Spectroscopic and luminescent properties of the lithium tetraborate glass co-doped with Nd and Ag

Abstract

Spectroscopic and luminescent properties of the Nd-doped and Nd–Ag co-doped borate glasses with Li2B4O7 (Li2O–2B2O3) basic composition are investigated and analysed using optical absorption, electron paramagnetic resonance (EPR), photoluminescence (excitation, emission, decay kinetics) experimental methods and Judd–Ofelt analysis. Optical absorption, photoluminescence spectra and decay kinetics of Nd3+ ions were registered and detailed analysed. Experimental and theoretical oscillator strengths (fexp and ftheor), Judd–Ofelt intensity parameters (Ω2, Ω4, Ω6), and important to laser applications radiative parameters such as probabilities of radiative transitions (Arad), branching ratios of luminescence (β), radiative lifetimes (τrad), emission cross-sections (σem), and quantum efficiency (η) of the Nd3+ luminescence in the Li2B4O7:Nd and Li2B4O7:Nd,Ag glasses have been calculated. Broad absorption band of surface plasmon resonance (SPR) related to silver nanoparticles was observed in the Li2B4O7:Nd,Ag glass. Presence of the Ag paramagnetic centres and aggregates in the Li2B4O7:Nd,Ag glass was confirmed by EPR spectroscopy. Photoluminescence emission and excitation spectra as well as decay kinetics of the Ag+ ions and small non-plasmonic Ag aggregates or nanoclusters were registered and discussed. Observed enhancement of the Nd3+ luminescence intensity in the Li2B4O7:Nd,Ag glass is explained by effects induced by SPR of the Ag nanoparticles as wells energy transfer from Ag+ ions and Ag aggregates to the Nd3+ ions.