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

Highlights: • Phosphate-tellurite glasses doped with Er³⁺ are prepared using the melt quenching method. • Nanocrystalline phases are formed in the glassy host after thermal treatment of the glasses at T = T_g. • Improvement of optical parameters of Er³⁺ are seen after the formation of ErPO₄ nanoparticles. -- Abstract: 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 (Ω2, Ω4, Ω6) 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 ⁴I_13/2 → ⁴I_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 σ_a, the emission cross-section σ_e and the gain cross-section G(λ) relative to the ⁴I_13/2 → ⁴I_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 μm band broad and high-gain erbium-doped fiber amplifiers (EDFA).