Влияние связующего и красителей на механизм туннельной люминесепнции микрокристаллов AgBr(I)

Abstract

It was previously found that in emulsion microcrystals (EMC) AgBr (I) (with silver content corresponding to pBr 4), the centers responsible for tunneling recombination at T = 77 K, with a maximum of luminescence at λmax~ 560 nm when excited from light from the absorption region of AgBr (I) EMCs (λ ~ 450 nm) as a result of temperature quenching, they undergo structural transformation into centers, which, under the same excitation, provide tunneling recombination with a wavelength depending on the binder: for EMC AgBr (I) obtained in water ‒ λmax~ 720 nm, in gelatin ‒ λmax~ 750 nm. In the present work, similar structural transformations of the centers determining tunneling recombination with λmax~ 560 nm, to the centers with luminescence on λmax~ 720 nm were implemented for AgBr (I) EMCs synthesized in polyvinyl alcohol (PVA) with an increase in the content of silver ions in the emulsion (from pBr 4 to 7). Responsible for this transformation, as follows from the obtained results, are mobile interstitial silver ions Agi +, which transform these tunnel recombination centers. The effect of the binder on the recombination processes in EMC AgBr (I) is manifested in changes in the kinetics of the increase in luminescence with λmax~ 560 nm upon excitation by light from the absorption region of AgBr (I) EMC (λ ~ 450 nm) to a stationary level. For a binder whose molecules do not interact with Ag centers Agin+, n = 1, 2 (water, PVA at pBr 4), increase in luminescence with λmax~ 560 nm occurs monotonically from zero to the maximum stationary level. For a binder (in our case, G is gelatin), whose molecules with centers Agin+ (n = 1,2) form complexes (Agin0G+), the kinetics of the increase in luminescence in EMC AgBr (I) to a stationary level at λmax~ 560 nm at pBr 4 is characterized by the presence of “flash flare”. Adsorption on the surface of EMC AgBr (I) (in PVA at pBr 7) of the dye is manifested as follows: if, before the introduction of the dye, the kinetics of the increase in luminescence with λmax~ 560 nm, when excited from light from the absorption region of AgBr (I) EMC (λ ~ 450 nm) to a stationary level, “flare-up” appeared, then after the introduction of the dye, the luminescence increases with λmax~ 560 nm occurs monotonically from zero to the maximum stationary level. Studies of the “flash” of luminescence stimulated by infrared (IR) light, after the termination of the action of exciting light, showed that when the kinetics of the increase in luminescence with λmax~ 560 nm to the stationary level, it exhibits "flare-up", a "flash" stimulated by IR light is not observed at λ ~ 560 nm. In the absence of “flash flare”, a “flash” at λ ~ 560 nm is observed. From our point of view, the results obtained indicate that “flare-up burning” is due to the presence of deep centers of electron localization with a small capture cross section, and not a photochemical reaction stimulated by exciting light. Key words: AgBr (I) microcrystals, emulsions, glow centers, luminescence flare-up.