Temperature-dependent luminescence and crystal-field levels of Eu3+ in orthorhombic KGdF4

Luminescent properties of Eu3+ ions in orthorhombic KGdF4 nanocrystals are investigated with high resolution emission spectra measured under the selective excitation of a tunable laser at the temperature of 20 K. Only the emission from one kind of site is detected, and the crystal-field levels of Eu3+ ions in this site, up to 5D2 multiplet, have been identified according to the recorded emission spectra. The symmetry of the site occupied by Eu3+ ions is discussed based on the numbers of emission lines of 5D0-7FJ transitions. A temperature-dependent luminescence is observed under the excitation of 5D2 at 465.5 nm. The emission from 5D1 is nearly absent at 20 K, while plays an important role in the emission spectrum at 300 K. This indicates that the direct relaxation from 5D2 to 5D0 dominates at low temperature. The different processes of the relaxation of 5D2 at 20 and 300 K are discussed with the measured decay curves of the emission from 5D0.