A novel red-emitting phosphor with an unusual concentration quenching effect for near-UV-based WLEDs

Abstract

The luminescence of most phosphors activated with rare earth ions decreases when the doping amounts of activators exceed their critical concentrations, while some phosphors with special anisotropic structures have been found to have no concentration quenching effect. In this work, an unusual concentration quenching phenomenon being different from the two mentioned above was observed in GdGaTi₂O₇:xEu³⁺, that is, the luminescence intensity of the phosphors remains almost constant in the concentration range of x from 0.3 to 0.6, and it is obviously quenched when x is greater than 0.6. The reason for this phenomenon is deduced to be closely connected with the preferential distribution of quenching centres along the one-dimensional chains of rare earth ions in the host. The results of the first-principle calculations show that the confined chains for energy migration favour the formation of defects, and the formation energy of Gd vacancies in the chains increases with the concentration of Eu³⁺. This special chain structure accelerates the quenching of luminescence for phosphors with higher contents of Eu³⁺, thereby resulting in the unusual concentration-dependent luminescence in GdGaTi₂O₇:Eu³⁺. Moreover, the relatively balanced and excellent comprehensive performances of GdGaTi₂O₇:Eu³⁺, including high doping concentration, quantum efficiency of 71%, colour purity of 93.5%, colour rendering index of 91, and high thermal stability (the luminescence intensity at 400 K is 71% of that at room temperature), indicate a promising application prospect as a red component in WLEDs.