Infrared emission and defect centres in Er and Yb codoped Y3Al5O12 phosphors

YAG phosphor powders doped/codoped with Er3+/(Er3+ + Yb3+) have been synthesised by using the solution combustion method. The effect of direct pumping into the I-4(11/2) level under 980 nm excitation of doped/codoped Er3+/Yb3+-Er3+ in Y3Al5O12 (YAG) phosphor responsible for an infrared (IR) emission peaking at similar to 1.53 mu m corresponding to the I-4(13/2)-> I-4(15/2) transition has been studied. YAG exhibits three thermally-stimulated luminescence (TSL) peaks at around 140A degrees C, 210A degrees C and 445A degrees C. Electron spin resonance (ESR) studies were carried out to identify the centres responsible for the TSL peaks. The room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0176 is identified as O- ion, while centre II with an isotropic g-factor 2.0020 is assigned to an F+ centre (singly ionised oxygen vacancy). An additional defect centre is observed during thermal-annealing experiments and this centre (assigned to F+ centre) seems to originate from an F-centre (oxygen vacancy with two electrons) and these two centres appear to correlate with the observed high-temperature TSL peak in YAG phosphor.