Multi-color luminescence properties and energy transfer behaviour in host-sensitized CaWO4:Tb3+,Eu3+ phosphors

Abstract

A series of host-sensitized and color-tunable CaWO₄:Tb³⁺,Eu³⁺ phosphors were prepared via a high-temperature solid-state reaction route, and the crystal structure and luminescence properties, especially the energy transfer behavior, were investigated in detail. Under UV radiation, the CaWO₄ host presents a broad emission band from about 320 to 600 nm centered around 415 nm, ascribed to the charge transfer in WO₄²⁻ groups; while Eu³⁺ and Tb³⁺ ion doped CaWO₄ samples show both host emission and respective emission lines derived from the characteristic f–f transitions of activators, which present abundant emission colors owing to an efficient energy transfer from the host to Eu³⁺/Tb³⁺ ions. The energy transfer from the host to Eu³⁺ and Tb³⁺ was evidenced by directly observing appreciable overlap between the excitation spectrum of the host and the emission spectrum of Eu³⁺/Tb³⁺, as well as by the decreased decay time of host emission with increasing Eu³⁺/Tb³⁺ concentration. The energy transfer mechanisms in CaWO₄:Eu³⁺/Tb³⁺ phosphors have been determined to be a resonant type via dipole–dipole interaction. In the Eu³⁺ and Tb³⁺ co-doped system, CaWO₄:Eu³⁺,Tb³⁺, the energy transfer phenomenon not only occurs from host to activators, but also from Tb³⁺ to Eu³⁺, resulting in color-tunable emission including white light by simply adjusting the doping concentration of Eu³⁺ and Tb³⁺ ions. The PL properties of the as-prepared materials indicate their promising application in solid-state lighting fields.