Effect of silver co-doping on luminescence of the Pr3+-doped lithium tetraborate glass

Spectroscopic and luminescent properties of the Pr-doped and Pr-Ag co-doped borate glasses with Li2B4O7 (Li2O-2B(2)O(3)) composition are studied and discussed. Experimental and theoretical oscillator strengths (fexp and ftheor), phenomenological parameters (omega(2), omega(4), omega(6)), radiative properties (Arad, beta, trad), and quantum efficiencies (eta) of the Pr3+ luminescence were calculated basing on the obtained experimental results and Judd-Ofelt theory. Most intense band of the Pr3+ luminescence is peaked at 601 nm (D-1(2) -> H-3(4) transition). Presence of the isolated Ag+ (4d(10), S-1(0)) ions, small non-plasmonic Ag aggregates (Ag-m(n+) nanoclusters), and plasmonic Ag metallic nanoparticles in the Li2B4O7:Pr,Ag glass was proposed basing on analysis of the photoluminescence and optical absorption spectra. Observed enhancement of luminescence intensity and increasing of stimulated emission cross-section and quantum efficiency of luminescence in the Li2B4O7:Pr,Ag glass is explained by energy transfer from Ag species to the Pr3+ ions as wells local-field effect induced by Ag nanoparticles.