Cost effective red emitting Eu3+ doped natural sodium feldspar (NaAlSi3O8) powder and photophysical changes on transition to glassy state

Abstract

There is a need for low cost red emitting materials for commercial phosphor converted white light emitting diodes (pc-WLEDs) due to low color rendering index (CRI) and high correlated color temperature (CCT) of currently existing InGaN pumped YAG:Ce3+ white LED. The present study involves the synthesis, characterisation and photoluminescence studies of Eu doped albite (NaAlSi3O8: x%Eu3+, x = 0, 0.5, 1, 2, 5). Successful doping of Eu3+ at Na+ site was observed to result in a small expansion of the unit cell. Under 395 nm excitation the phosphors show intense red band at 614 nm due to the trivalent europium ions. There is an enhancement in their red emission as well as internal quantum efficiency from 67 to 73 % with increase in the europium concentration. The luminescence decay lifetime of NaAlSi3O8: x%Eu3+ phosphor is having biexponential decay with short life time in microseconds and long lifetime in milliseconds endowed by their different proximity to sodium vacancies. The powdered sample was also converted to its glassy form by heating at 1200 °C to compare their photophysical properties. High asymmetry ratio and improved PL emission intensity of europium ion was found in the albite glass compared to crystalline powder whereas luminescence lifetime reduces. The CIE chromaticity diagram indicates the high color purity of the synthesized material. The present work demonstrated that the synthesized Eu3+ doped Albite powder and glass as a potential low-cost red emitting phosphor for the UV excitation.

Keywords

• Photoluminescence
• Eu3+ doped silicates
• Albite
• Red emitting phosphor
• Glass phosphors