the N^N ligand has two substituents on the aromatic or heteroaromatic ring of the ligand, the two substituents being located at positions that can produce a steric hindrance effect on the copper (I) center, each substituent being independently selected from methyl, chlorine or bromine, and at least one of the substituents being a halogen atom with an atomic number ≥17.

[0008] Preferably, the N^N ligand is 2,9-dimethyl-1,10-phenanthroline, 2,9-dichloro-1,10-phenanthroline, 2,9-dibromo-1,10-phenanthroline, 4,6′-dichloro-2,2′-bipyridine, or 2-bromo-6-(1H-pyrazol-1-yl)pyridine.

[0009] Preferably, the P^P is a bidentate phosphorus-containing ligand selected from bis(2-diphenylphosphine) ether or 9,9-dimethyl-4,5-bis(diphenylphosphine)oxanthracene, and its derivatives in which the 3,3′- or 5,5′-positions of the benzene ring are mono- or di-substituted with chlorine, bromine or tert-butyl.

[0010] Preferably, the counter anion X is hexafluorophosphate.

[0011] In a second aspect, the present invention provides a method for preparing the copper(I) complex scintillator material, comprising the following steps: Step (1): Dissolve the bisphosphine ligand P^P and the copper (I) source in an organic solvent at a molar ratio of 1:1, and stir the reaction at room temperature to coordinate the bisphosphine ligand with the copper (I) ions; Step (2): Add the substituted derivative of N^N ligand to the reaction solution obtained in step (1), wherein the molar ratio of the substituted derivative of N^N ligand to the copper (I) source is 1:1, and continue to stir the reaction at room temperature; Step (3): After the reaction is complete, the solvent is removed, and the crude product is purified by washing and vapor diffusion crystallization to obtain the copper (I) complex scintillator material.

[0012] Preferably, the copper (I) source in step (1) is copper tetra(acetonitrile)hexafluorophosphate (I) or copper tetra(acetonitrile)tetrafluoroborate (I), and the organic solvent is dichloromethane.

[0013] Preferably, the washing in step (3) is carried out using cold diethyl ether, and the vapor diffusion crystallization is carried out using a dichloromethane / diethyl ether system.

[0014] Thirdly, the present invention provides an application of the copper (I) complex scintillator material described above in the preparation of X-ray imaging, CT imaging or high-energy ray detection devices.

[0015] The present invention has the following beneficial effects: (1) For the first time, the TADF mechanism and ligand engineering strategy were synergistically applied to the thermal stability design of scintillators, breaking through the bottleneck of traditional thermal quenching. Existing commercial inorganic scintillators (such as BGO) and metal halide scintillators both face severe high-temperature thermal quenching problems: heating accelerates nonradiative relaxation channels, leading to a sharp decline in scintillation output efficiency. BGO's radiative emission intensity at 110℃ only maintains 30–40% of its room-temperature value, severely limiting its practical deployment in continuous operation and thermally harsh environments. This invention creatively combines the thermally activated delayed fluorescence (TADF) mechanism with a sterically hindered framework rigidity strategy. Under high-temperature conditions, it continuously utilizes triplet excitons through an efficient reverse intersystem crossing (RISC) process, while simultaneously suppressing molecular thermal vibrations and nonradiative losses using sterically hindered N^N ligand derivatives, achieving thermally stable luminescence through a dual-mechanism synergy. The copper(I) complex scintillator material described in this invention maintains continuous and stable radiative emission performance over a wide temperature range of 25–110℃, with an X-ray excited radiative emission intensity retention rate of ≥70% at 110℃. The optimal sample still maintains a luminescence efficiency of over 85% at 100℃, far superior to BGO at the same temperature. Meanwhile, the unmodified ligand-engineered reference compound [Cu(POP)(phen)][PF6] exhibited severe thermal quenching under the same heating conditions, with its radiative emission signal almost disappearing at high temperatures, failing to meet practical application requirements.

[0016] (2) Achieving a significant increase in light production through ligand engineering This invention introduces heavy atom halogen substituents (Cl, Br) at the 2,9-positions of the N^N ligand (1,10-phenanthroline), thereby accelerating spin-orbit coupling through the heavy atom effect, promoting the reverse population of triplet excitons to singlet states, and improving radiative transition efficiency. At the same time, the large atomic numbers of Cl and Br (17 and 35, respectively) significantly increase the absorption cross-section of the organic ligand for X-rays, thereby improving the material's high-energy ray capture efficiency.

[0017] (3) The semi-cage-like rigid chelate framework effectively suppresses excited-state Jahn-Teller distortion, improving quantum efficiency and thermal stability from the structural source. The rigid chelating framework of the P^P bidentate phosphorus-containing ligand (POP or Xantphos) locks the copper(I) center within a distorted tetrahedral geometry, significantly suppressing the Jahn-Teller distortion (i.e., relaxation of the excited state towards a planar quadrilateral configuration) characteristic of copper(I) complexes. This distortion is one of the main reasons for the low luminescence quantum yield of copper(I) complexes. The semi-cage-like rigid framework constructed by the P^P ligand and the sterically hindered N^N ligand effectively maintains the rigid geometry of the complex over a wide temperature range from room temperature to high temperatures, thus maintaining high radiative luminescence efficiency throughout the entire operating temperature range.

[0018] (4) With copper as its metal center, which is cheap, low in toxicity and abundant, it has significant resource economic advantages. Existing high-performance metal-organic complex scintillators mainly rely on rare and precious metals such as iridium (Ir), platinum (Pt), and europium (Eu), which are costly and have limited global reserves, making it difficult to support large-scale industrial applications. This invention uses copper (I) as the metal center. Copper resources are abundant and inexpensive (approximately one ten-thousandth the price of iridium), and its toxicity is significantly lower than that of heavy metals. While achieving high light yield and thermally stable scintillation performance, it significantly reduces material costs, making it feasible for large-scale industrial production.

[0019] (5) All preparation steps can be completed at room temperature, the process is simple and suitable for mass production. The synthesis of the complexes described in this invention does not require high-temperature calcination, complex vapor deposition, or sophisticated inert atmosphere reactors. All preparation steps are completed at room temperature in a common organic solvent (dichloromethane), with a reaction time of only about 1.5 hours. The post-processing is simple (cold ether washing / vapor diffusion crystallization). These process characteristics endow the materials of this invention with excellent processability and batch consistency, unlike traditional inorganic scintillators which are heavily dependent on high-temperature crystal growth equipment.

[0020] (6) The material has both solution processability and mechanical flexibility, and can be used to prepare flexible scintillation films, thus expanding its application scenarios. The copper(I) complex described in this invention exhibits excellent solubility in common organic solvents (such as dichloromethane), allowing for the preparation of flexible composite scintillation films (doping concentration 30 wt%) by solution blending with flexible polymer matrices such as polystyrene (PS). This eliminates the need for sintering or hot pressing, and the entire film preparation process is conducted at room temperature. Experimental verification of the resulting flexible scintillation screen successfully achieved clear X-ray imaging of the kernel and encapsulated metal spring microstructure within plant seeds, maintaining good imaging clarity across a temperature range of 25–110°C. In contrast, under the same conditions, the BGO scintillation screen exhibited significantly darkened images and lost structural details at 368 K (approximately 95°C). These characteristics make the material of this invention particularly suitable for applications requiring radiation imaging under complex surfaces and high-temperature conditions, such as medical CT, industrial non-destructive testing, and security inspections. Attached Figure Description

[0021] Figure 1 It is a single-crystal structure of the [Cu(POP)(phen)][PF6] complex scintillator.

[0022] Figure 2 The photoluminescence and radiative luminescence properties of the [Cu(POP)(phen)][PF6] scintillator.

[0023] Figure 3 It is a single-crystal structure of a scintillator after ligand modification.

[0024] Figure 4 The photoluminescence and radiative emission properties of the scintillator before and after ligand modification are shown.

[0025] Figure 5 This is a comparison chart showing the increase in scintillator light yield after ligand modification.

[0026] Figure 6 The photoluminescence and radiative emission properties of the Xantphos phosphine ligand system scintillator after ligand modification are shown.

[0027] Figure 7 This is a comparison of the scintillator light yield of the Xantphos phosphine ligand system before and after ligand modification.

[0028] Figure 8 This is a graph showing the change in relative radiative luminescence intensity of the scintillator after ligand modification during the heating process.

[0029] Figure 9 This is an X-ray imaging effect of a scintillator thin film.

[0030] Figure 10 X-ray imaging effect of thermally stable scintillator thin film during heating process. Detailed Implementation

[0031] Comparative Example 1 [Cu(POP)(phen)][PF6] scintillator material Preparation method: POP (116 mg, 0.21 mmol, 1.1 eq) and copper(I) tetra(acetonitrile)hexafluorophosphate (74.5 mg, 0.20 mmol, 1.0 eq) were added to a 50 mL single-necked flask, followed by the addition of 20 mL of anhydrous dichloromethane. The mixture was stirred at room temperature for 30 minutes. Then, 1,10-phenanthroline (36.4 mg, 0.20 mmol, 1.0 eq) was added, and stirring continued for 1 hour. The reaction mixture was concentrated to dryness by rotary evaporation. The resulting oily residue was washed with cold diethyl ether (3 × 5 mL) to remove free ligands and byproducts. The crude product was dissolved in a small amount of dichloromethane and then slowly diffused and crystallized in an ether atmosphere. A yellow solid precipitated, which was filtered, washed with diethyl ether, and dried under vacuum to obtain the target complex crystals.

[0032] Characterization of [Cu(POP)(phen)][PF6] single crystals: The single crystal structure of the copper complex was determined using a single crystal diffractometer. Figure 1 As shown. Under X-ray excitation, the complex exhibits scintillation properties of radioactive luminescence, as shown in the results. Figure 2 .

[0033] The rigid chelate framework of the semi-cage structure formed by the interaction of 1,10-phenanthroline and POP ligand provides significant steric hindrance, thereby stabilizing the geometry of the complex and reducing non-radiative transitions under high-energy radiation excitation, thus giving it scintillation properties. Green luminescence can be clearly observed under X-ray excitation.

[0034] Example 1

[0035] The ligand derivatives such as Me-phen, Cl-phen, and Br-phen are all commercially available products and can be purchased directly without the need for self-synthesis.

[0036] The difference from Comparative Example 1 is that the N^N ligands in Comparative Example 1 are replaced with equimolar amounts of Me-phen, Cl-phen and Br-phen ligands, and the rest of the operations are the same as in Comparative Example 1.

[0037] Specific preparation method: POP (116 mg, 0.21 mmol, 1.1 eq) and copper(I) tetra(acetonitrile) hexafluorophosphate (74.5 mg, 0.20 mmol, 1.0 eq) were added to a 50 mL single-necked flask, followed by the addition of 20 mL of anhydrous dichloromethane. The mixture was stirred at room temperature for 30 minutes. Subsequently, Me-phen, Cl-phen, and Br-phen (0.20 mmol, 1.0 eq) were added, and stirring was continued for 1 hour. The reaction solution was concentrated to dryness by rotary evaporation. The resulting oily residue was washed with cold diethyl ether (3 × 5 mL) to remove free ligands and byproducts. The crude product was dissolved in a small amount of dichloromethane and then slowly diffused and crystallized in an ether atmosphere. A yellow solid precipitated, which was filtered, washed with diethyl ether, and dried under vacuum to obtain the target complex crystals.

[0038] The crystal structures of these complexes [Cu(POP)(Me-phen)][PF6], [Cu(POP)(Cl-phen)][PF6], and [Cu(POP)(Br-phen)][PF6] are as follows: Figure 3 As shown, its luminescence performance results are as follows: Figure 4 As shown, the radiative luminescence properties of the modified complex are as follows: Figure 5 As shown, both light production and output have been greatly improved.

[0039] These high-temperature adaptive scintillator materials, based on copper(I) complex scintillators with thermally activated delayed fluorescence properties, achieve thermally stable "thermal exciton" trapping through a dual mechanism of efficient reverse intersystem crossing (RISC) and steric hindrance-suppressed nonradiative transitions. Furthermore, the 2,9-position disubstituted o-phenanthroline forms a semi-cage configuration, increasing steric hindrance and enhancing framework rigidity, further suppressing high-temperature thermal vibrations and nonradiative losses; the introduction of halogen heavy atoms simultaneously increases the X-ray absorption cross-section, thereby synergistically enhancing radiative emission performance.

[0040] Example 2 Xantphos ligand-modified scintillator materials Preparation method: Replace the POP ligand in Example 1 with Xantphos ligand in equimolar form, and perform the other operations as in Example 1.

[0041] These complexes, [Cu(Xantphos)(Me-phen)][PF6], [Cu(Xantphos)(Cl-phen)][PF6], and [Cu(Xantphos)(Br-phen)][PF6], exhibit the same ligand engineering strategy as described in Example 1, and their luminescence performance results are as follows: Figure 6 As shown, the radiative luminescence properties of the modified complex are as follows: Figure 7As shown, the light yield exhibits the same variation pattern as the complex in Example 1, both showing a significant increase. Within the scope of the technical concept of this invention, various simple modifications can be made to the technical solution of this invention, including combining the various ligand features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this invention and fall within the protection scope of this invention.

[0042] Example 3 Thermally Stable Scintillator Materials and Their X-ray Imaging Scintillator film preparation method: After grinding the copper (I) complex, it was incorporated into a dichloromethane solution of PS at a concentration of 30 wt% relative to polystyrene (PS); ultrasonically dispersed for 10 min, poured into a mold, and air-dried at room temperature to obtain a flexible film.

[0043] The copper complex scintillators [Cu(POP)(Me-phen)][PF6], [Cu(POP)(Cl-phen)][PF6], and [Cu(POP)(Br-phen)][PF6] modified with ligand engineering were tested using a variable-temperature apparatus. Compared with conventional commercial and most existing scintillators (such as BGO, which exhibits only 30-40% radiative luminescence at 110°C, while this material maintains over 70% at that temperature), they show significant advantages: Figure 8 The results showed that the X-ray excited radiative luminescence intensity remained relatively stable during the heating process, with the optimal luminescence efficiency maintaining 85% even at 100°C, confirming that this complex scintillator can achieve stable X-ray imaging over a wide temperature range. Further temperature-dependent radiative luminescence testing was conducted on [Cu(POP)(phen)][PF6]. The luminescence was too low at high temperatures to be detected.

[0044] Taking [Cu(POP)(Br-phen)][PF6] as an example, the resulting scintillator film exhibits good imaging resolution, such as... Figure 9 As shown, a plant seed and a packaged metal spring are placed sequentially between a scintillator screen and an X-ray source. Under X-ray irradiation, the metal spring hidden inside the opaque capsule and the kernel inside the plant seed can be clearly distinguished on the scintillator screen using a commercial digital camera. Furthermore, due to ligand engineering modifications, its steric hindrance is increased and its framework rigidity is further enhanced, suppressing high-temperature thermal vibration and non-radiative losses. This achieves imaging thermal stability not found in commercial scintillators, maintaining good imaging performance between 25-110℃. Figure 10The results of X-ray imaging of encapsulated metal bolts using BGO and the scintillator material prepared according to this invention under different temperature conditions are shown. The encapsulated metal bolts were placed between a scintillator screen and an X-ray source, and imaging data were recorded using a commercial digital camera at different temperatures. At room temperature, both scintillator materials clearly imaged the internal structure of the capsule. However, when heated to 368 K, a stark contrast emerged: the scintillator film prepared according to this invention maintained image clarity, while the BGO-based image became significantly darker and eventually lost all structural details. Because this type of scintillator material maintains continuous and stable luminescence performance across a wide temperature range, it is suitable for radiation detection devices operating under broad temperature conditions.

Claims

1. A copper(I) complex scintillator material with thermally stable radiative luminescence properties, characterized in that, The scintillator material is a chelated copper(I) complex with a semi-cage-like rigid framework, and its general formula is [Cu(N^N)(P^P)]X, wherein: Cu is a +1 copper ion, serving as a metallic center; N^N is a bidentate nitrogen-containing ligand; P^P is a bidentate phosphorus-containing ligand; X represents the counteracting anion; The scintillator material maintains a radiative luminescence intensity retention rate of ≥70% within a temperature range of 25-110 °C.

2. The copper(I) complex scintillator material according to claim 1, characterized in that, The N^N is a bidentate nitrogen-containing ligand selected from substituted derivatives of 1,10-phenanthroline, 2,2′-bipyridine, or 2-(1H-pyrazol-1-yl)pyridine, wherein the substituted derivative has at least one substituent on the aromatic or heteroaromatic ring of the ligand, the substituent containing a halogen atom with an atomic number ≥17, and the position of the substituent enables it to produce a steric hindrance effect on the copper (I) center.

3. The copper(I) complex scintillator material according to claim 1, characterized in that, The substituted derivative of the N^N ligand has two substituents on the aromatic or heteroaromatic ring of the ligand. The two substituents are located at positions that can produce a steric hindrance effect on the copper (I) center. Each substituent is independently selected from methyl, chlorine or bromine, and at least one of the substituents is a halogen atom with an atomic number ≥17.

4. The copper(I) complex scintillator material according to claim 1, characterized in that, The N^N ligand is 2,9-dimethyl-1,10-phenanthroline, 2,9-dichloro-1,10-phenanthroline, 2,9-dibromo-1,10-phenanthroline, 4,6′-dichloro-2,2′-bipyridine, or 2-bromo-6-(1H-pyrazol-1-yl)pyridine.

5. The copper(I) complex scintillator material according to claim 1, characterized in that, The P^P is a bidentate phosphorus-containing ligand selected from bis(2-diphenylphosphine) ether or 9,9-dimethyl-4,5-bis(diphenylphosphine)oxanthracene, and its derivatives whose 3,3′- or 5,5′-positions on the benzene ring are mono- or di-substituted with chlorine, bromine or tert-butyl.

6. The copper(I) complex scintillator material according to claim 1, characterized in that, The counter anion X is hexafluorophosphate.

7. A method for preparing a copper(I) complex scintillator material according to any one of claims 1-6, characterized in that, Includes the following steps: Step (1): Dissolve the bisphosphine ligand P^P and the copper (I) source in an organic solvent at a molar ratio of 1:1, and stir the reaction at room temperature to coordinate the bisphosphine ligand with the copper (I) ions; Step (2): Add the substituted derivative of N^N ligand to the reaction solution obtained in step (1), wherein the molar ratio of the substituted derivative of N^N ligand to the copper (I) source is 1:1, and continue to stir the reaction at room temperature; Step (3): After the reaction is complete, the solvent is removed, and the crude product is purified by washing and vapor diffusion crystallization to obtain the copper (I) complex scintillator material.

8. The method according to claim 7, characterized in that, The copper (I) source in step (1) is copper tetra(acetonitrile)hexafluorophosphate (I) or copper tetra(acetonitrile)tetrafluoroborate (I), and the organic solvent is dichloromethane.

9. The method according to claim 7, characterized in that, The washing in step (3) is carried out using cold diethyl ether, and the vapor diffusion crystallization is carried out using a dichloromethane / diethyl ether system.

10. The use of the copper (I) complex scintillator material according to any one of claims 1-6 in the preparation of X-ray imaging, CT imaging or high-energy ray detection devices.

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