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

Abstract Spectroscopic properties of the Tm3+ (4f12, 3H6) ions in Tm-doped and Tm–Ag co-doped glasses with Li2B4O7 (or Li2O–2B2O3) basic composition are studied. All investigated glasses show intense blue, red, and infrared emission bands of the Tm3+ ions. Experimental and theoretical oscillator strengths (fexp and fcal), Judd–Ofelt intensity parameters (Ω2, Ω4, Ω6) and radiative properties such as probabilities of radiative transition (Arad), branching ratios (β), radiative lifetimes (τrad), and quantum efficiencies (η) of the Tm3+ luminescence in the Li2B4O7:Tm and Li2B4O7:Tm,Ag were calculated. Presence of the Ag0 (4d105s1, 2S1/2) and Ag2+ (4d9, 2D5/2) paramagnetic centres and their aggregates in the Li2B4O7:Tm,Ag glass was confirmed by electron paramagnetic resonance. Luminescence spectra and decay kinetics of the Ag+ (4d10, 1S0) ions and small non-plasmonic Ag aggregates were registered and discussed. Increasing of quantum efficiency and yield of the Tm3+ luminescence in the Li2B4O7:Tm,Ag glass is explained by energy transfer from Ag species to the Tm3+ ions.