Li-doping effect on enhancement of photoluminescence in Gd2O3:Eu3+ films

Luminous properties of Gd2O3:Eu3+ and Li-doped Gd2O3:Eu3+ thin films were investigated by time resolved laser spectroscopy in the temperature range of 12–295 K. The films were grown by pulsed laser deposition method on Al2O3(0 0 0 1) substrates under different substrate temperature and oxygen pressures. Both cubic and monoclinic crystalline structures were observed in Gd2O3:Eu3+ films, but only the cubic crystalline structure was observed for Li-doped Gd2O3:Eu3+ films grown under certain conditions. The enhanced photoluminescence brightness by Li-doping results from the improved crystallinity and reduced internal reflections caused by rougher surfaces. Comparing to Gd2O3:Eu3+ films, the brightness of Li-doped Gd2O3:Eu3+ films was increased by a factor of 1.5 and 2.3 at 12, and 295 K, respectively. In this paper, it is suggested that the highest optical phonon energy of Li2O introduced Li to Gd2O3:Eu3+ is another important factor for the improved luminescence brightness at high temperature. Exciting the Gd2O3:Eu3+ films at its band gap or higher energy level of Eu3+ ions with 266 nm excitation results in cascading multi-phonon relaxation to the emitting state of Eu3+ ions (5D0), then luminescence of Eu3+ ions takes place. The optical phonon having the highest energy plays an important role in multi-phonon relaxation process. The photoluminescence intensity was increased with increasing temperature under 266 nm excitation.