Fading of TL and OSL Signal

The Blue band at 480 nm is also related to oxygen impurities in AlN. Thus, in [46] it was assumed that the Blue band occurs due to recombination process with participation in role of acceptor of (v [-20j.j) center comprised of two close oxygen ions substituting for nitride ion and an aluminum vacancy. The 

Application of Jain s model is restricted to materials where D and A form spatially correlated donor-acceptor pairs (DAPs) with randomly distributed separation distance between components in DAPs. At least two experimental facts, mentioned above, indicate that AIN ceramics belongs to such materials  

In the diagram, both defect centers responsible for the UV emission band - 0].j and Oj.j-Va - are presented with ground and excited states forming energy levels between the valence and conduction bands. Irradiation with 245 nm (5.06 eV), corresponding to excitation of the UV band in PL, causes excitation and ionization of Oj.j-v centers. Released electrons move through the conduction band until capture in 0].j and other electron traps. Also direct electron transition onto without involvement of the conduction band is possible. As a result, Oj.j-v centers become acceptors, and Oj., centers - donors, close DAPs with different separation distances are formed. Tunnel transition from the excited state of D to the ground state of A is followed with emission of UV luminescence. 

The tunneling probability depends on separation distance between D and A - the larger separation distance, the lower recombination probability, and longer lifetime of survived A and D. The closest DAPs recombine already during irradiation, providing PL. The more distant pairs deplete successively during 

AGL according to increase of separation distance. At the same time, energy of recombination emission decreases with rise of separation distance. That is why the red shift of UV emission band is observed with delay time in the AGL emission spectrum (see Equation 9.1). 

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