Research On The Luminescence Properties And Application Of Multiple Activator Ions In Ba₂LaF₇ Glass-ceramics

Luminescent materials doped with lanthanide ions have been drawing spectacular attention in consideration of their potential application in lighting,biomedical imaging,anti-counterfeiting,temperature sensing,solar cells,data storage and 3D display,duing to their strong light absorption,high color purity,bright color,wide range of emission wavelength coverage,and stable physical and chemical properties.Recently,luminescent glass doped with lanthanide ions have great potential applications in temp erature sensors,white LED devices and other directions for their high transparency,low cost and easy processing.Considering the oxy-fluoride glass ceramics not only have comparatively low phonon energy of fluorides,but also exhibit excellent chemical a nd physical stability related to oxides.Thus,the luminescent behavior of Ba₂LaF₇ glass ceramics with various activator ions and the potential application in photothermometers and high power white LED have been study and discuss in this study.（1）The potential applications of Ba₂LaF₇:Yb³⁺,Er³⁺glass ceramics in temperature sensors and photon heaters were explored.The Ba ₂LaF₇ nano-crystals embedded in SiO₂-Na₂O-AlO₃-BaF₂-LaF₃ transparent glass matrix were successfully prepared by the traditional melt-quenching method and subsequent heat treatment process in this study.The way to optimize the up-conversion luminescence properties of Er³⁺ions was explored by improving the heat treatment process of glass ceramics.After optimizing the experimental conditions,the temperature-depended fluorescence intensity ratio and thermal sensitivity of thermally coupled emitting states(⁴S_3/2,²H_11/2)behavior of Er³⁺ion was investigated under the excitation of 980 nm.The maximum thermal sensitivity was approxi mately 0.43%K^-1 in 298 K.Besides,the temperature of Ba₂LaF₇ glass ceramics rose from 336 to 407 K,when the laser pump power density increased from 1.01 to 9.59 W/cm².Moreover,the excellent thermal stability of the sample for temperature detection in t he range of 298-573 K was proved by measuring the fluorescence intensity ratio of the samples during the high temperature and low temperature cycle.The results indicate that the Ba ₂LaF₇:Yb³⁺,Er³⁺glass ceramics could be potential candidates for thermome ters and integrating heaters.（2）The up-conversion white light emission properties of Ba₂LaF₇:Yb³⁺,Er³⁺,Tm³⁺glass ceramics was investigated.A tuning luminous color and white light emission of Ba₂LaF₇ glass ceramics were realized by adjusting the doping concentration of rare earth ions.Fluorescence emission spectroscopy showed that the fluorescence emission of glass ceramics changed from blue to yellow to orange under980 nm excitation when the doping concentration increased from 20 to 80%of Yb³⁺ions.In addition,on the basis of Ba₂LaF₇:40Yb³⁺,1Er³⁺glass ceramics（yellow light emission）,the up-conversion white light emission was realized by tri-doping Tm³⁺ions.Moreover,the thermal stability of white light emission of Ba ₂LaF₇:40Yb³⁺,1Er³⁺,2Tm³⁺glass ceramics was studied.It was found that the CIE color coordinates（x=0.3920,y=0.2801）of the samples were still in the white light range at 573 K,indicating that the glass ceramics had high white light stability.（3）Based on the advantages of Ba₂LaF₇ glass ceramics,we further explored the down-conversion luminescence properties and the potential applications in high power white LED of Eu/Tb co-doped Ba₂LaF₇ glass ceramics.The silicate glass embedded with Ba₂LaF₇:35Eu³⁺/Eu²⁺,20Tb³⁺nano-particles by the self-crystallized growth in situ achieves a low scattering loss,high luminous efficiency,good thermal stability,and the spectral chromaticity coordinate of which locates in white region at573 K.Moreover,this glass ceramics keep high transparenc y under UV-Chip-On-Board（UV-COB）excitation after thermal aging for 384 h.Hence,a thermal stable organic-resin-free white LED device combined the self-crystallized Ba₂LaF₇:35Eu³⁺/Eu²⁺,20Tb³⁺glass ceramics with a UV-COB is demonstrated.Additionally,the cathodeluminescence spectra as a function of accelerating voltage and probe current indicate the excellent degradation resistance properties with good color stability of the glass ceramics.Our results demonstrate unambiguously that the self-crystallized Ba₂LaF₇:35Eu³⁺/Eu²⁺,20Tb³⁺glass ceramics could serve as a bi-functional promising candidate for high-power white LEDs and filed emission displays.