Abstract
Two series of NaY1-xTmxGeO4 olivines with x = 0.005–0.04 and x = 0.0–0.2 have been prepared by the solid state reaction method and citrate technique, respectively. These germanates crystallize in olivine structure and have the orthorhombic lattice, space group Pnma, Z = 4. The diffuse reflectance spectra have been measured and the optical band gap has been estimated. Under 808 nm laser diode excitation, the NaY1-xTmxGeO4 samples yield luminescence in the range of 1300–1600 nm (3H4 → 3F4) and 1600–2200 nm (3F4 → 3H6). The maximum of luminescence integrated intensity has been achieved for the composition NaY0·85Tm0.15GeO4. The luminescence decay kinetics has been explained using migration. The parameters of the cross–relaxation process: 3H4 + 3H6 → 3F4 + 3F4 were obtained taking into account the energy transfer rate between thulium ions. It is shown that the presented materials are characterized by an effective migration-accelerated cross-relaxation process, which occurs as a result of dipole-dipole interactions.
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