Optical properties of titania nanoparticles embedded Er3+-doped tellurite glass: Judd-Ofelt analysis

Abstract

Judd–Ofelt (J–O) theory was used to analyze the optical properties of erbium (Er3+) ions doped zinc-sodium-tellurite glass system incorporated with titania (TiO2) nanoparticles (TNPs) for the realization of up-converted solid state lasers. Such glass systems were synthesized using melt quenching method to determine the influence of varying TNPs contents on the absorption and emission properties. J-O intensity parameters (Ω2, Ω4, Ω6), spectroscopic quality factor (χ = Ω4/Ω6), radiative transition probabilities, branching ratio, and radiative lifetime of various transitions involved in the Er3+ ions were calculated from the measured optical spectra. XRD pattern verified the amorphous nature of the prepared glass samples. TEM images manifested the growth of TNPs inside the glass matrix having mean size between 15 and 25 nm. UV–Vis–NIR spectra exhibited ten absorption bands centred at 407, 444, 452, 489, 522, 552, 653, 800, 976 and 1532 nm. Two surface plasmon resonance (SPR) bands of TNPs were evidenced at 552 nm and 580 nm. Luminescence spectra revealed three prominent peaks centred at 525, 545 and 660 nm, where the glass sample containing 0.2 mol% of TNPs displayed optimum intensity enhancement by a factor of 30.00, 28.57 and 19.60, respectively. This enhancement is primarily attributed to the TNPs surface plasmon enabled colossal localized electric field in the proximity of Er3+ ions and subsequent energy transfer to the Er3+ ions. Values of Ω2, Ω4, Ω6 and χ were ranged between (2.14−3.72)×10−20, (1.27−2.77)×10−20, (1.42−2.22)×10−20 cm2 and (0.58–1.94), respectively. Occurrence of higher values of Ω2 and Ω6 indicated the existence of lower symmetry and stronger covalency around the Er3+ ions. Furthermore, the decrease of χ values with increasing TNPs up to 0.2 mol% approved intensified lasing transition. Achieved higher values of Ω4 and Ω6 demonstrated that the present glass composition is a prospective lasing media.