Influence of Binder and Dyes on the Mechanism of Tunnel Luminescence of AgBr(I) Microcrystals

Abstract

It has been previously found that, in the AgBr(I) emulsion microcrystals (with a silver content corresponding to pBr 4), the centers responsible for tunnel recombination at T = 77 K with a luminescence maximum at λmax ≈ 560 nm when excited by light from the absorption region of the AgBr(I) emulsion microcrystal (λ ≈ 450 nm) as a result of temperature “quenching” are subject to structural transformation into the centers that, under the same excitation, provide the tunnel recombination with a wavelength depending on a binder: λmax ≈ 720 nm for the AgBr(I) emulsion microcrystals obtained in water and λmax ≈ 750 nm for those obtained in gelatin. In this work, similar structural transformations of the centers that determine the tunnel recombination at λmax ≈ 560 nm to the centers with a glow at λmax ≈ 720 nm are implemented for the AgBr(I) emulsion microcrystals synthesized in polyvinyl alcohol at an increase in the content of silver ions in the emulsion from pBr 4 to pBr 7. The mobile interstitial silver ions Ag $$_{i}^{ + }$$ are responsible for this transformation, as follows from the results obtained. The effect of the binder on the recombination processes in the AgBr(I) emulsion microcrystals is manifested in changes in the kinetics of the increase in luminescence from λmax ≈ 560 nm when light is excited from the absorption region of the AgBr(I) emulsion microcrystal (λ ≈ 450 nm) to a stationary level. The increase in luminescence at λmax ≈ 560 nm occurs monotonously from zero to the maximum stationary level at the binder whose molecules do not interact with the centers Ag $$_{{in}}^{ + }$$ , n = 1, 2 (water, polyvinyl alcohol at pBr 4). The kinetics of the increase in luminescence in the AgBr (I) emulsion microcrystals to a stationary level at λ ≈ 560 nm and pBr 4 is characterized by the presence of “flash enhancement” at a binder (in our case, gelatin (G)) whose molecules form the (Ag $$_{{in}}^{0}$$ G+) complexes with the Ag $$_{{in}}^{ + }$$ (n = 1, 2) centers. The adsorption on the AgBr(I) emulsion microcrystal (polyvinyl alcohol) surface of the dye is manifested as follows: if the kinetics of increase in luminescence at λmax ≈ 560 nm when excited by light from the region of the AgBr(I) emulsion microcrystal absorption (λ ≈ 450 nm) to the stationary level demonstrates “flash enhancement” prior to the introduction of dye, then, after the introduction of dye, the increase in luminescence at λmax ≈ 560 nm occurs monotonically from zero to a maximum fixed level. Studies of the “flash” of the luminescence stimulated by infrared (IR) radiation have shown that, after the termination of the exciting light when the kinetics of the increase in luminescence from λmax ≈ 560 nm to a stationary level demonstrates “flash enhancement”, the “flash” stimulated by IR radiation is not observed at λ ≈ 560 nm. In the absence of “flash enhancement”, a “flash” at λ ≈ 560 nm is observed. The results obtained, from our point of view, indicate that “flash enhancement” is due to the presence of deep centers of the localization of the electrons with a small capture cross-section and not to a photochemical reaction stimulated by the exciting light.