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.