Tailoring the Glass Composition to Increase the Thermal Stability without Impacting the Crystallization Behavior of Oxyfluorophosphate Glass

Abstract

Even though the (75 NaPO3-25 CaF2) (in mol%) glass can be heat-treated into transparent glass-ceramic with Er3+ doped CaF2 crystals precipitating in the volume of the glass during heat-treatment, this glass was found to be a poor glass former, limiting its use as upconverter under 975 nm pumping. In this study, the impact of the glass composition on the thermal, optical and structural properties of the glass was investigated in order to understand how the glass composition can be tailored for the development of thermally stable upconverter glass-based material. The addition of MgO, Fe2O3 and Al2O3 in the NaPO3-CaF2 glass system increases the thermal stability of glass due to the depolymerization of the glass network. However, the changes in the glass composition also impacted on the nucleation and growth process. Indeed, CaF2 and other crystals were found in the newly developed glasses after heat-treatment leading to glass-ceramics with lower intensity of upconversion than the (75 NaPO3-25 CaF2) glass-ceramic used as a reference. Glasses were also prepared with different concentrations of Er2O3 and ErF3. These glasses were found to be promising as not only are they thermally stable, but they also exhibit green and red emission with high intensity under 975 nm pumping due to Er3+ clustering.

Near-infrared rechargeable glass-based composites for green persistent luminescence

“…The structure of the glass is investigated using IR spectroscopy. The IR spectra of the investigated glasses are similar to those reported in [25,26] (Fig. 2).…”

“…6a). The mean size of the crystallites is estimated using the Scherrer's equation as in [26] and is estimated to be 16 nm in the Yb1 glass-ceramics, similar to the one reported in Er 3+ doped glass in the same glass system [26,34]. The mean size of the crystallites increases slightly to ∼24 nm when the concentration of Yb 2 O 3 increases to 3 mol%.…”

“…6b). However, other crystals such as NaPO 3 (ICDD 04-011-3120) and Na 2 Ca 2 P 2 O 7 F 2 (ICDD 04-012-1844) are present in the Yb2 and Yb3 glasses when heat treated at (T g +20 °C) for 17 h and then at T p for 1 h. Similar crystals were reported to precipitate in Er 3+ doped glasses during heat treatment [25,26]. It is the presence of these additional crystals which is thought to reduce the transparency of the Yb2 and Yb3 glasses compared to the Yb1 glass after heat treatment (Fig.…”

“…Since an enhancement of the UC properties was reported after a thermal treatment of Er 3+ -doped glasses in similar glass systems due to the volume precipitation of Er 3+ -doped CaF 2 crystals occurring during heat treatment [25,26], the glasses were heat treated for 17 h at (T g +20 °C) and then at their respective T p for 1 h in order to check if a heat treatment of the investigated Yb 3+ , Tm 3+ co-doped glasses can also be applied to enhance their UC properties. After heat treatment, the glasses are translucent with no noticeable sign of surface crystallization in agreement with the loss in the transmittance of the glasses after heat treatment (see Fig.…”

“…6a). According to [25,26], the growth of the NaPO 3 and Na 2 Ca 2 P 2 O 7 F 2 crystals at the expense of CaF 2 crystal can be related to the high temperature used during the crystal growth step. Thus, when the crystal growth step is performed at 390 °C instead of the T p of each glass, only the peaks related to CaF 2 crystals can be seen in the XRD pattern of the heat treated Yb2 and Yb3 glasses (Fig.…”