Site-sensitive energy transfer modes in Ca3Al2O6: Ce3+/Tb3+/Mn2+ phosphors

Abstract

Ce³⁺/Eu²⁺, Tb³⁺ and Mn²⁺ co-doping in single-phase hosts is a common strategy to achieve white-light phosphors via energy transfer, which provides a high color rendering index (CRI) value and good color stability. However, not all hosts are suitable for white-light phosphors due to inefficient energy transfer. In this study, the site-sensitive energy transfer from different crystallographic sites of Ce³⁺ to Tb³⁺/Mn²⁺ in Ca₃Al₂O₆ has been investigated in detail. The energy transfer from purplish-blue Ce³⁺ to Tb³⁺ is an electric dipole–dipole mode, and the calculated critical distance (R_c) suggests the existence of purplish-blue Ce³⁺–Tb³⁺ clusters. No energy transfer is observed from purplish-blue Ce³⁺ to Mn²⁺. In co-doped phosphors based on greenish-blue Ce³⁺, however, the radiative mode dominates the energy transfer from Ce³⁺ to Tb³⁺, and an electric dipole–quadrupole interaction is responsible for the energy transfer from Ce³⁺ to Mn²⁺. A detailed discussion on the site-sensitive energy transfer modes might provide a new aspect to discuss and understand the possibilities and mechanisms of energy transfer, according to certain crystallographic sites in a complex host with different cation sites, as well as provide a possible approach in searching for single-phase white-light-emitting phosphors.