Photoluminescence emission in Er-activated good quality fluorotellurite thin film glasses

Summary form only given. New applications of optical communications technologies, such as high-density WDM schemes require functional integrated optical circuits allowing operation in the whole range of the telecommunication window (1.2-1.7 μm). However, Er-doped silica still constitutes the backbone of current technologies due to the characteristics of the <;sup>4<;/sup>I<;sub>13/2<;/sub>→<;sup>4<;/sup>I<;sub>15/2<;/sub> emission transition of Er<;sup>3+<;/sup> ions at 1.5 μm. Yet, this need has generated a large effort to find materials able to satisfy these requirements. Fluorotellurite glasses are particularly attractive for the development of integrated gain media since they combine the good optical properties of fluorides (a broad transparency range, low optical losses, and low phonon energies) with the better chemical and thermal stability of tellurite glasses. Moreover, they show high rare-earth (RE) ion solubility and present a variety of sites for the RE-ions, all of which broaden the photoluminescence (PL) bandwidth and enhance the radiative emission [1,2]. However, the production of good quality thin film RE-doped fluorotellurite glasses still constitutes a challenge [3].In our experiments we exploit the advantages of pulsed laser deposition (PLD) in the case materials having complex stoichiometry [4], to produce Er-doped fluorotellurite (TeO2-ZnO-ZnF2) thin film glasses. Transparent films were synthesized at room temperature in an oxygen pressure. Structural characterization of the deposited films shows a similar structure than the parent bulk glass, although they resulted enriched in oxygen and with a small reduction of fluorine content. Optical characterization shows that film glasses present large linear refractive index (nm 1.95 @ 1.53 μm) with reduced absorption (k <;0.01), while their transmission is similar to that of the parent bulk glass (Tm 80 % in the 0.5-2.0 μm range).Absorption and emission PL spectra and lifetimes have been measured in the visible and infrared regions. Figure 1.a compares the room temperature normalized PL spectra corresponding to the 4I13/2-4I15/2 transition of Er3+ ions measured for thin films annealed at 310 °C and for the parent bulk glass. As can be seen form the figure both spectra are similar although a slight decrease of the emission shoulders at 1.50 and 1.55 μm is observed in the case of the film glasses. It is also noticeable that thin film glasses show a large increase of the PL intensity at 1.53 μm upon annealing at temperatures close to 300 °C (Figure 1.b). The evolution of the PL intensity and lifetime upon annealing will be discussed in terms of the effect of annealing on the glass structure and the probability of nonradiative energy transfer between Er3+ ions.