Spectral investigation of R, Ce:YAG ( R: Pr3+, Eu3+, Gd3+) single crystals and their applications in white LEDs
Du Yonga), Shao Chong-Yuna), Dong Yong-Junb), Yang Qiu-Honga), Hua Weib)
       
Schematic energy level diagrams of Ce3+, Eu3+, Pr3+, and Gd3+ ions.