Photoluminescence, thermoluminescence and electron spin resonance studies on Eu3+ doped Ca3Al2O6 red phosphors

Abstract

Tricalcium aluminate doped with Eu3+ was prepared at furnace temperatures as low as 500°C by using the convenient combustion route and examined using powder X-ray diffraction, scanning electron microscope and photoluminescence techniques. A room-temperature photoluminescence study showed that the phosphors can be efficiently excited by UV/Visible region, emitting a red light with a peak wavelength of 616 nm corresponding to the 5D0–7F2 transition of Eu3+ ions. The phosphor exhibits three thermoluminescence (TL) peaks at 195°C, 325°C and 390°C. Electron Spin Resonance (ESR) studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the defect centres responsible for the TL process. Room-temperature ESR spectrum of irradiated phosphor appears to be a superposition of three distinct centres. One of the centres (centre I) with principal g-value 2.0130 is identified as O− ion while centre II with an axially symmetric principal values g ∥=2.0030 and g ⊥=2.0072 is assigned to an F+ centre (singly ionized oxygen vacancy). O− ion (hole centre) correlates with the TL peak at 195°C and the F+ centre (electron centre), which acts as a recombination centre, is also correlated to the 195°C TL peak. F+ centre further appears to be related to the high temperature peak at 390°C. Centre III is also assigned to an F+ centre and seems to be the recombination centre for the TL peak at 325°C.