Investigation of a novel color tunable long afterglow phosphor KGaGeO4:Bi3+: luminescence properties and mechanism

Abstract

Although a variety of Bi³⁺-activated common luminescent materials have been investigated, few Bi³⁺-doped long afterglow phosphors have been discovered up to now. In this work, we developed a novel long afterglow material KGaGeO₄:Bi³⁺ by solid-state reaction. The highlight of this work is the observation of bright cyan to blue color tunable long afterglow of KGaGeO₄:Bi³⁺. The structural information of the samples was studied in detail using Rietveld refinement. Photoluminescence and phosphorescence properties of the phosphor were investigated systematically. The reason why the photoluminescence and phosphorescence color can be tuned has been discussed. A bright long afterglow could be observed by the naked eye for 3 hours in the dark after ultraviolet irradiation was ceased. Moreover, we have analyzed the reason why the KGaGeO₄ host is suitable for Bi³⁺ to generate afterglow emission by exploring the nature of traps in KGaGeO₄:Bi³⁺ with the help of thermoluminescence spectra. In this phosphor, Bi³⁺ ions doped in K⁺ sites behave as luminescence centers, while negatively charged defects serve as hole-trapping centers. In view of the experimental results, a feasible afterglow mechanism of KGaGeO₄:Bi³⁺ was also proposed and discussed.