Investigation of the up-conversion processes in Er3+:LiYF4 crystals 12

In this work, we investigated the up-conversion processes in LiYF4 (YLF) crystals doped with 1 mol% of Er3+ and containing 50 mol% of Er3+. The up-conversion processes include the excited state absorption (ESA) of pumping radiation process and the energy-transfer up-conversion (ETU) process. The luminescence lifetime was measured from decay curve of the 4S3/2 T 4I15/2 (556 nanometers [nm]) transition using pulsed laser excitations tuned between 967 and 999 nm from an optical parametric oscillator pumped by the second harmonic of a Q-switched Nd:YAG laser. We also studied the dipole-dipole and dipole-quadrupole interactions that occur among Er3+ ions in Er (50 mol%):YLF crystal. For this investigation, we used the Inokuti-Hirayama model that is due to an energy transfer between ions without involving the excitation migration through donors.