Judd-Ofelt analysis and luminescence characteristics of Eu3+ doped Nepheline (NaAlSiO4)-based glass ceramics for solid-state lighting applications

Abstract

The present work addresses on the optical and spectroscopic properties of glass ceramics containing a hexagonal NaAlSiO4 crystalline phase (Nepheline) and Eu3+ dopant, prepared by melt-quenching technique followed by subsequent heat treatment. The precipitation of NaAlSiO4 crystals in the glass system with increasing heating temperature was determined by XRD analysis. The existing vibrational bands such as BO3, BO4, SiO2 and O-H groups in the glass network and the increase in the amount of non-bridging oxygens with increasing heating temperature of the precursor glasses were evaluated through FTIR spectroscopy. Morphological changes in the glass surface induced with the growth of NaAlSiO4 crystals is recorded by field emission scanning electron microscopy at resolutions of 1 µm and 200 nm. The impact of heating temperature and Eu3+ ions embedded in the NaAlSiO4 crystalline phase on the optical properties was studied using absorption spectra, excitation, emission spectra, and decay curves. The glass ceramics exhibited a decrease in their bandgap energy values and an increase in their Urbach energy values with heat treatment at higher temperatures. The Judd-Ofelt (J-O) intensity parameters evaluated from the emission spectra showed the trend Ω2>Ω4. The emission bands with intense electric dipole transition 5D0→7F2, long decay lifetimes, and improved quantum efficiency of Eu3+ ions evidenced the partitioning of Eu3+ ions into the NaAlSiO4 crystalline phase. Radiative calculations from the emission spectra showed a higher stimulated emission cross-section for glass ceramics. The CIE-1931 color coordinates, correlated color temperature (CCT, K), and color purity measurements favoured red emission from Eu3+ ions with better quality. Therefore, the prepared glass ceramics can favour the need for LED applications and laser devices.