Abstract:In this work we present, for the first time to our knowledge, laser emission under wavelength selective laser-pulsed pumping in Nd 3+ -doped TeO 2 -ZnO-ZnF 2 bulk glass for two different Nd 3+ concentrations. The fluorescence properties of Nd 3+ ions in this matrix which include, JuddOfelt calculation, stimulated emission cross-section of the laser transition and lifetimes are also presented. The site-selective emission and excitation spectra along the 4 I 9/2 → 4 F 3/2 absorption band show the inhomogeneous behaviour of the crystal field felt by Nd 3+ ions in this fluorotellurite glass which allows for spectral tuning of the laser output pulse as a function of the pumping wavelength. The emission cross-section obtained from the Judd-Ofelt analysis and spectral data (4.9x10 −20 cm 2 ) is in fairly good agreement with the value obtained from the analysis of the laser threshold data (4x10 −20 cm 2 ).

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Transparent glass-ceramics containing Er 3+ -doped sodium lutetium fluoride nanocrystals for photonic applications have been synthesized. Glass transition temperature, softening temperature, and crystallization temperature were estimated by dilatometry and differential thermal analysis. Proper heat treatments were selected to crystallize lutetium fluoride nanocrystals. X-ray diffraction analysis was carried out to identify the crystalline phase and the crystal size. HRTEM indicates that the base glass is phase separated in droplets enriched in Lu, Na, F, and also Er ions. The thermal treatment induces the crystallization *mpascual@icv.csic.es inside the droplets. The optical characterization, which includes absorption and steady-state and time-resolved emission spectroscopy under one-and two-photon excitation, shows the differences between the phase-separated base glass and its corresponding glass-ceramic. The reduction of the Judd-Ofelt parameter Ω 2 together with the increase of the fluorescence lifetimes as compared to the glass sample confirms the presence of Er 3+ ions in a crystalline environment in the glass-ceramic samples. Moreover, an enhancement of the green and red up-converted emissions (as well as the weak blue emission) is observed in the glass-ceramic, indicating the Er 3+ incorporation into the nanocrystals. The possible excitation mechanisms responsible for this up-conversion luminescence are discussed on the basis of lifetime measurement results.

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Transparent oxyfluoride tellurite thin film glasses have been produced at room temperature by pulsed laser deposition in O 2 atmosphere from an Er-doped TeO 2 -ZnOZnF 2 bulk glass. Thin film glasses present high refractive index (n≥ 1.95) and good transparency (T≥ 80%) in the visible (λ> 400nm) and near infrared range. However, their photoluminescence (PL) performance at 1.5 µm is poor. Thermal annealing at moderate temperatures (T≤ 315 ºC), well below glass crystallization, increases the PL 2 intensity by more than one order of magnitude as well as the PL lifetime up to τ≈ 3.3 ms. Film glasses present a larger fraction of TeO 3 trigonal pyramids than the bulk glass and a very large OH -content. The structure and composition of film glasses does not change upon annealing and thus the activation of the PL response is related to the improvement of the surface morphology and the significant decrease of their OHcontent.

a b s t r a c tNanostructured thin film glasses with a controlled concentration and in-depth distribution of Er 3+ have been produced by alternate pulsed laser deposition (PLD) from host (PbO-Nb 2 O 5 -GeO 2 ) and dopant (Er) targets (in-situ doping). Their photoluminescence (PL) response is compared to that of doped films grown by standard PLD using Er 3+ -doped glass targets (ex-situ doping), by studying the characteristic Er 3+ emission at 1.53 lm. PL intensity of in-situ doped films is maximized for in-depth separation between Erdoped layers P5 nm, whereas their lifetime is always longer in the case of nanostructured films having a separation between Er 3+ ions similar to that of ex-situ doped films. These results stem from the different distribution of Er 3+ ions in the host glass: isotropic 3D for ex-situ doped films or planar 2D for nanostructured films. Thus, the number of neighbor Er 3+ ions is larger in the first case, which favors the increase of nonradiative deexcitation due to concentration quenching.