Spontaneous and stimulated UV luminescence of ZnO : N at 77 k

International audienceThe spontaneous and stimulated UV luminescence spectra of ZnO:N samples possessing different nitrogen contents are measured at a temperature of 77 K. Luminescence peaks resulting from bound and free excitons, biexcitons, and electron recombination via the nitrogen acceptor level are identified. The optical depth (123 meV) of the N-O impurity acceptor level is determined. It is established that stimulated UV luminescence originating from inelastic exciton interaction sets in as the optical pump power increases. (c) 2005 Pleiades Publishing, Inc

Energy transfer in Ce and Eu co-doped barium thiogallate: A photoluminescence characterization

In this work we report for the first time the fluorescence properties of Ce3+ single-doped and Ce3+/Eu2+ co-doped BaGa2S4 crystals, studied by means of time resolved measurements. The single-doped samples fluorescence was characterized by the Ce3+ radiative transitions from the 2D level to the 2F5/2 and 2F7/2 levels with a lifetime of 18 ns, and by a radiative transition from the Eg level to the ground state of Ce3+ ions with a lifetime of 11 ns. The co-doped samples fluorescence was characterized by Eu2+ radiative transition from 4f6d state to the ground state with a lifetime of 290 ns. Ce3+ emissions in co-doped samples are strongly quenched and a lifetime of 6 ns is observed. The reported data are discussed in the framework of energy transfer process between Ce and Eu. The rate of the energy transfer was estimated in 7.5 × 107 s-1 with efficiency of 66%

Low-temperature thermoluminescence in CaGa2S4 : Eu2+

In the last years many insulating and semiconducting materials activated with rare-earth elements were found to exhibit phosphorescence and thermoluminescence properties, and are attracting increasing interest due to the variety of application of long-lasting phosphors. In this work we studied the phosphorescence decay and thermoluminescence properties of CaGa2S4:Eu2+ as a function of temperature in the 9-325 K range. The comparison between spectra recorded as a function of time delay from the excitation pulse at different temperatures indicates that long-lasting emissions peaked at about 2.2eV occurs at Eu2+ sites. Thermoluminescence glow curve is characterized by five components at 69, 98, 145, 185 and 244 K. Experimental data are discussed in the framework of generalized order of kinetic model and allow to estimate the activation energies of trapping defects. The origin of glow components at 69, 98 145 and 244 K is correlated to trapping defects induced by Eu2+ doping, while the component at 185 K is attributed to a continuous distribution of defects. (c) 2008 Elsevier B.V. All rights reserved