Improvement of spectroscopic properties and luminescence of Er3+ ions in phospho-tellurite glass ceramics by formation of ErPO4 nanocrystals

Er3+ doped phospho-tellurite glass was prepared by melt-quenching method. A limited partial crystallization of the glass samples was controlled by thermal annealing process in order to obtain a transparent glass-ceramic. The X-ray diffraction (XRD) patterns indicate the precipitation of nanocrystalline phases after heat treatment. A particular interest is devoted to the formation of ErPO4 nanoparticles (NPs) dispersed in the glassy host. The optical band gap (E-g) has been found to decrease from 3.37 to 2.75eV as the sample changes from glass to glass-ceramic. The Judd-Ofelt (JO) phenomenological intensity parameters (Omega 2, Omega 4, Omega 6) have been estimated by means of the absorption spectrum. Radiative parameters of Er3+ ions have been predictedusing JO intensity parameters. Significant improvements of both the near infrared emission relative to the I-4(13/2) -> I-4(15/2) transition and the corresponding luminescence lifetime were obtained after heat treatment. We show that an efficient excitation transfer occurs from the formed ErPO4 NPs to Er3+ ions. The Mc-Cumber method is used to calculate the absorption cross-section sigma(a), the emission cross-section sigma(e) and the gain cross-section G(lambda) relative to the I-4(13/2) -> I-4(15/2) transition. Compared with other glass hosts, the results indicate that erbium doped phospho-tellurite glass-ceramic has good prospect as a gain medium applied for 1.53 mu m band broad and high-gain erbium-doped fiber amplifiers (EDFA).