Elucidating photoluminescent properties of Eu-doped Ca-Al-Si-O(-N) glasses and the local structures of Eu ions

Europium (Eu) ion-doped luminescent materials have attracted considerable attention for their numerous optical applications. Eu-doped Ca-Al-Si-O(-N) glasses were synthesized from a mixture of oxynitride glasses and Eu2O3 powder using a standard melt-quenching technique in a radiofrequency furnace. The source Eu trivalent ions primarily changed to Eu2+ during melting, and the ratio of Eu2+ ions increased with an increase in Eu content in the starting mixture. All the prepared glasses exhibited photoluminescence (PL) owing to the 5d-4f transition of Eu2+ ions. The absorption edge and PL wavelength shifted to longer wavelength with an increase in Eu content. Moreover, oxynitride glasses exhibited a longer wavelength than those of oxide glasses. The internal quantum efficiency (IQE) increased with the increase in Eu content until it reached a maximum. X-ray absorption structure and electron spin resonance spectroscopies were used to determine the local structure of Eu ions, which confirmed that changes in the local structure of Eu ions were responsible for the shift in PL peak and the change in IQE. The development of the Eu-doped Ca-Al-Si-O-N glasses is highly inspiring for transparent phosphors.