Temperature and time dependent photoluminescence of single crystalline KEu(WO4)2

This work describes the growth of crack-free single crystals of KEu(WO4)2 and their characterization with respect to spectroscopic properties. The crystal structure of KEu(WO4)2 was refined from single crystal X-ray diffractometer data at 293 (KY(WO4)2 type, C2/c, a = 1069.88(7), b = 1046.87(5), c = 760.47(5) pm, β = 130.774(4)°, wR2 = 0.0513, 1247 F2 values and 57 variables) and 90 K (a = 1067.69(4), b = 1048.45(4), c = 757.87(3) pm, β = 130.784(2)°, wR2 = 0.1078, 1237 F2 values and 57 variables). It turns out that KEu(WO4)2 is a promising material for some demanding application areas due to its excellent thermal stability. Temperature dependent spectroscopy revealed that the thermal quenching temperature T1/2 of the crystalline material is 699 K (426 °C). From time dependent emission spectra the fluorescence lifetime τr was determined to be 498 ± 2 μs at 3 K. The decay time moderately declines down to 480 μs at room temperature pointing to the presence of very little thermal quenching at ambient conditions. A strong decline of the emission integral and decay time is not observed before reaching almost 600 K. Finally, the quantum efficiency was determined to be about 64% at room temperature and the asymmetry ratio for the 5D0 -7F2 to 5D0 -7F1 emission multiplets is about 10.8, which means that the Eu3+ spectrum is dominated by the 5D0 – 7F2 transition. 151Eu Mossbauer spectroscopic and temperature dependent magnetic susceptibility data confirm stable trivalent europium.