Thermoluminescent properties of Eu2+ and RE3+ co-doped phosphors CaGa2S4:Eu2+, RE3+ (RE=Ln, excluding Pm, Eu and Lu)

The thermo-luminescence (TL) of rare earth ions RE³⁺ (RE=Ln, excluding Pm, Eu and Lu) co-doped phosphors CaGa₂S₄:Eu²⁺, RE³⁺ was studied between room temperature and 300 °C, and 3D thermo-luminescence of the phosphors were measured from room temperature to 400 °C. The basic material CaGa₂S₄:Eu²⁺, showed at least two bands in the TL glow curve. Changing the auxiliary activator RE³⁺ (rare earth ion), intensities and the positions of the TL glow curve peaks were affected significantly. For the phosphors with long afterglow, auxiliary activator such as Ce³⁺, Pr³⁺, Gd³⁺, Tb³⁺, Ho³⁺, or Y³⁺ created some new defects in these compounds at lower trap levels and enhanced their TL intensities. The Nd³⁺ or Er³⁺ auxiliary activator only enhanced TL intensities to a low extent, so these two phosphors have short persistent luminescence at room temperature. TL intensities of La³⁺, Sm³⁺, Tm³⁺ or Yb³⁺ co-doped phosphors were suppressed greatly and no afterglow was shown. The relationship between auxiliary activators and corresponding thermo-luminescence curves of phosphors CaGa₂S₄:Eu²⁺, RE³⁺ are discussed in detail. According to our results, suitable activation energy and enough high corresponding trap density are necessary for the phosphor with long afterglow.