Thermo-mechanical studies on Er3+-doped fluorophosphate glasses for near infrared lasers

Thermal, mechanical and thermo-mechanical properties of Mg(PO3)2-BaF2-CaF2-ErF3 fluorophosphate (FP) glasses with varying Mg(PO3)2 and ErF3 molar ratios have been investigated. The simultaneous thermal analysis revealed that the Tg, Tx, Tp and ΔT increased constantly with increasing Mg(PO3)2 and ErF3 content and that favorable large values of ΔT (>100 °C) were obtained at higher Mg(PO3)2 and ErF3 content. The thermo-mechanical analysis showed that the Tg and Ts increased constantly and coefficient of thermal expansion decreased from 16.5×10−6 K−1 to 11.2×10−6 K−1 with an increase in Mg(PO3)2 and ErF3 content. The Knoop hardness (HK) increased constantly from 381 kgf/mm2 to 480 kgf/mm2 with increased Mg(PO3)2 and ErF3 content, which indicates strengthening of the glass network with increased -PO bonds. The HK measurement at different applied loads and indentation times was carried out and from this study, it was found that an appropriate incorporation of cations into the FP glasses and the optimum rare earth concentration could considerably increase the thermal and mechanical strength of the glass. The studied glass compositions showed beneficial thermal properties and outstanding mechanical strength and can be applied for fiber drawing.