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

Highlights: • Growth of crack-free KEu(WO₄)₂ single crystals. • Time and temperature dependent spectroscopy between 3 and 800 K. • Scintillating properties of single crystalline KEu(WO₄)₂. • High thermal quenching temperature T_1/2 = 699 K. -- Abstract: 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 T_1/2 of the crystalline material is 699 K (426 °C). From time dependent emission spectra the fluorescence lifetime τ_r 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 Mössbauer spectroscopic and temperature dependent magnetic susceptibility data confirm stable trivalent europium.