Effects of Gd/Lu ratio on the luminescence properties and garnet phase stability of Ce3+ activated GdxLu3-xAl5O12 single crystals

The luminescence properties of Ce3+ activated (Gd,Lu)3Al5O12 single crystals are investigated as a function of the Gd/Lu ratio with the aim of an improved understanding of the luminescence quenching, energy transfer processes, and garnet phase stability. Upon heavy substitution of Lu with Gd, the target garnet phase becomes thermodynamically unstable and unwanted secondary phase inclusions arise. The secondary phase shows luminescence properties in the UV spectral range. The thermal quenching process of the 5d→4f emission of Ce3+ in the garnet phase is determined by the temperature dependence of the photoluminescence decay time and delayed radiative recombination decays. The results show that the onset of the thermal quenching is moved to lower temperatures with increasing the Gd3+ content. The main mechanism responsible for the luminescence quenching is due to the non-radiative relaxation from 5d1 excited state to 4f ground state of Ce3+. The energy transfer processes between Gd3+ and Ce3+ as well as between secondary and garnet phase are evidenced by the photoluminescence excitation and emission spectra as well as decay kinetic measurements.