Effect Of Li⁺/Na⁺/K⁺doping On Up/Down Conversion Luminescence Of Bi₂O₃:Yb³⁺/Er³⁺and Y₂O₃:Tm³⁺ Phosphors

Rare earth luminescent materials attract great interest of many researchers for their low toxicity,high chemical stability,good biological suitability,long lifetime,high photostability,good thermal stability and tunable fluorescence emission wavelength.Rare earth luminescent materials have a wide range of applications,such as optical temperature sensing,biomedical imaging,anti-counterfeiting,lasers,displays,solar cells,solid-state lasers and fluorescent biomarkers,etc.However,they have low conversion efficiency in up conversion processes,and severely limited their applications.According to reports,the luminescence intensity of rare earth ions can be enhanced by doping with alkali metal ions（Li⁺,Na⁺,K⁺）to enhance the asymmetry of the crystal field around the rare earth ions.Doping with alkali metal ions can also enhance the emission intensity of rare earth luminescent materials by occupying gaps,grain boundaries or substitution sites.This paper focuses on the upconversion luminescence properties of Bi₂O₃:Yb³⁺,Er³⁺phosphors co-doped with alkali metal ions（Li⁺,Na⁺,K⁺）and the downconversion luminescence properties of Y₂O₃:Tm³⁺phosphors co-doped with Li⁺,Na⁺,K⁺ions.The main contents are as follows:（1）A series of Bi₂O₃:Yb³⁺,Er³⁺,Li⁺/Na⁺/K⁺phosphors were prepared by coprecipitation method.Under the excitation of 980 nm laser,Bi₂O₃:Er³⁺phosphor emits green light.The green to red tunable emission of the samples was achieved by doping the Bi₂O₃:Er³⁺phosphors with Yb³⁺ions.The Powder X-ray diffraction pattern indicated,the crystal phase of Bi₂O₃has being changed with the doping concentration of Yb³⁺ions increased.Under the excitation of 980 nm laser,doped with Li⁺,Na⁺and K⁺,Bi₂O₃:Yb³⁺,Er³⁺phosphors can increase the luminescence intensity of Er³⁺ion red light conversion at664 nm.Among these ions,the enhancement of K⁺ions is the best.Compared with the Bi₂O₃:Yb³⁺,Er³⁺phosphors doped with Li⁺and Na⁺ions,the intensity of red upconversion luminescence of Er³⁺ions is enhanced by about 4.6 times in the Bi₂O₃:Yb³⁺,Er³⁺phosphors doped with K⁺.（2）A series of Y₂O₃:Tm³⁺,Li⁺/Na⁺/K⁺phosphors were prepared by precipitation method.The results of X-ray powder diffraction analysis showed that the samples were all cubic phase Y₂O₃.The down-conversion luminescence intensity of Y₂O₃:Tm³⁺phosphor was enhanced by changing the type and concentration of alkali metal ion doping.Compared with the doped Li⁺ions and Na⁺ions,the K⁺ion doped Y₂O₃:Tm³⁺phosphor has the strongest down-conversion luminescence intensity.The luminescence intensity of the sample can be further enhanced with the increase of annealing temperature.