Preparation And Luminescent Properties Of Lutetium-based Oxide Luminescent Materials Excited By Near-ultraviolet And Blue Light

The advent of high-efficiency blue-light chips?LEDs?has made white LEDs an important way to obtain white light and developed into the fourth-generation lighting source.As a important optical conversion material in white LEDs,rare earth phosphors have become a hot topic in the research field.As the emission band of blue LEDs further expands to the near-ultraviolet region,matching phosphors are also being continuously developed.Most of the trivalent rare earth ions(Re³⁺)emit light from the intragroup transition of 4f-4f energy levels.Due to the shielding effect of the outer electrons of 4f orbits,the excitation and emission peaks are relatively less affected by the matrix,and the spectral characteristics are relatively fixed.Therefore,we locate the transition metal ion Cr³⁺and rare earth ion Ce³⁺in the transition between f-d groups,and study the change of optical properties reflected by the influence of the crystal field.It is also inferred the specific location by judging the strength of its crystal field environment.Mutual verification can not only improve the theoretical guidance of practice,but also explore new matrix materials to expand the type of phosphor.In addition,the preparation process of the green fluorescent ceramics missing in the field of high-power white LED is also explored.This paper is mainly carried out from the following four aspects:?1?We have developed a new blue phosphor SrLu₂O₄:Ce³⁺,which is well matched to 400nm near-ultraviolet LEDs and has excellent thermal stability.At 405 nm excitation,broadband blue light emission with a peak at 460 nm and a full width at half maximum of 90 nm is emitted.The optimized ion doping concentration of the sample obtained was optimized to have an internal quantum efficiency of 76%.At 150?,its emission intensity can still maintain 86%of the emission intensity at room temperature.White LED devices were obtained by coating on a 405 nm near-ultraviolet chips by mixing with a commercial yellow phosphor and a red phosphor.By adjusting the specific gravity of the components,the color temperature control can be adjusted within the range of 3094-8990K while maintaining a high color rendering index?Ra?90?.All of these characteristics indicate that SrLu₂O₄:Ce³⁺is a promising near-ultraviolet-excited white LED light-converting luminescent material.?2?Previously,in the Ce³⁺ion-activated SrLn₂O₄ type phosphor?Ln=Y,Lu,Sc,etc.?,only one luminescence center was exhibited,and it was blue light emission.In this chapter,we observed the second luminescence center of Ce³⁺in SrLu₂O₄:Ce?3+?.The illuminating center can emit a broadband red light emission with a peak at 600 nm under excitation of 485 nm.We believe that this new luminescent center?Ce?II??occupies the Lu³⁺position,while the blue illuminating center?Ce?I??is derived from the Sr²⁺position.Spectroscopic analysis shows that at low doping concentration,the Ce?I?luminescence center is preferentially formed,and the number of luminescence centers is significantly reduced compared with Ce?I?/Ce?II?as the Ce³⁺ion doping concentration increases.x reached 0.004.The fluorescence lifetime of the two luminescent centers was also measured as the doping concentration was changed,and the energy transfer from Ce?I?to Ce?II?was observed.When the temperature rises from 83K to 350K,the luminescence intensity of Ce?II?decreases at a faster rate than the Ce?I?center,indicating that the relative luminescence intensity ratio can be used to reflect the temperature change,and at 283K,The relative sensitivity is calculated to be as high as 2.28%K^-1.?3?The Ca₂LuZr₂Al₃O₁₂?CLZA?phosphor with Cr³⁺ion doped garnet structure is a promising broadband near-infrared phosphor with an excitation peak that perfectly matches the 460nm blue chip.Using this phosphor with a 460 nm blue LED package,an output of near-infrared light in the 750-850 nm range is obtained.Moreover,its electro-optic efficiency is 4.1%,which is better than the current conventional tungsten lamp efficiency?2.9%?.In the CLZA matrix structure,Cr3⁺occupies the Ca²⁺/Lu³⁺and Zr⁴⁺sites,forming two luminescent centers Cr1 and Cr2,respectively.For the CLZA:xCe³⁺,yCr³⁺ series of samples,Ce³⁺and Cr³⁺occupy the regular dodecahedral and regular octahedral positions,respectively,and calculate the crystal field strength of the two activated ions.Due to the inherent property of the weak absorption capacity of Cr³⁺,the absorption of near-ultraviolet light by the phosphor is increased by introducing Ce³⁺ions as a sensitizer,and the efficient energy transfer rate of Ce³⁺to Cr³⁺is calculated.When analyzing the temperature dependence of CLZA:Cr³⁺samples,it is found that there are two thermal processes in the heating process,which are low temperature thermal quenching and high temperature thermal ionization process,and the specific activation energy of the two processes is calculated and analysis.?4?High-power white LED/laser illumination is the development trend in the field of illumination,and fluorescent transparent ceramic is an important light conversion material in the field of high-power illumination.In view of the current research on fluorescent transparent ceramics,yellow light transparent ceramics are mainly used,and green light transparent ceramics has been a short board for research.Therefore,based on the previous preparation process of yellow transparent ceramic(YAG:Ce³⁺),we studied the preparation process of Ca₃Sc₂Si₃O₁₂:Ce³⁺-based green light transparent ceramics.First,for the more complex Ca₃Sc₂Si₃O₁₂2 sample,the path of first synthesizing the powder and then growing the crystal at a high temperature is adopted.The effects of the particle size distribution on the particle milling medium,ball milling time and ball milling speed were developed.The"optimum particle size distribution"under the current sintering conditions and the green ceramic sample with a linear transmittance of 14%were obtained.