Color-tunable upconversion luminescence and prolonged Eu3+ fluorescence lifetime in fluoride KCdF3:Yb3+,Mn2+,Eu3+via controllable and efficient energy transfer

Due to the lack of intermediate levels and the large energy mismatch with Yb3+, the achievement of efficient upconversion (UC) of Eu3+ is a great challenge. Herein, intense UC emission of Eu3+ is demonstrated via controllable and efficient unidirectional energy transfer from Yb3+–Mn2+ dimers in perovskite fluoride KCdF3:Yb3+,Mn2+,Eu3+ synthesized by a facile solvothermal method. The UC emission color of KCdF3:Yb3+,Mn2+,Eu3+ can be well tuned from yellow to orange and ultimately turned into Eu3+ pure red emission by controlling the Eu3+ concentration. Moreover, a significantly prolonged Eu3+ UC emission lifetime is observed in this system, and it is ascribed to the genetic effect of the sustained resonance energy transfer from Yb3+–Mn2+ dimers to Eu3+. The pump power and temperature dependent UC behaviors further suggest that the phosphor exhibits excellent chromaticity stability. Owing to the long-lived and chromaticity stable UC luminescence, the as-prepared KCdF3:Yb3+,Mn2+,Eu3+ phosphor may be a highly suitable candidate for lifetime-encoded information encryption, anti-counterfeiting, etc.