Enhanced spectroscopic properties of holmium doped phosphate glass: Role of Ag/TiO2 nanoparticles embedment

Metal nanoparticles sensitized rare earth ions-doped inorganic oxide glasses with improved optical character-istics and optimum compositions became demanding for practical applications. However, the basic under-standing of the interaction mechanism between various rare earth ions and metallic nanoparticles remains deficient. Based on this fact, some holmium ions (Ho3+)-doped magnesium zinc sulfophosphate glasses with Ag/ TiO2 nanoparticles (NPs) co-activation were prepared using the melt-quenching process and characterized. Effects of Ag/TiO2 NPs co-activation at various contents on the physical, optical and structural properties of the glasses were determined. XRD analyses of the as-quenched samples confirmed their amorphous nature. FTIR and Raman spectra of the glasses showed structural modifications due to NPs incorporation. HRTEM image verified the existence of spherical Ag and non-spherical TiO2 NPs (mean size of 13.01 nm) in the glass matrix. The absorption spectra of the glasses displayed eleven significant peaks and photoluminescence spectra revealed prominent green (5F4 -> 5I8) and red (5F5 -> 5I8) emission peaks corresponding to various transitions in Ho3+. The oscillator strengths, Judd-Ofelt intensity and radiative parameters of the glasses were calculated to support the experimental results. The optical properties of the glasses were shown to improve via the Ag/TiO2 NPs co-activation. Among the prepared samples, glass containing 0.3 mol% of TiO2 NPs showed high stimulated emission cross-section (3.24 x 10-20 cm2) for the green emission, maximum quantum efficiency and radiative lifetime. The explanation of PL intensity enhancement and quenching mechanisms of Ho3+ may provide better understanding on the co-activation of metal/semiconductor NPs in the studied glasses.