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

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 V ''' V-Ga,V-''''(Ge) and V '(K) defects serve as holetrapping centers. In view of the experimental results, a feasible afterglow mechanism of KGaGeO4: Bi3+ was also proposed and discussed.