Effect of silver nanoparticles on optical properties of erbium-doped magnesium phosphate glass

Three series of phosphate glass with composition (59.5-x)P2O5-40MgOxAgCl-0.5Er2O3 (0.0≤x≤1.5 mol%), (59.5-x)P2O5-40MgO-xAgCl-1.5Er2O3(0.0≤x≤1.5 mol%) and (69.7-x)P2O5-30MgO-0.3Er2O3-xAgCl, where x=0 or 0.5mol% were prepared using melt quenching technique. The amorphous nature of theglass was confirmed using the X-ray diffraction (XRD) method. The homogeneousdistribution of spherical Ag nanoparticles (NPs) (average size of 37 nm) in the glassymatrix was evidenced from the transmission electron microscopy (TEM) analyses.The UV-VIS-NIR absorption spectra showed 7 bands corresponding to 4I13/2, 4I11/2,4I9/2, 4F9/2, 4S3/2, 2H11/2, 4F7/2 transitions. The absorption spectrum of Er3+ ions freeglass sample containing Ag NPs displayed a prominent surface plasmon resonance(SPR) band located at ~528 nm. The infrared to visible frequency up-conversion(UC) emission under 797 nm excitation showed two emission bands of green (4S3/2-4I15/2) and red (4F9/2-4I15/2) corresponding to Er3+ transitions. An enhancement in UCemission intensity of both green and red bands was observed in the presence of silverNPs either by increasing annealing time or by NPs concentration. The enhancementof UC emission was understood in terms of the intensified local field effect due tosilver NPs. For first series of samples, the Judd-Ofelt parameters (Ω2, Ω4 and Ω6)were calculated and were found to lie in the range (8.05-9.20) ×10-20 cm2, (2.00-2.58)×10-20 cm2 and (1.05-2.30) ×10-20 cm2 respectively. These parameters were used toestimate the important parameters such as radiative transition probability (A),stimulated emission cross-section, radiative life time (τR) and branching ratio(βR) for the excited levels of Er3+ ions in the glass. Furthermore, the value of Ω2 forthe studied glasses was found to be higher than that of glasses reported in theliterature. These relatively higher values of Ω2 reflect low symmetry and highcovalency around the Er3+ ions. These phosphate glass nanocomposites can bepotentially used as photonic and plasmonic materials