Influence of CaO and Dy2O3 on the structural, chemical and optical properties of thermally stable luminescent silicate nanoglass-ceramics

Abstract

In this work, nano-glass ceramics constituted by SiO2–Na2O–CaO–Dy2O3 are synthesized with different contents of CaO (0–30 mol%) and Dy2O3 (0.1–4 mol%) through the melt-quenching technique at 1500 °C. The precipitation of nanocrystals occurs during the cooling stage of molten glass precursors. Depending on CaO content, nanocrystals of cristobalite (0 mol%) or combeite (30 mol%) are grown inside the amorphous silicate phase. FTIR and XPS studies indicate that non-bridging oxygens increase with CaO due to [SiO]4 tetrahedral rupture. However, if CaO is higher than 20 mol%, the non-bridging oxygens slightly decrease due to the prevalence of combeite nanocrystals. Moreover, the addition of CaO decreases the optical bandgap (4.18–3.91 eV) and increases the Urbach energy (0.54–0.75 eV). Although PL spectra acquired at λex of 348 and 386 nm show four peaks whose intensities augment with CaO, the most prominent peaks appear at 490 (4F9/2 → 6H15/2, blue) and 577 nm (4F9/2 → 6H13/2, yellow). The decrease in the yellow to blue ratio, with an increment in CaO content, is attributed to the devitrification of glass phase. The most intense PL intensity is obtained in the nano-glass ceramic constituted of 30 mol% CaO and 1 mol% Dy2O3. This sample demonstrates excellent thermal PL stability up to 400 °C, retaining 95.2% of the initial PL value. The results indicate that these nano-glass ceramics are good candidates for their use as yellow phosphors in high-power consuming and high-temperature applications, such as LED chips and luminescent solar concentrators.

Keywords

• Silicate
• Nanoglass-ceramic
• Dy2O3
• Luminescence
• Thermal stability