A method for screening fluorescent powder materials with excellent resistance to thermal quenching

Abstract

The present application relates to the field of lighting and the technical field of fluorescent powder material, and in particular to a method for screening fluorescent powder material with excellent anti-thermal quenching performance, comprising the following steps: obtaining the crystal structure of a substrate and determining the lattice site of the crystal structure; using a luminescent center to replace the lattice site to construct a series of fluorescent powder models; using first principle calculation to calculate the lattice thermal conductivity and electronic structure of the series of fluorescent powder models; performing preliminary screening on the series of fluorescent powder models according to the calculated electronic structure to obtain the series of fluorescent powder models with luminescent characteristics; and comparing the lattice thermal conductivities of the series of fluorescent powder models screened preliminarily to screen out the fluorescent powder model with excellent anti-thermal quenching performance. The present application can greatly save time and trial and error cost through the method of theoretical calculation, greatly reduce the development cost of commercial fluorescent powder, and improve the efficiency.

Description

Technical Field

[0001] This invention relates to the fields of lighting and phosphor materials, specifically to a method for screening phosphor materials with excellent resistance to thermal quenching. Background Technology

[0002] Phosphors are an important raw material in the manufacturing process of lighting equipment. Their physicochemical properties and morphological characteristics significantly influence the quality of lighting equipment, especially white LEDs. Among these, the thermal stability of phosphors is a crucial factor affecting their widespread application in lighting, displays, and luminescence temperature measurement. Thermal quenching of phosphors, also known as temperature quenching, refers to the phenomenon where, under short-wavelength excitation, the phosphor gradually heats up during photoluminescence, either externally or internally, resulting in a decrease in luminescence intensity or even complete cessation of luminescence. Therefore, finding phosphors with excellent resistance to thermal quenching is of paramount importance.

[0003] Currently, the Gurney-Mott equation and its derivatives are commonly used to characterize the thermal quenching phenomenon of phosphors, i.e., the rapid decrease in luminescence intensity or luminescence efficiency with increasing temperature.

[0004]

[0005]

[0006] Among them, Γ v Γ0 is the radiative transition probability, Γ0 is the non-radiative transition probability caused by heat, ΔE is the energy barrier for the non-radiative transition, and k is the energy barrier for the non-radiative transition. B Let η be the Boltzmann constant, T be the temperature, A be a certain constant, η be the luminous efficiency, I0 be the luminous intensity at room temperature (25℃), and I(T) be the luminous intensity at temperature T.

[0007] Dorenbos et al. are studying photoluminescence in Eu... 2+ In the thermal quenching mechanism of doped phosphors, it is believed that Eu 2+ The excited-state 5d electrons are thermally ionized into the matrix conduction band, and then nonradiatively recombine elsewhere to return to the ground state. For example... Figure 1 As shown, in Eu 2+ In doped phosphors, the activation energy is the band gap difference between the lowest 5d band and the conduction band bottom. He assumes the probability of thermally induced nonradiative transitions is 3 × 10⁻⁶. 13 Hz (phonon energy is 1000 cm⁻¹) -1 Eu 2+ 4f 6 5d 1 →4f 7 The radiation probability is 1.1 × 10⁻⁶. 6Hz; from this, he summarized the following relationship between thermal activation energy and quenching temperature (the temperature at which the luminescence intensity decreases to half of its low-temperature value):

[0008]

[0009] Currently, the thermal quenching performance of phosphors is mainly determined experimentally; there are no relevant studies or patents, and predictions are only made using theoretical calculations. Taking the red phosphor SrLiAl3N4:Eu as an example... 2+ For example, Alexander Moewes' team used SLAN:Eu phosphor thermal quenching data to obtain the thermal activation energy ΔE = 0.28 eV by fitting formula (2); then they used resonant inelastic X-ray scattering technology to determine the 5d-CB bandgap difference ΔE. eC It is 0.2±0.1eV.

[0010] In their research results, when the temperature reaches 200℃, its luminescence intensity only drops to 95% of that at room temperature, indicating that the quenching temperature is greater than 200℃ and the luminescence thermal stability is excellent. However, the thermal activation energy obtained from the above measurements, and the quenching temperature range obtained using formula (3) are 68~204K, indicating that the thermal quenching of this material is very severe, which is seriously inconsistent with the experimental phenomena. This shows that the thermal activation energy is not sufficient to explain the excellent thermal stability of this phosphor. On the other hand, the quenching temperature T, which was measured experimentally and summarized by Dorenbos, is... 0.5 The thermal activation energy obtained by reverse calculation is not equivalent to the thermal activation energy ΔE obtained by fitting formula (2). Furthermore, Jia Yongchao obtained the SrLiAl3N4:Eu... 2+ The thermal activation energies at the two sites of the phosphor are 2.727 eV and infinity, respectively. This further demonstrates that the thermal quenching activation energy is insufficient to characterize the phosphor SrLiAl3N4:Eu. 2+ Its luminescence and thermal stability properties.

[0011] In view of this, this patent proposes a method based on theoretical calculation to measure the thermal quenching resistance of phosphors. Summary of the Invention

[0012] To address the problem that the thermal activation energy of thermal quenching is insufficient to characterize the luminescence thermal stability of phosphors in existing technologies, the present invention aims to provide a method for screening phosphor materials with excellent resistance to thermal quenching.

[0013] The method of this invention mainly employs a single luminescent central ion to replace specific lattice sites to construct a phosphor model. Then, the lattice thermal conductivity of the phosphor model is calculated using first-principles methods of density functional theory. Finally, by comparison, it is determined whether the phosphor prepared by doping the target crystal possesses excellent thermal quenching performance. This invention, through theoretical calculations, can significantly save time and trial-and-error costs, greatly reducing the development cost of commercial phosphors and improving efficiency.

[0014] To achieve the above objectives, the technical solution of the present invention is as follows.

[0015] One embodiment of the present invention provides a method for screening phosphor materials with excellent resistance to thermal quenching, comprising the following steps:

[0016] The crystal structure of the matrix is ​​obtained, and the lattice sites of the crystal structure are determined; the luminescent centers are used to replace the lattice sites to construct a series of phosphor models;

[0017] The lattice thermal conductivity and electronic structure of the series of phosphor models were calculated using first-principles calculations;

[0018] The series of phosphor models were initially screened based on the calculated electronic structure to obtain a series of phosphor models with luminescent properties.

[0019] The lattice thermal conductivity of the initially screened series of phosphor models was compared to select phosphor models with excellent resistance to thermal quenching.

[0020] In a preferred embodiment, the lattice sites of the crystal structure are lattice sites that can be replaced by luminescent centers.

[0021] In a preferred embodiment, the process of constructing a series of phosphor models further includes:

[0022] The elements of the lattice sites and the luminescent centers are compared and analyzed to ensure that the lattice sites match the luminescent ions.

[0023] In a preferred embodiment, the condition for ensuring that the lattice sites match the luminescent ions is:

[0024] The elements of the lattice sites match the size of the luminescent centers; and

[0025] The elements at the lattice sites are in charge balance with those at the luminescent centers.

[0026] In a preferred embodiment, when the elements of the lattice sites are not in charge with the charge of the luminescent centers, charge compensation is performed to ensure that the constructed series of phosphor models are in charge balance.

[0027] In a preferred embodiment, the method for charge compensation is one of vacancy, interstitial doping, or asymmetric charge substitution;

[0028] The vacancy is achieved by utilizing cation vacancies to balance the charge.

[0029] The interstitial doping utilizes anion interstitial doping to balance the charge.

[0030] The asymmetric charge substitution is achieved by using unequal-valence ions to balance the charge.

[0031] In a preferred embodiment, the vacancy cation used in the vacancy is Li. + ;

[0032] The anion used in the interstitial doping is X. - ;

[0033] The cation used in the asymmetric charge substitution is Mg. 2+ .

[0034] In a preferred embodiment, the matrix is ​​any one of nitrides, halides, oxides, nitrogen oxides, silicates, and phosphates;

[0035] The luminescent center is a rare earth ion or a transition metal ion.

[0036] In a preferred embodiment, the rare earth ion is Ce. 3+ 、Nd 3+ Dy 3+ Eu 2+ Eu 3+ Pr 3+ Any one of them;

[0037] The transition metal ion is Cr. 3+ Mn 2+ Pb 2+ Any one of them.

[0038] In a preferred embodiment, the criteria for selecting a phosphor model with excellent resistance to thermal quenching are:

[0039] Lattice thermal conductivity ≥ 0.6 W / (m·K).

[0040] In a preferred embodiment, it further includes:

[0041] The lattice thermal conductivity of existing phosphors corresponding to the matrix was calculated using first-principles calculations.

[0042] The lattice thermal conductivity of the initially screened series of phosphor models was compared with that of existing phosphors to screen out phosphor models with excellent resistance to thermal quenching.

[0043] In a preferred embodiment, the specific method for calculating the lattice thermal conductivity of the series of phosphor models using first-principles calculations is as follows:

[0044] The series of phosphor models were structurally optimized based on first-principles calculations to obtain an optimized crystal structure.

[0045] The force constants are obtained by moving atoms to calculate the forces acting on the atoms in the optimized crystal structure.

[0046] The force constant is processed to obtain the lattice thermal conductivity of the phosphor model.

[0047] In this invention, the method for obtaining thermal conductivity is calculated using software. The software used includes two types: one is software for calculating the forces acting on structural optimization and atomic movement, including PWSCF, SIESTA, VASP, CASTEP, ABINIT, and WIEN2K; the other uses density functional perturbation theory to calculate the atomic force constants, with a convergence criterion of 10 for the total electron energy. -8 eV; another type is software that processes force constants to obtain phonon band structure, density of states, and lattice thermal conductivity, including phonopy, phono3py, and ShengBTE, which use a smearing method with SIGMA of 0.1 instead of the linear tetrahedral method.

[0048] In some preferred embodiments, the specific method for obtaining the lattice thermal conductivity of the phosphor model is as follows:

[0049] 1) Structural optimization: Theoretical calculations are based on first-principles calculations, and the exchange-correlation functional is performed using the GGA-PBE method. Furthermore, calculations for all systems containing d and f orbital electrons consider LSDA+U. eff The range is 0 to 10 eV, for example, using U eff =2.5eV to handle strongly correlated Eu 4f electrons. During structure optimization, the convergence criteria for total electron energy and atomic forces are set to 10. -5 eV and A step-by-step convergence method can be adopted to reach the convergence criterion, and a quasi-Newton algorithm can be used for self-consistent computation. The minimum distance between the K points sampled in the first Brillouin zone is... The generated grid is centered at the gamma point.

[0050] 2) The force constant is calculated by moving atoms to determine the forces acting on them. The distance the atom is moved when calculating the second-order force constant is... The distance the atom is moved when calculating the third-order force constant is: The convergence criterion is the total electron energy 10. -8 eV.

[0051] 3) Calculate the lattice thermal conductivity using force constant processing software such as phono3py or ShengBTE. The minimum distance between the K points sampled in the first Brillouin zone is... The generated grid is centered at the gamma point.

[0052] The beneficial effects of this invention are:

[0053] 1. The method of the present invention mainly uses a single luminescent central ion to replace a specific lattice site to construct a phosphor model, and then calculates the lattice thermal conductivity of the phosphor model using the first-principles method of density functional theory; then, by comparison, it is determined whether the phosphor prepared by doping the target crystal has excellent thermal quenching performance.

[0054] 2. The present invention can save a lot of time and trial and error costs through theoretical calculation, greatly reduce the development cost of commercial phosphors, and improve efficiency. Attached Figure Description

[0055] Figure 1 It is photoluminescent Eu 2+ Schematic diagram of the thermal quenching principle of phosphor-doped phosphors. In the diagram, Q... g Q is the effective collective configuration coordinate of the ground state at the equilibrium position; e Q is the effective collective configuration coordinate of the excited state at the equilibrium position; C It is the effective collective configuration coordinate when the base potential energy curve and the excited potential energy curve intersect; hv g It is the ground state phonon energy; hv e It is the energy of the excited-state phonon; E ab It absorbs energy, and it also generates energy; E em It is the emitted energy; ΔE eC It is the energy difference between the lowest 5d excited state and the conduction band bottom; ΔE C It is the energy difference between the crossover point and the lowest 5d excited state; ΔE Vg It represents the energy difference between the ground state and the top of the valence band; the solid black circle represents an electron; the hollow black circle represents a hole.

[0056] Figure 2 This is a schematic diagram of the process for screening phosphor materials with excellent resistance to thermal quenching, provided by one embodiment of the present invention.

[0057] Figure 3 This is an embodiment of the SrSiN2:Eu provided by the present invention. 2+ Band structure diagram of phosphor. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0059] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Currently, the Gurney-Mott equation and its derivatives are commonly used to characterize the thermal quenching phenomenon of phosphors, i.e., the rapid decrease in luminescence intensity or luminescence efficiency with increasing temperature.

[0061]

[0062]

[0063] Among them, Γ v Γ0 is the radiative transition probability, Γ0 is the non-radiative transition probability caused by heat, ΔE is the energy barrier for the non-radiative transition, and k is the energy barrier for the non-radiative transition. B Let η be the Boltzmann constant, T be the temperature, A be a certain constant, η be the luminous efficiency, I0 be the luminous intensity at room temperature (25℃), and I(T) be the luminous intensity at temperature T.

[0064] Dorenbos et al. are studying photoluminescence in Eu... 2+ In the thermal quenching mechanism of doped phosphors, it is believed that Eu 2+ The excited-state 5d electrons are thermally ionized into the matrix conduction band, and then nonradiatively recombine elsewhere to return to the ground state. For example... Figure 1 As shown, in Eu 2+ In doped phosphors, the activation energy is the band gap difference between the lowest 5d band and the conduction band bottom. He assumes the probability of thermally induced nonradiative transitions is 3 × 10⁻⁶. 13 Hz (phonon energy is 1000 cm⁻¹) -1 Eu 2+ 4f 6 5d 1 →4f 7 The radiation probability is 1.1 × 10⁻⁶. 6 Hz; from this, he summarized the following relationship between thermal activation energy and quenching temperature (the temperature at which the luminescence intensity decreases to half of its low-temperature value):

[0065]

[0066] Currently, the thermal quenching performance of phosphors is mainly determined experimentally; there are no relevant studies or patents, and predictions are only made using theoretical calculations. Taking the red phosphor SrLiAl3N4:Eu as an example... 2+ For example, Alexander Moewes' team used SLAN:Eu phosphor thermal quenching data to obtain the thermal activation energy ΔE = 0.28 eV by fitting formula (2); then they used resonant inelastic X-ray scattering technology to determine the 5d-CB bandgap difference ΔE. eC It is 0.2±0.1eV.

[0067] In their research, the luminescence intensity only decreased to 95% of room temperature when the temperature reached 200℃, indicating that the thermal activation energy is insufficient to explain the excellent thermal stability of this phosphor. Clearly, the quenching temperature Tquenching summarized by Dorenbos and measured experimentally is insufficient. 0.5 The thermal activation energy obtained by reverse calculation is not equivalent to the thermal activation energy ΔE obtained by fitting formula (2). Furthermore, Jia Yongchao obtained the SrLiAl3N4:Eu... 2+ The thermal activation energies at the two sites of the phosphor are 2.727 eV and infinity, respectively. This further demonstrates that the thermal quenching activation energy is insufficient to characterize the phosphor SrLiAl3N4:Eu. 2+ Its luminescence and thermal stability properties.

[0068] Based on this, this patent proposes a method for evaluating the thermal quenching performance of phosphors using theoretical calculations. The method primarily employs a single luminescent central ion to replace specific lattice sites to construct a phosphor model. Then, the lattice thermal conductivity of the phosphor model is calculated using first-principles methods of density functional theory. Finally, by comparing the lattice thermal conductivity of similar models of currently commercially available phosphors, it is determined whether the phosphor prepared by doping the target crystal possesses excellent thermal quenching performance. This invention, through theoretical calculations, can significantly save time and trial-and-error costs, greatly reducing the development cost of commercial phosphors and improving efficiency.

[0069] The following section details the method for screening phosphor materials with excellent resistance to thermal quenching.

[0070] like Figure 2 This invention provides a method for screening phosphor materials with excellent resistance to thermal quenching, comprising the following steps:

[0071] (1) Construction of the phosphor model:

[0072] Obtain the crystal structure of the matrix and determine the lattice sites of the crystal structure;

[0073] A series of phosphor models were constructed by replacing the lattice sites with luminescent centers;

[0074] (2) Calculate the lattice thermal conductivity of the phosphor model:

[0075] The lattice thermal conductivity and electronic structure of the series of phosphor models were calculated using first-principles calculations;

[0076] (3) Experimental comparison and verification:

[0077] The series of phosphor models were initially screened based on the calculated electronic structure to obtain a series of phosphor models with luminescent properties.

[0078] The lattice thermal conductivity of the series of phosphor models initially screened was compared to select phosphor models with excellent resistance to thermal quenching.

[0079] For the construction of the phosphor model in step (1):

[0080] For constructing phosphor models, a high-concentration model can be used, where a single luminescent center replaces a suitable lattice site in the matrix. The replacement of a suitable lattice site with a single luminescent center primarily considers the degree of matching between the luminescent center (e.g., rare earth ions, transition metal ions, etc.) and the matrix, mainly from two aspects: first, electroneutrality, meaning the valence state of the luminescent center atom is consistent with the valence state of the suitable lattice site in the matrix, such as in the phosphor Sr. 1-x LiAl3N4:xEu 2+ If it differs from its matrix SrLiAl3N4, charge compensation needs to be considered; secondly, elemental size needs to be considered, such as the Eu content in the phosphor in the example above. 2+ Sr in its matrix 2 + The sizes are about the same.

[0081] In some preferred embodiments, the matrix is ​​any one of nitrides, halides, oxides, nitrogen oxides, silicates, and phosphates.

[0082] In some preferred embodiments, the luminescent center is a rare earth ion or a transition metal ion.

[0083] In some preferred embodiments, the rare earth ion is Ce. 3+ 、Nd 3+ Dy 3+ Eu 2+ Eu 3+ Pr 3+ Any one of the following; the transition metal ion is Cr 3+ Mn 2+ Pb 2+ Any one of them.

[0084] In a preferred embodiment, the lattice sites of the crystal structure are lattice sites that can be replaced by luminescent centers.

[0085] In a preferred embodiment, the molar percentage of doped luminescent centers in the series of phosphor models is 0.01% to 30%. Examples include 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, and 30%. This invention constructs phosphor models with concentrations higher than actual concentrations. Using high-concentration phosphor models is to save computational resources and match current computing power. Experimentally, the concentration of europium-doped rare-earth luminescent materials is only a few percent, or even a fraction of a percent. In subsequent embodiments, this invention uses the Sr phosphor model... 0.75 LiAl3N4:0.25Eu 2+ Let's take the example of its actual doping concentration, which is usually around 2%, to explain in detail.

[0086] In some preferred embodiments, the process of constructing a series of phosphor models further includes:

[0087] The elements of the lattice sites and the luminescent centers are compared and analyzed to ensure that the lattice sites match the luminescent ions.

[0088] In some preferred embodiments, the condition for ensuring that the lattice sites match the luminescent ions is:

[0089] The elements of the lattice sites match the size of the luminescent centers; and

[0090] The elements at the lattice sites are in charge balance with those at the luminescent centers.

[0091] In this embodiment of the invention, the size matching means that the ionic radius of the substituted element is approximately the same as the radius of the substituted element.

[0092] When the elements at the lattice sites are not in charge with the charge of the luminescent centers, charge compensation is performed to ensure that the charge balance of the constructed series of phosphor models is maintained.

[0093] In a preferred embodiment, the method for charge compensation is one of vacancy, interstitial doping, and asymmetric charge substitution;

[0094] The vacancy doping utilizes cation vacancies to balance the charge.

[0095] The interstitial doping utilizes anion interstitial doping to balance the charge.

[0096] The asymmetric charge substitution is achieved by using unequal-valence ions to balance the charge.

[0097] In a preferred embodiment, the vacancy cation used in the vacancy is Li. + ;

[0098] The anion used in the interstitial doping is X. - X is a halogen;

[0099] The cation used in the asymmetric charge substitution is Mg. 2+ In asymmetric charge substitution, anion balance can also be used to maintain electroneutrality. The anion used in asymmetric charge substitution is O. 2- The ions used for balancing charge in different charge compensation methods can be selected according to actual conditions; this invention does not limit the specific ion to Li. + X - Mg 2+ O 2- .

[0100] In this embodiment of the invention, when there is a charge imbalance, methods such as vacancy doping, interstitial doping, or asymmetric charge substitution are considered for charge compensation to ensure charge balance. For example, when the matrix SrLiAl3N4 is doped with the luminescent center element Ce... 3+ When there is a charge imbalance, 1) Mg can be used 2+ Balanced electroneutrality, meaning the phosphor can be Sr 0.75 Li(Al 2.75 Mg 0.25 N4: 0.25Ce 3+ Of course, electroneutrality can also be balanced using anions, such as the CaO in phosphors. 0.75 Si(O 2.75 N 0.25 ):0.25Ce 3+ ;2) Li can also be used + Vacancies balance electroneutrality, meaning the phosphor can be Sr 0.75 Li 0.75 Al3N4:0.25Ce 3+ ;3) Halogen X can also be used - Interstitial doping balances electrical neutrality, meaning the phosphor can be Sr. 0.75 LiAl3N4X 0.25 0.25Ce 3+ wait.

[0101] For step (2), the lattice thermal conductivity of the phosphor model is calculated as follows:

[0102] This step primarily involves calculating the lattice thermal conductivity of the phosphor model using first-principles methods of density functional theory.

[0103] In a preferred embodiment, the specific method for calculating the lattice thermal conductivity of the series of phosphor models using first-principles calculations is as follows:

[0104] The series of phosphor models were structurally optimized based on first-principles calculations to obtain an optimized crystal structure.

[0105] The force constants are obtained by moving atoms to calculate the forces acting on the atoms in the optimized crystal structure.

[0106] The force constant is processed to obtain the lattice thermal conductivity of the phosphor model.

[0107] In this invention, the method for obtaining thermal conductivity is calculated using software. The software used includes two types: one is software for calculating the forces acting on structural optimization and atomic movement, including PWSCF, SIESTA, VASP, CASTEP, ABINIT, and WIEN2K; the other uses density functional perturbation theory to calculate the atomic force constants, with a convergence criterion of 10 for the total electron energy. -8 eV; another type is software that processes force constants to obtain phonon band structure, density of states, and lattice thermal conductivity, including phonopy, phono3py, and ShengBTE, which use a smearing method with SIGMA of 0.1 instead of the linear tetrahedral method.

[0108] In some preferred embodiments, the specific method for obtaining the lattice thermal conductivity of the phosphor model is as follows:

[0109] 1) Structural optimization: Theoretical calculations are based on first-principles calculations, and the exchange-correlation functional is performed using the GGA-PBE method. Furthermore, calculations for all systems containing d and f orbital electrons consider LSDA+U. eff The range is 0 to 10 eV, for example, using U eff =2.5eV to handle strongly correlated Eu 4f electrons. During structure optimization, the convergence criteria for total electron energy and atomic forces are set to 10. -5 eV and A step-by-step convergence method can be adopted to reach the convergence criterion, and a quasi-Newton algorithm can be used for self-consistent computation. The minimum distance between the K points sampled in the first Brillouin zone is... The generated grid is centered at the gamma point.

[0110] 2) The force constant is calculated by moving atoms to determine the forces acting on them. The distance the atom is moved when calculating the second-order force constant is... The distance the atom is moved when calculating the third-order force constant is: The convergence criterion is the total electron energy 10. -8 eV.

[0111] 3) Calculate the lattice thermal conductivity using force constant processing software such as phono3py or ShengBTE. The minimum distance between the K points sampled in the first Brillouin zone is... The generated grid is centered at the gamma point.

[0112] For the experimental comparison and verification in step (3):

[0113] This step primarily involves comparing the lattice thermal conductivity of similar models of currently commercially available phosphors to determine whether the phosphor prepared by doping the target crystal possesses excellent thermal quenching performance. This invention, through theoretical calculations, can significantly save time and trial-and-error costs, greatly reducing the development cost of commercial phosphors and improving efficiency.

[0114] In a preferred embodiment, the criteria for selecting a phosphor model with excellent resistance to thermal quenching are:

[0115] Lattice thermal conductivity ≥ 0.6 W / (m·K).

[0116] In a preferred embodiment, it further includes:

[0117] The lattice thermal conductivity of existing phosphors corresponding to the matrix was calculated using first-principles calculations.

[0118] The lattice thermal conductivity of the initially screened series of phosphor models was compared with that of existing phosphors to screen out phosphor models with excellent resistance to thermal quenching.

[0119] In this invention, a high-concentration phosphor model is used to save computational resources and match current computing capabilities. Calculating the thermal conductivity of a crystal requires calculating the third-order force constants between atoms, a process that typically consumes a significant amount of computing time and demands powerful machines for processing these force constants. Using a high-concentration phosphor model greatly reduces computing time, and the force constants can be processed by computers with moderate capabilities. Furthermore, the first-principles calculation method allows for the theoretical exploration of whether the phosphor possesses luminescence capabilities, while also enabling the prediction of the phosphor's thermal quenching performance in advance. This significantly reduces experimental trial-and-error costs, conserves materials, and improves the development cost and efficiency of commercial phosphors. Specific Implementation

[0121] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0122] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0123] Unless otherwise specified, the methods described in the following embodiments are conventional methods; the reagents and materials mentioned are commercially available unless otherwise specified.

[0124] This invention first constructs a simplified phosphor model, and then calculates the lattice thermal conductivity of the phosphor model using density functional theory (DFT) and first-principles methods to evaluate its thermal quenching performance when prepared as a phosphor. A flowchart illustrating the process of evaluating / predicting the thermal quenching performance of phosphors is shown below. Figure 2 .

[0125] like Figure 2 As shown, a method for screening phosphor materials with excellent resistance to thermal quenching includes the following steps:

[0126] (1) Construction of the phosphor model

[0127] First, a suitable matrix crystal structure is selected.

[0128] Identify the crystal structure of the object to be evaluated from a crystal library. The crystal structure is typically that of a compound, such as a nitride, oxide, or nitrogen oxide.

[0129] Secondly, determine which sites in the crystal structure can be replaced by luminescent center elements / ions.

[0130] The lattice sites of the crystal structure can be co-occupied sites or single lattice sites. Substitution sites primarily consider the charge balance between the substituted element and the luminescent ion; vacancies can also be used to achieve electroneutrality of the crystal. The luminescent center element / ion can be a rare earth ion or a transition metal ion; an example of a rare earth ion is Ce. 3+ 、Nd 3+ Dy 3+ Eu 2+ Pr 3+ Examples of transition metal ions include, for example, chromium ions, manganese ions, and lead ions.

[0131] Finally, a simplified model of replacing a phosphor at a specific site with a single luminescent ion in a single cell / supercell.

[0132] The construction of phosphor models mainly considers the degree of matching between the luminescent centers (such as rare earth ions, transition metal ions, etc.) and the matrix. This is primarily considered from two aspects: first, electroneutrality, meaning the valence state of the luminescent center atoms matches the valence state of suitable lattice sites in the matrix, such as in the case of Sr phosphors. 1-x LiAl3N4:xEu 2+ If it differs from its matrix SrLiAl3N4, vacancy compensation needs to be considered; secondly, elemental size needs to be considered, such as the Eu content in the phosphor in the example above. 2+ Sr in its matrix 2+ The sizes are about the same.

[0133] Due to the limitations of current computing resources and capabilities, this invention constructs a phosphor model with a higher concentration than the actual concentration. Experimentally, the concentration of europium-doped rare-earth luminescent materials is only a few percent, or even a fraction of a percent. Here, we use the Sr phosphor model... 0.75 LiAl3N4:0.25Eu 2+ Taking the actual doping concentration, which is typically around 2%, as an example, this invention utilizes the electronic structure obtained from DFT calculations as the basis for whether the phosphor can emit light. This requires that the energy bands of the substituted elements in its electronic structure are located in the band gap or at the bottom of the conduction band, using SrSiN2:Eu as an example. 2+ For example, Figure 3 The left bandgap is the Eu 4f bandgap, and the middle bandgap is the Eu 4f bandgap.

[0134] (2) Calculate the lattice thermal conductivity of the phosphor model.

[0135] First, the crystal force constant is calculated using software; then, the thermal conductivity is calculated using force constant processing software. The software used to calculate the crystal force constant can be any of PWSCF, SIESTA, VASP, CASTEP, ABINIT, or WIEN2K, or other software can be selected depending on the requirements. The force constant processing software can be any of phono3py or ShengBTE, or other software can be selected depending on the requirements.

[0136] The following explains the parameters used in the calculation process.

[0137] First, there is structural optimization. All our DFT calculations are performed using VASP software, employing the projected plane wave method and considering exchange-correlation effects using the Perdew-Burke-Ernzerhof (PBE) parameterized generalized gradient approximation (GGA).

[0138] With SrLiAl3N4:Eu 2+For example, the basis sets of Sr, Li, Al, N, and Eu atoms are 4s. 2 4p 6 5s 2 1s 2 2s 1 3s 2 3p 1 2s 2 2p 3 and 4f 7 5s 2 5p 6 6s 2 The cutoff energy of the plane wave basis set is 520 eV. The first Brillouin zone is integrated using the tetrahedral method modified by Bloch. The minimum distance between the K sampling points in the first Brillouin zone is... The generated mesh is centered at the gamma point. A self-consistent calculation is performed using the quasi-Newton algorithm embedded in VASP. The convergence criteria for total electronic energy and atomic force are set to 10. -5 eV and

[0139] During the calculations, errors occurred for some materials due to overly stringent initial convergence conditions during the self-consistent convergence process. To achieve our set convergence criteria for total electron energy and atomic force, we adopted a stepwise convergence method: first relaxing the convergence criteria, then gradually tightening them until the set convergence criteria were met. The minimum distance between the K points sampled in the first Brillouin zone is... The generated mesh is centered at the gamma point. The quasi-Newton algorithm embedded in VASP is used for structure optimization. The LSDA+U method (U...) is employed. eff =2.5eV) to treat strongly correlated Eu 4f electrons.

[0140] Regarding the handling of the force constant, this invention uses Phono3py as an example, and software such as ShengBTE can also be used to calculate phonon anharmonic properties and lattice thermal conductivity. This software provides two methods for calculating lattice thermal conductivity: one is the relaxation time approximation method, abbreviated as RTA; the other is the method of directly solving the linearized phonon transport Boltzmann equation, abbreviated as the direct method.

[0141] The parameters for the RTA method are set as follows.

[0142] The second-order term of the crystal potential energy is used to calculate atomic vibrations, and the third-order anharmonic term is used to calculate lattice thermal conductivity. The third-order force constants of all matrices and phosphors are expressed in the unit cell with finite atomic displacements. The calculations yielded the result, where the minimum distance between the K sampling points in the traditional Brillouin zone is [value missing]. Furthermore, the generated mesh is centered at the gamma point. When calculating the lattice thermal conductivity, the Brillouin zone is... The integration is performed by dividing the unit by the reciprocal of the lattice parameter to form a K-point grid. To obtain a more accurate atomic force constant, the convergence criterion for the total energy is 10. -8 eV.

[0143] Since the computational workload of the direct method for calculating thermal conductivity is much greater than that of the previous method, the parameter settings in the calculation of the force constant are consistent with the RTA method. Furthermore, the default method in Phono3py is selected to directly solve the phonon transport Boltzmann equation to obtain the thermal conductivity. The specific parameters are existing technology and will not be elaborated here.

[0144] (3) Experimental comparison and verification

[0145] A crystal structure model with high thermal conductivity was selected, and luminescent ion-doped inorganic compound phosphors were prepared using experimental methods to verify the luminescent performance and thermal quenching resistance of the phosphors.

[0146] Based on the above, the calculated thermal conductivity data of the phosphor model are shown in Table 1.

[0147] Evaluation criteria:

[0148] Excellent: Thermal quenching resistance ≥90%; Thermal conductivity ≥0.6 W / (m·K)

[0149] Good: 85% ≤ thermal quenching resistance <90%; 0.6 W / (m·K) ≥ thermal conductivity ≥0.3 W / (m·K)

[0150] Generally: 60% ≤ thermal quenching resistance ≤ 85%; 0.1 W / (m·K) ≤ thermal conductivity ≤ 0.3 W / (m·K)

[0151] Poor: resistance to thermal quenching <60%; thermal conductivity ≤0.1W / (m·K).

[0152] Table 1 SrLiAl3N4:Eu 2+ Sr2Si5N8:Eu 2+ and SrSiN2:Eu 2+ thermal conductivity

[0153]

[0154] Note: SrLiAl3N4:Eu 2+ -1 indicates the luminescent center ion Eu. 2+ Replaces the position at Sr1.

[0155] SrLiAl3N4:Eu 2+ -2 indicates the luminescent center ion Eu. 2+ Replaced at the Sr2 position. Sr2Si5N8:Eu 2+-1 indicates the luminescent center ion Eu. 2+ Replaced at the Sr1 position. Sr2Si5N8:Eu 2+ -2 indicates the luminescent center ion Eu. 2+ Replaced at the Sr2 position. SrSiN2:Eu 2+ Eu, representing the luminescent central ion 2+ Unreplaced. The heat quenching resistance is measured as a percentage of the luminous intensity at 200°C compared to that at room temperature.

[0156] The results in Table 1 show that the thermal quenching performance of the phosphors is ranked as follows: SrLiAl3N4:Eu 2+ Superior to Sr2Si5N8:Eu 2+ And it is superior to SrSiN2:Eu 2+ The order is consistent with the order of thermal conductivity.

[0157] In summary, the method provided in the above embodiments of the present invention mainly employs a single luminescent central ion to replace specific lattice sites to construct a phosphor model, and then calculates the lattice thermal conductivity of the phosphor model using first-principles methods of density functional theory. Finally, by comparing the lattice thermal conductivity of the crystal structure model, it is determined whether the phosphor prepared by doping the target crystal possesses excellent thermal quenching performance. Of course, it can also be compared with similar models of currently commercially available phosphors to screen for phosphors with excellent thermal quenching performance. The theoretical calculation method of the present invention can significantly save time and trial-and-error costs, greatly reducing the development cost of commercial phosphors and improving efficiency.

[0158] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for screening phosphor materials with excellent resistance to thermal quenching, characterized in that, Includes the following steps: The crystal structure of the matrix is ​​obtained, and the lattice sites of the crystal structure are determined; the luminescent centers are used to replace the lattice sites to construct a series of phosphor models; The lattice thermal conductivity and electronic structure of the series of phosphor models were calculated using first-principles calculations; The series of phosphor models were initially screened based on the calculated electronic structure to obtain a series of phosphor models with luminescent properties. The lattice thermal conductivity of the initially screened series of phosphor models was compared to select phosphor models with excellent resistance to thermal quenching.

2. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 1, characterized in that, The process of constructing a series of phosphor models also includes: The elements of the lattice sites and the luminescent centers are compared and analyzed to ensure that the lattice sites match the luminescent centers.

3. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 2, characterized in that, The condition for ensuring that the lattice sites match the luminescent centers is: The elements of the lattice sites match the size of the luminescent centers; and The elements at the lattice sites are in charge balance with those at the luminescent centers.

4. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 3, characterized in that, When the elements at the lattice sites are not in charge with the charge of the luminescent centers, charge compensation is performed to ensure that the charge balance of the constructed series of phosphor models is maintained.

5. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 4, characterized in that, The methods for charge compensation include vacancy, interstitial doping, and asymmetric charge substitution. The vacancy is achieved by utilizing cation vacancies to balance the charge. The interstitial doping utilizes anion interstitial doping to balance the charge. The asymmetric charge substitution is achieved by using unequal-valence ions to balance the charge.

6. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 1, characterized in that, The matrix is ​​any one of nitrides, halides, oxides, nitrogen oxides, silicates, and phosphates; The luminescent center is a rare earth ion or a transition metal ion.

7. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 6, characterized in that, The rare earth ion is Ce. 3+ 、Nd 3+ Dy 3+ Eu 2+ Eu 3+ Pr 3+ Any one of them; The transition metal ion is Cr. 3+ Mn 2+ Pb 2+ Any one of them.

8. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 1, characterized in that, The criteria for selecting phosphor models with excellent resistance to thermal quenching are: Lattice thermal conductivity ≥ 0.6 W / (m·K).

9. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 1, characterized in that, Also includes: The lattice thermal conductivity of existing phosphors corresponding to the matrix was calculated using first-principles calculations. The lattice thermal conductivity of the initially screened series of phosphor models was compared with that of existing phosphors to screen out phosphor models with excellent resistance to thermal quenching.

10. The method for screening phosphor materials with excellent resistance to thermal quenching according to claim 1, characterized in that, The specific method for calculating the lattice thermal conductivity of the aforementioned series of phosphor models using first-principles calculations is as follows: The series of phosphor models were structurally optimized based on first-principles calculations to obtain an optimized crystal structure. The force constants are obtained by moving atoms to calculate the forces acting on the atoms in the optimized crystal structure. The force constant is processed to obtain the lattice thermal conductivity of the phosphor model.

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