Photochemistry of colloidal semiconductors 30. Reactions and fluorescence of AgI and AgI — Ag₂S colloids

Abstract

When Ag+ ions are precipitated with I− ions in the presence of poly (N‐vinyl pyrrolidone) or poly (vinyl alcohol) the AgI colloid forms slowly (during minutes or hours, depending on conditions), the changes in the absorption spectrum indicate the presence of unusual AgI structures during the first stages of particle growth. Size quantization effects are partly responsible for these changes. — AgI colloids with 10% excess of I− do not photolyse under continuous illumination. However, intermediates can be detected in flash photolysis experiments. In the presence of sulfite, silver is formed, the quantum yield lying in the 10−4 range. Greater yields of silver (10−3 to 10−2) are observed with solutions containing excess Ag+ ions. Less silver is produced in acidic solutions and the silver signal in the flash experiments decays more rapidly. These effects are attributed to the re‐oxidation of small silver clusters formed on the colloidal particles by H+ ions. — AgI colloids have a weak fluorescence close to the threshold of absorption. It is blue‐shifted with decreasing particle size (size quantization effect). The fluorescence is quenched by small amounts of silver deposited on the particles. It is also quenched by an Ag2S deposit. Under these circumstances a new fluorescence having three maxima in the red and infrared appears. This new fluorescence is red‐shifted with increasing size of the silver deposit (size quantization of Ag2S). The fluorescence is explained in terms of electron transfer from AgI (conduction band) to the hole captured at the AgI—Ag2S interface. Size quantization effects are also believed to play a role in the sulfursensitization of photographic plates.

Photophysics and charge dynamics of Q-PbS based mixed ZnS/PbS and PbS/ZnS semiconductor nanoparticles

“…Over the past one-and-a-half decades a variety of colloidal particles of metal sulfides and metal oxides have been prepared and investigated for their changed electronic properties. In the recent past several quantized nanoheterostructures of semiconductors, viz., CdS-Ag 2 S [8,9], CdS-TiO 2 [10][11][12][13], CdS-ZnO [10], CdS-PbS [14], AgIAg 2 S [15], CdS-HgS [16], CdS-ZnS [17], SnO 2 -CdS [18], ZnO-ZnS [19], etc., have been synthesized and characterized. A number of promising applications of these materials in photophysics, photocatalysis, and photonics have been reported.…”

Multiple-overtone resonance Raman scattering and fluorescence from I2 species adsorbed on silver surfaces

“…The fluorescence can be attributed to exciton recombination from silver iodide small clusters. 33,34 It was recently shown that oxidation of the iodide-modified silver surface resulted in the formation of small Ag clusters and, consequently, in an emission around 430 nm. 35…”

Effect of pH on Optic and Structural Characterization of Chemical Deposited AgI Thin Films

“…The crystallite size and crystal structure of AgI have been affected by growth mechanism which is important in terms of photosensitivity. Therefore, we have to give much attention to characterization and preparation of AgI [8][9][10][11][12][13][14][15][16] . According to the literature, it has been observed several polymorphic forms depending on the experimental conditions and the temperature of formation 17 .…”