Photoluminescence down-shifting studies of thermally stable Eu3+ ions doped borosilicate glasses for visible red photonic device applications

Abstract

In this paper we report the synthesis of thermally stable borosilicate glasses doped with europium ions having chemical composition 35B2O3.20SiO2.(15-x)Al2O3.15ZnO.15Na2CO3.xEu2O3 (x = 0.5 to 2.5 mol%) using melt quench process. A broad hump without any sharp peaks observed in the XRD spectrum recorded for an undoped glass confirm its glassy nature. The DSC & TGA has been conducted on an undoped glass to understand thermal stability and aggregate weight loss. Raman spectrum recorded for an undoped glass reveal various functional groups present in the host glass along with its phonon energy. The absorption spectral features recorded for the as prepared glasses are used to estimate optical band gap. In the process of understanding the effective usage of the as prepared glasses in visible red photonic device applications, the spectral features such as photoluminescence (PL) excitation, PL emission and PL decay were recorded and analyzed. Under 393 nm sharp excitation, all the glass samples are showing red emission corresponds to 5D0 → 7F2 transition (612 nm) and whose intensity continuously increasing with Eu3+ ion concentration up to 2.5 mol%. The red to orange color ratio (R/O) estimated from the recorded PL spectral features varies from 3.62 to 3.92 within the variation limits of Eu3+ions from 0.5 to 2.5 mol% indicates relatively low symmetry around Eu3+ ions in the as prepared glasses. Relatively higher R/O ratio also reveals that the nature of bonding between Eu3+ ions and the surrounding ligands as covalent. The Judd-Ofelt theory has been applied to the emission spectral features to understand the nature of bonding between the doped RE ion and its surrounding ligands along with the radiative properties of the doped RE ion. Activation energy (0.175 eV) and percentage loss (82%) in PL intensity estimated for 2.5 mol% of Eu3+ions through temperature dependent PL (TDPL) studies reveal the superiority in thermal stability of the as prepared glasses. The PL, TDPL, PL decay studies conducted along with CIE coordinates estimated allows us to contemplate that, the as prepared glasses are quite useful in fabricating thermally stable visible red photonic devices.