Effect of thermal annealing procedure on the structure and photoluminescence of Er-doped fluorotellurite film glasses produced by Pulsed Laser Deposition

Abstract

Fluorotellurite glasses combine the good mechanical, thermal, and chemical properties of oxide glasses with the low phonon energy characteristic of fluoride crystals, which makes them attractive hosts for rare-earth (RE) ions. In addition, photoluminescence (PL) emission efficiency of RE-doped fluorotellurite glasses can be improved through the nucleation of a glass-ceramics phase, which provides the RE-ions with a local fluoride crystalline environment that is immersed in an oxide glass matrix. Yet, practical application of these materials for the development of all-optical networks requires good quality Er-doped thin films that allow the design and fabrication of robust, low-cost, miniature waveguide amplifiers (EDWAs) based on the 4I13/2-4I15/2 emission transition of Er3+ at 1.5 µm. In previous works, we have successfully produced transparent Er-doped TeO2-ZnO-ZnF2 thin film glasses by pulsed laser deposition at room temperature. Their structure is similar to that of the parent bulk glasses; however, they show a poor 1.5 µm PL response that has been related to a large OH- concentration, which makes annealing treatments necessary to activate their PL emission. In this work, we compare the efficiency of three different annealing approaches to improve PL emission of Er3+ ions: In-situ annealing during film growth, post-deposition annealing in air and post-deposition excimer pulsed-laser annealing. The effect of annealing parameters (temperature and time in the first two cases and laser energy density and number of laser pulses in the latter) on glass structure and PL intensity and lifetime at 1.5 µm is presented and discussed. Our results show that excimer laser annealing is preferable to conventional post-deposition annealing. However, the largest PL emission intensity and longest lifetime are achieved for films deposited on heated substrates. No signs of crystallization are observed in PL spectra; which suggest that PL enhancement is most likely related to a decrease of OH- concentration in the film glasses.