Temperature and doping dependence of fluorescence lifetime in Yb:YLF (role of impurities)

Abstract

We have investigated temperature and doping dependence of fluorescence lifetime in Yb:YLF crystals in the 78–300 K range, for samples with Yb-doping levels of 0.5%, 1% and 25%. Radiation-trapping prolonged fluorescence lifetimes are first measured to understand the pros and cons of this inevitable process on fractional thermal load and laser gain. Later, pinhole method was used to acquire ideally trapping free fluoresce lifetimes. For the lowly Yb-doped samples, fluorescence lifetime was measured to be 1.97 ms and 2.1 ms at 78 K and 300 K, respectively. For the 25% Yb-doped sample, strong upconversion emission due to the presence of Er, Tm and Ho impurities were observed. A double-exponential decay behavior, combined with excitation intensity dependent decay profile was also revealed for this highly doped sample. Even with the pinhole method, the 300 K fluorescence lifetime was measured as 4.5 ms, showing the difficulty to acquire radiation-trapping free signals at high doping levels. Time dynamics of upconverted emission in different spectral regions were also recorded, which provides hints on the energy transfer mechanisms between the Yb ion and the other rare-earth impurities. • Temperature and doping dependence of fluorescence lifetime is investigated in Yb:YLF. • Radiation-trapping extends effective fluorescence lifetime. • Increased doping and crystal temperature boost up radiation-trapping effect. • Amplified spontaneous emission and upconversion influence fluorescence decay curves.