2.85 µm fluorescence of Ho-doped water-free fluorotellurite glasses

Holmium doped fluorotellurite glasses with composition of xHo2O3 (wt%)+60TeO2–30ZnF2–10NaF (mol%) (xHo-TZNF60, x=0.50–1.50) were synthesized by physical and chemical dehydration technique (PCDH) and characterized as candidates of fiber laser glasses. Intense 2.85 µm fluorescence (Ho3+: 5I6→5I7) was observed experimentally when excited at 1163 nm. It is attributed to low phonon energy of fluoride component and water-free characteristic (αOH=0.027 cm−1). Ho-TZNF glass possess a large simulated emission cross-section of 1.51×10−20 cm2, a long fluorescence lifetime of ∼0.81 ms (1/e time of the initial part of non-exponential decay curve) and a broad transparent window of 2.1–4.2 µm. Among all the compositions of glass samples, 1.00Ho-TZNF60 is the optimized one, and thus is proposed to be the most potential material for 3.0 µm fiber laser. -- Highlights: • Fluorotellurite glass is a new mid-IR material combining the advantages of oxides and fluorides. • Ho-TZNF60 glasses can stimulate 2.85 μm emission longer than that of Er-doped ones. • Physical and chemical dehydration method is effective to remove OH groups from bulk mid-IR glasses. • Mid-IR fluorescence and direct lifetime of Ho ions were firstly reported in oxide-host glasses. • In contrast, 1.00Ho-TZNF60 glass is an ideal material to develop 3 um fiber lasers