Preparation And Photoluminescence Properties Of Dy³⁺/Tm³⁺ Doped Galliosilicate Phosphors And Glass

In recent years,the mainstream design scheme of W-LED in the market is to use blue LED chips combined with yellow phosphor(YAG:Ce³⁺)packaging to achieve white light illumination.However,there are still some inherent defects,such as a relatively high color temperature（CCT>5600 K）,and the susceptibility of blue light LED chips to driving voltage,resulting in color coordinate drift,limiting the application range of this type of white light LED.Therefore,a new trend is to achieve white light emission under ultraviolet（UV）LED excitation to exclude the participation of Ga N-based blue LED chips,which can avoid color shift during use.Therefore,it is of great significance to study a new type of efficient UV excitation single substrate color adjustable white light illumination.In this paper,using Ca₃Nb Ga₃Si₂O₁₄（referred to as CNGS）as the substrate and Dy³⁺and Tm³⁺as the luminescent centers,the preparation methods and luminescent properties were studied.Through component control,a phosphor and glass-ceramics that can achieve tunable luminescent color were successfully prepared,and their systematic research was carried out.The main work of this paper is as follows:（1）A novel single-phase white light emitting material,Ca₃Nb Ga₃Si₂O₁₄:Dy³⁺/Tm³⁺was synthesized by high-temperature solid-state method.The structure of the material was characterized by X-ray diffraction（XRD）,and the luminescence properties were measured using an Edinburgh spectrometer.The general rule of the fluorescence spectrum changing with the concentration of doped rare earth ions was summarized.In Ca₃Nb Ga₃Si₂O₁₄:0.03Dy³⁺/y Tm³⁺phosphors,the effective excitation ranges are 365 nm and 352 nm.By adjusting the Tm³⁺doping concentration,not only the optimal luminescence intensity but also the tunable luminescence color are achieved.There is an overlap region between the emission spectra of Tm³⁺doped phosphors and the excitation spectra of Dy³⁺doped phosphors,indicating that there is an energy transfer between Tm³⁺and Dy³⁺.By adjusting the doping concentration of Tm³⁺,Ca₃Nb Ga₃Si₂O₁₄:0.03Dy³⁺/y Tm³⁺phosphors can achieve white light emission;When y=0.04,the chromaticity coordinates are（0.3315,0.3382）,which are closest to the standard white light point,and the relevant color temperature is 5541 K.The research results show that Ca₃Nb Ga₃Si₂O₁₄:Dy³⁺/Tm³⁺phosphors have good potential application value in the field of white LED lighting.（2）A series of color adjustable Ca CO₃-Nb₂O₅-Ga₂O₃-Si O₂glass ceramics activated by Dy³⁺and Dy³⁺/Tm³⁺ions were prepared by traditional melt crystallization methods.The structure,energy transfer（ET）,and photoluminescence（PL）characteristics of the glass ceramics were studied.The preparation conditions,phase composition,morphology,transmittance,optimal heat treatment conditions,and luminescent properties of glass-ceramics were studied by using DTA,XRD,SEM,and UV-vis photometer techniques.The results show that the optimal heat treatment process for obtaining transparent and well formed glass-ceramics is to crystallize at820℃for 5 hours.The luminescence color can be adjusted by adjusting the doping amount of Tm³⁺and changing the excitation wavelength.The results show that the Dy³⁺/Tm³⁺co-doped Ca CO₃-Nb₂O₅-Ga₂O₃-Si O₂glass ceramic has a color coordinate of（0.3324,0.3352）that is closest to the standard white light（0.333,0.333）and a related color temperature of 5502 K under excitation of 365 nm.This indicates that this glass ceramic has a promising application prospect in WLED devices.（3）The effect of crystallinity on luminescence in microcrystalline glass was calculated.The crystallinity of microcrystalline glass for 2.5,5,and 7.5 hours was calculated to be 1.88%,5.44%,and 23.96%,respectively.The higher the relative crystallinity in microcrystalline glass,the higher the luminescence intensity.The internal quantum efficiency of Dy³⁺doped CNGS phosphor,glass powder,and microcrystalline powder was tested to be 13.3%,8.5%,and 5.9%,respectively.The internal quantum efficiency of the samples obtained in this work is low,and needs to be improved.Stark splitting occurs at the ⁴F_9/2→⁶H_13/2and ⁴F_9/2→⁶H_15/2positions of Dy³⁺ions in phosphors,while the emission peaks of Dy³⁺ions in doped glass powders and microcrystalline glass powders are degenerate,showing only one emission peak.This is mainly due to the special structure of glass with long range order and short range disorder.The fluorescence lifetime of Dy³⁺in double doping is shorter than that in single doping,which is mainly caused by the energy transfer between Dy³⁺ions and Tm³⁺ions.The energy transfer efficiency in fluorescent powder,glass powder,and microcrystalline glass powder was calculated to be 15.2%,39.9%,and 37.4%,respectively.