Up- and down-conversion emissions from Er3+ doped K2YF5 and K2YbF5 crystals

Crystals of Er3+ doped K2YF5 and K2YbF5 as well as stoichiometric K2ErF5 have been grown under hydrothermal conditions. Peculiarities of Er3+ luminescence in these crystals have been studied under different excitation wavelengths and, in particular, it has been discovered that in 5 at% Er3+:K2YbF5, the energy transfer (ET) efficiency from Yb3+ to Er3+ reaches 67%. Under near-IR excitation at 980 nm, this crystal is characterized by intense yellow up-conversion luminescence with CIE coordinates: x=0.449, y=0.465. Under UV and visible excitation at 355 and 532 nm, respectively, clear evidences of the down-conversion process through the cross-relaxation have been found. The corresponding efficiency of ET from Er3+ to Yb3+ is 69%. These features make Er3+:K2YbF5 crystals attractive for developing luminescent up- and down-converters for enhancing the performance of solar cells.