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 degrees 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.