Investigation of upconversion luminescence for Tb³⁺/Yb³⁺ co-doped CaLnAlO₄ (Ln = Y, Gd, La) phosphors

Tb³⁺/Yb³⁺ co-doped CaGdAlO₄ phosphors were synthesized by a conventional solid-state reaction method. Green UC emission was obtained from the prepared samples under 980 nm excitation via a cooperative energy transfer process. The cooperative energy transfer efficiency from Yb³⁺ to Tb³⁺ and the phonon-assisted energy transfer efficiency from Tb³⁺ to Yb³⁺ were evaluated to be ~40% and ~1%, respectively. Partial substitution of Gd³⁺ ions with Y³⁺ or La³⁺ ions leads to an increase of UC intensity due to the enhancement of local distortion. The results indicate that the synthesized phosphors may be used to increase the efficiency of perovskite-based photovoltaic cells excited by green light.