Study On The Luminescence Characteristics Of A Novel Electron Trapping Infrared To Visible Light Silicate Photoconversion Material

Electron trapping materials （ETM） have the property of photoconversion, and itis called the photostimulated luminescence materials in the field of luminescence.This kind of material has been always focused on extensively since it was firstmentioned by Lindmayer from USA in1986. It has extensive application prospect oninfrared detection, optical storage, infrared conversion and X-ray imaging. While thephotostimulated luminescence materials are irradiated by light, the electron （or hole）is captured by trap being in a comparative stable state. As it is stimulated by infraredlight or others, the electron （or hole） is released to produce photostimulatedluminescence （PSL）. At present, the commercial ETM is main alkaline sulfides, whohave many advantages such as intense initial PSL intensity, high PSL light storagecapacity. However, the fatal disadvantage of alkaline sulfides is their poor chemicalstability. The more import is that the toxic substance will arise once the sulfides breakdown, and it will cause serious circumstance pollution. To solve this problem,searching an ETM with good chemical stability is the focus for study on ETM.Silicates have good chemical stability, thermostability and resistance to corrosion.It is used as the host of rare earth luminescence material extensively now. Sr₃SiO₅:Eu²⁺is a traditional LED （light emitting diodes） phosphor, which can absorb UV-lightand blue-green light to emit in yellow peaked at580nm. In this paper, we research theSr₃SiO₅: Eu²⁺in the form of co-doping another coactivator to enhance the PSLproperty. The key results of researching are as follows: 1) We have researched the effect on the PSL properties by co-doping thecoactivators in lanthanide （La、Ce、Pr、Nd、Sm、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu） into Sr_2.99SiO₅:0.01Eu²⁺. It is found that the sample co-doping Tm³⁺hasthe best PSL property. The initial PSL intensity and PSL light storage capacity isimproved at different extent. The reason is that a new trap （trap B） is arised in thesample co-doping Tm³⁺, and the trap could greatly enhance the PSL property ofmaterial.2) We have researched the variation of PSL properties of Sr_2.99SiO₅:0.01Eu²⁺withdifferent level of co-doping Tm³⁺. The initial PSL intensity and PSL light storagecapacity of ETM reached the maximum at the Tm³⁺concentration of0.0004. Theinitial PSL intensity is33times of the Tm³⁺free sample and the PSL light storagecapacity is2times of the Tm³⁺free sample. It is shown that this kind of ETM hasbroad application prospect in the field of infrared detection. The quantity of trapB also reaches the maximum when the Tm³⁺concentration is0.0004, it is impliedthat the intense relationship between the PSL property and the quantity of trap B.3) The rules for electron transition of trap A and trap B in Sr_2.9896SiO₅:0.01Eu²⁺,0.0004Tm³⁺have been studied. During the arrangement and analysis of data, it isconcluded that there are tow kinds of trap A and B, and the essential difference isthe distance between them and luminescence centre Eu²⁺. The first kind of trap isnear from Eu²⁺, the electron in trap is easy to perform charge transition betweenthe electron and Eu²⁺ground level. In the condition of thermostimulation, theelectron in trap could convert to photon emitting thermoluminescence yet,nevertheless, with photostimulation, the electron in trap will cause non-irradiationtransition. The second kind trap is far from Eu²⁺, and the electron in trap willconvert to photon in the stimulation of thermal or luminescence. The electron inthe second kind of trap A will release slowly without intense PSL, and theelectron in the second kind of trap B will release rapidly to produce intense PSL.Meanwhile, it is found that the electron released from trap A could be retrappedby trap B in the process of phosphorescence decay. It is the effect of electronretrapping by trap B.4) The effect on the characteristics of photoluminescence （PL）, phosphorescenceand PSL of Sr_2.9896SiO₅:0.01Eu²⁺,0.0004Tm³⁺doped Ba has been researchedtentatively. The emission peaks of PL, phosphorescence and PSL are all redshifted gradually as the Ba content is increased. The reason is that the latticeparameter of material is changed to make the Eu²⁺5d orbital decrease afterdoping Ba. The properties of phosphorescence and PSL of the material are decreased evidently as the Ba content is increased. The trap A and trap B inphosphors are both destroyed after doping Ba, and a new trap （trap A-B） isemerged. However, the new trap could not enhance the phosphorescence or thePSL at all.