Manipulating Trap Filling Of Persistent Phosphors Via Up-conversion Charging

In long persistent phosphors,energy is stored in the traps by illuminating the phosphor with high-energy light.This characteristic of high-energy illumination has limited the development of long persistent phosphors in some fields（such as biological imaging optical probes）.In recent years,in order to expand the application of long persistent phosphors,many studies are being carried out.Based on the up-conversion charging（UCC）design,we demonstrate a“write”/“read”approach of traps upon illumination by a blue light-emitting diode（LED）in LaMgGa₁₁O₁₉:Cr³⁺,which offers an interesting technical advantage and an apparent convenience for applications.The specific experimental study is as follows:（1）Based on the UCC design and the luminescence kinetic rate equation,a novel“write”/“read”technology on optical information storage of persistent phosphors is designed.LaMgGa₁₁O₁₉:Cr³⁺was irradiated with blue LED to manipulate the trap.Our investigation indicates that the phosphor can be charged upon a high-power illumination(e.g.,incident power density,0.5 W·cm^-2)but discharged upon a low-power illumination(e.g.,0.1 W·cm^-2).And an appealing feature of the present approach is that the charging and discharging share the same illumination wavelength.（2）We devise experiments to characterize the trap depth and up-conversion charging mechanism of LaMgGa₁₁O₁₉:Cr³⁺.After illuminating the LaMgGa₁₁O₁₉:Cr³⁺with a blue LED(0.5 W·cm^-2),the thermoluminescence curve was measured at 100 h delay,and the curve was fitted using the initial heating method.The experimental results show that the phosphor has strong energy storage capacity and the trap depth is1.1 eV.To further study the UCC design of LaMgGa₁₁O₁₉:Cr³⁺,the phosphor was illuminated by blue lasers,green lasers and red lasers separately.A series of thermoluminescence curves were tested to prove that the UCC of the phosphor is the up-conversion of excited state absorption.