Orange-reddish photoluminescence enhancement and wollastonite nanocrystals formation induced by CaO in Sm3+-doped calcium sodium borosilicate glasses

The influence of CaO content on the structural, chemical, and optical properties of Sm3+-doped calcium sodium borosilicate glasses is presented. Different undoped and Sm3+-doped borosilicate glasses with varying CaO (0–30 mol%) and Sm2O3 (0–4 mol%) contents were synthesized using the melt-quenching technique at 1300–1400 °C. Although XRD results showed the amorphous nature of all the glasses, HRTEM analysis revealed the formation of small wollastonite nanocrystals with sizes in the range of 10–25 nm for 30 mol% of CaO. FTIR and XPS analyses indicated the occurrence of the boric anomaly in glasses with 0–10 mol% CaO contents, causing an increase in the [BO4]- units and a decrease in [BO3] units. The high-resolution O 1s and Si 2p XPS spectra, studied as a function of increased CaO content, revealed the continuous formation of non-bridging oxygens that increased the glass structure's asymmetry and promoted the formation of interstitials used as host for Sm3+ ions. Consequently, PL intensity of Sm3+-doped borosilicate glasses increased with the addition of CaO, reaching a maximum at 30 mol%. Besides, the optimization of Sm2O3 doping concentration produced the highest intensity at 0.25 mol% with orange-reddish emission (CIE coordinates: x = 0.60, y = 0.40). These glasses have potential applications as n-UV and blue-excited LED-driven orange-reddish phosphors in white solid-state lighting devices and color displays.