Luminescence and defect centres in Tb 3+ doped LaMgAl 11O 19 phosphors

Abstract

Terbium (Tb) doped LaMgAl 11O 19 phosphors have been prepared by the combustion of corresponding metal nitrates (oxidizer) and urea (fuel) at furnace temperature as low as 500 °C. Combustion synthesized powder phosphor was characterized by X-ray diffraction and field emission scanning electron microscopy techniques. LaMgAl 11O 19 doped with trivalent terbium ions emit weakly in blue and orange light region and strongly in green light region when excited by the ultraviolet light of 261 nm. 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 thermally stimulated luminescence (TSL) process. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least two defect centres. One of the centres (centre I) with principal g-values g ∥ = 2.0417 and g ⊥ = 2.0041 is identified as O 2 − ion while centre II with an axially symmetric g-tensor with principal values g ∥= 1.9698 and g ⊥ = 1.9653 is assigned to an F + centre (singly ionized 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). The F centre and also the F + centre appear to correlate with the observed high temperature TSL peak in LaMgAl 11O 19:Tb phosphor.