Analysis of optoelectronic properties and development of new persistent phosphor in Ce³⁺-doped garnet ceramics

抄録

Ce³⁺-doped garnet materials have attracted a great deal of attention in w-LEDs and scintillators applications because of their various optical properties. In 2011, we reported intense photocurrent by blue light excitation in Y₃Al_5−xGa_xO₁₂ (Yttrium Aluminum Gallium Garnet, YAGG):Ce³⁺ phosphors with high Ga content. With increasing Ga content in YAGG:Ce, the energy gap between the lowest excited 5d level (5d₁) and the conduction band (CB) decreases because the crystal filed splitting of Ce³⁺ becomes much smaller and the CB energy decreases. Based on the photoconductivity results, we concluded that Y₃Al₂Ga₃O₁₂:Ce³⁺ luminescence is quenched by thermal ionization. Utilizing the thermally assisted photoionization by blue light excitation, we tried to prepare a blue light chargeable persistent phosphor. In 2013, we found that Cr³⁺ ions act as suitable electron traps for persistent luminescence at room temperature in YAGG:Ce³⁺, and successfully developed the blue light chargeable persistent phosphors. In YAGG:Ce³⁺–Cr³⁺ persistent phosphors, the charging process (thermal ionization process) and detrapping process were controlled by CB energy engineering.