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The absorption and luminescence spectra of Er3+-doped Ba2NaNb5O15 single crystals have been measured at 10 and 298 K. The lifetimes of the lower lying excited states, emitting in the visible and NIR regions, have been measured as a function of the temperature. From the oscillator strengths of the absorption transitions, the Judd-Ofelt intensity parameters have been evaluated. The spontaneous transition probabilities, the branching ratios and the radiative lifetimes have been determined for the most important emitting states using the calculated intensity parameters and the results have been compared with the experimental data. The stimulated emission cross section have been estimated for the 1.5 mu m transition. These experimental results are discussed in order to evaluate the potentialities of this material as active medium in solid state laser devices. (c) 2005 Elsevier B.V. All rights reserved.

We have measured the absorption, the visible emission spectra and the lifetimes of Ca3Sc2Ge3O12 single crystals activated with Ce3+ or Pr3+. The crystals were grown by the ‘flux growth’ method. The optical spectra of the Ce3+-doped crystal consist of broadbands as a consequence of the strong electron–phonon coupling in the 2D(5d1) excited level, the emission band being located in the blue-green region with maximum at about 480 nm. The spectroscopic properties of CaSGG:Pr are affected by inhomogeneous broadening arising from the presence of non-equivalent optical centres. The spontaneous transition probabilities, the branching ratios and the radiative lifetimes have been calculated in the framework of the Judd–Ofelt Theory and compared with the experimental results for the 3P0 and 1D2 levels. The emission cross-sections of the transitions originating from the 3P0 level were calculated and compared with those reported for other Pr3+-doped crystals of technological interest.

The paper presents the spectroscopic investigation of Pr 3+ ,Yb 3+ :BaY 2 F 8 and the characteristics of the upconverted emission from the 3 P 0 level due to an avalanche mechanism under infrared excitation around 820 and 870 nm. Absorption and emission measurements at 12 K were performed in order to refine the Stark level scheme. Room temperature absorption, emission, excitation spectra, and excited state absorption measurements were performed and analysed in order to investigate the properties of the avalanche mechanism and to determine the spectroscopic parameters of this system. Based on the determined spectroscopic parameters a system of differential equations was established in order to describe the observed avalanche mechanism.