Research And Application Of Luminescence Properties Of Color-tunable MBaB₉O₁₅:Eu²⁺（M=Na/Li） Borate Phosphors

In this paper,LiBaB₉O₁₅ and NaBaB₉O₁₅ borate materials with[B₃O₇]^5- polyanion are selected as the research objects.A series of new color-tunable and performance controllable LiBa_1-xB₉O₁₅:xEu²⁺and NaBa_1-xB₉O₁₅:xEu²⁺phosphors are synthesized by solid-state reaction based on controlling the concentration of the activator and the strength of the reducing atmosphere,without changing the chemical composition of the matrix.The effects of different reducing atmospheres on crystal structure,particle morphology,element distribution,luminescence dynamics,steady-state spectra,thermoluminescence spectra,Eu²⁺ion local environment,defect distribution and trap depth were studied in detail.A comprehensive explanation of the effects of different reducing atmospheres on the luminescence performance,and the influence of different reducing atmospheres on the luminescence properties was fully revealed.The specific research results are as follows:（1）Select LiBaB₉O₁₀ as the matrix material and rare earth ion Eu²⁺as the luminescence center,a color-tunable LiBa_1-xB₉O₁₅:xEu²⁺（0.015≤x≤0.09）phosphors are prepared by changing the Eu²⁺concentration.The emission spectra result show that with the increase of Eu²⁺concentration,the emission peak position firstly red-shifted from 545 nm（x=0.015）to 593 nm（x=0.03）,and then blue-shifted to 388 nm（x=0.09）,realizing continuous tunable of the emission spectra.Explain the change of emission spectra through Stokes shift and crystal field splitting.The temperature-dependent emission spectra show that the integrated intensities of sample can be maintained at 91%（@150 ℃）of initial intensity at room temperature,which show high thermal stability.（2）Starting from the experimental conditions,a new color and performance tunable NaBaB₉O₁₅:0.02Eu²⁺phosphors were synthesized by changing the reducing atmosphere.The results of X-ray diffraction,scanning electron microscopy and element distribution diagrams show that pure phase phosphors are synthesized under different reducing atmospheres,and the elements in the particles are uniformly distributed.The emission spectrum results show that the sample synthesized in a weak reducing atmosphere has one more emission band than the sample prepared in a strong reducing atmosphere.By analyzing the excitation spectrum,fluorescence lifetime and electron paramagnetic resonance spectrum,it is found that the local environment of Eu²⁺is different under different reducing atmospheres.Further testing of the thermoluminescence spectra,showing that the samples obtained under a weak reducing atmosphere have shallow traps and deep traps,while the samples obtained under a strong reducing atmosphere have only shallow traps.These results show that the possible reason for the increase of the luminescence intensity and color adjustability of the phosphor may be the appearance of defects.（3）Further study the blue-cyan NaBa_1-xB₉O₁₅:xEu²⁺（0.02≤x≤0.06） phosphors under weak reducing atmosphere.As mentioned above,the NaBa_1-xB₉O₁₅:xEu²⁺（0.02≤x≤0.06）phosphor has two emission bands,which is confirmed by Gaussian fitting.The steady-state spectrum and the transient spectrum are analyzed to confirm this result.More importantly,the maximum internal quantum yield of the phosphor is determined to be～95.2%.At the same time,temperature-dependent emission spectra result reveal that at 150°C,the integrated intensity of the phosphor remains at 96%of room temperature,which shows good thermal stability and high quantum yield.