Structure and transformations of tunnel-luminescence centres in emulsion microcrystals AgBr(I)

It is known that the tunnel luminescence in emulsion microcrystals (EMCs) of AgBr(I) at the temperatures T >= 77 K is determined by donor-acceptor complexes with a specific structure. Such a complex includes a paired iodine centre, which combines two neighbouring sites of anionic sublattice, and an interstitial silver ion Ag+ located nearby. If the AgBr(I) EMCs are distributed in a binder of which molecules do not interact with Ag+ ions, the centres are characterized by a luminescence band with the characteristic wavelength lambda(max) approximate to 560 nm. Modifications of the content of silver ions in the emulsion produce an additional luminescence band with lambda(max) approximate to 720 nm. If the AgBr(I) EMCs are distributed in gelatine, its molecules interact with clusters of silver ions and form specific complexes with the characteristic luminescence bands located at lambda(max) approximate to 580 nm and lambda(max) approximate to 750 nm. In both cases, two sorts of luminescence-glow kinetics can be observed, depending on the temperature and the Ag+ concentration: a monotonic intensity increase from zero to a maximum stationary level or a rapid `flash enhancement' followed by a gradual decrease to a lower value. Remarkably, the additional luminescence `flash' stimulated by infrared radiation is detected whenever the monotonic growth is observed. On the contrary, no infrared-stimulated glow occurs in the luminescence band when the `flash enhancement' is detected in this band. All of these results are interpreted in terms of structural transformations taking place with the tunnelrecombination centres in the AgBr(I) EMCs.