Chapter 2. Aspects of applied inorganic photochemistry: the photographic process

Radiation Effects and Defects in Solids

Baetzold

et al. 2002

Self Cite

The imaging efficiency of today's photographic film and paper is influenced in a variety of ways. Among them, the incorporation of dopants is widely used to increase efficiency, control contrast or improve imaging deficiencies such as reciprocity law failure. Transition metal-organic ligand dopants are attractive because the organic ligand influences the photographic properties. Experimental studies have shown that many of these dopants incorporate well into the silver halide microcrystal even with large organic ligands. In this paper, experimental and computational results are presented on a variety of Ir-OL dopants in AgCl where OL is a small nitrogen and=or sulfur-containing heterocycle. Electron paramagnetic resonance methods provide information about the electronic structure, electron trapping properties and the stability of the electron trap state. These results are complemented by ab initio studies that give information about the optimum structure, charge compensation and the possibility of electron and hole trapping.

Section: Photo-epr=endormentioning

confidence: 98%

“…Polyvalent transition-metal (TM) ions are frequently used as dopants to limit reciprocity effects, control contrast, and reduce recombination inefficiencies [1][2][3]. These dopants interact with photogenerated electrons and holes.…”

Section: Introductionmentioning

confidence: 99%

Defects in the silver halide photographic process

Pawlik

Radiation Effects and Defects in Solids

Baetzold

et al. 2002

Self Cite

“…SET dopants are typically used at about 10-IOOppm so that the intensity of the shallowly trapped electron signal can be 1000 times greater than that observed for intrinsic shallow traps [3]. EPR can be used to monitor the concentration of electrons in shallow traps (11) as a function of temperature and exposure.…”

Section: Shallow Electron Trapping At Intrinsic and Extrinsic Sites Amentioning

confidence: 99%

“…Formally, it has a charge of +e/2 and a density of about 10'5-10'6~m-2 on a typical octahedral AgBr grain with an edge length of 0.5 pm [3]. From the results of pulsed-laser microwave photoconductivity (MWPC) experiments performed at 34.9 GHz [5], shallow trapping of the electron at the kink site occurs in less than 0.1 ns at room temperature.…”

Section: The Photographic Processmentioning

confidence: 99%

Defects and the photographic process

Olm

Radiation Effects and Defects in Solids

1999

The high imaging efficiency of today's color negative film depends on the unique defect properties of silver halides. We have chosen two important defect topics to highlight: defect-induced anisotropic crystal growth, and shallow electron trapping at surface defects and transition metal dopant sites. High imaging efficiency depends on the ability to concentrate photoelectrons and thereby to form a single latent image center per crystallite. This requires electron localization at a partially-charged, shallow electron trap at the surface followed by a shallow-deep transition to a metastable atom state. Subsequent ionic and electronic trapping processes that build the latent image occur only at this site. In some cascs, doping the bulk of the microcrystal with extrinsic shallow electron traps can improve latent image formation efficiency. Electron concentration does not occur at these dopant sites since they are not partially charged. Magnetic resonance and photoconductivity studies of the dynamics of shallow trapping by dopants and of the shallowdeep transition at surface sites are presented.

“…A combination of cyclotron resonance [1,2], electron paramagnetic resonance (EPR) [3], electron-nuclear double-resonance (ENDOR) [4], and optically detected magnetic resonance (ODMR) techniques [5,6] have been used to follow the progress of electron processes from photo-generation to the formation of the latent image. EMR spectra obtained from free carriers near the conduction band edge [1,2], electrons localized at intrinsic and impurity centres that function as shallow traps [1,2,[7][8][9], and electrons deeply trapped at impurities [3,[10][11][12] and sensitizers [13], have all contributed to our understanding of the photographic process. In contrast, information on the behaviour of photo-holes in these materials is less complete.…”

Section: Introductionmentioning

confidence: 99%

Multifrequency electron paramagnetic resonance and electron-nuclear double-resonance studies of photo-hole processes in AgBr and AgCl emulsion grains

J. Phys.: Condens. Matter

Pawlik

Baetzold

2000

By using a combination of multifrequency EPR spectroscopy, ENDOR spectroscopy and calculations of structure and energy, the reactivities of photo-generated holes in microcrystalline AgBr and AgCl dispersions (photographic emulsions) have been followed in detail. Progress has been facilitated by the use of both gelatin and polyvinyl alcohol (PVA) as peptizers. The initial trapped hole centres produced by band-gap excitation have been identified. In AgBr, this species is [(Br 4 ) 3− •V], a neutral complex formed from hole trapping by the four nearest neighbours of a surface Ag + vacancy (=V). [(Br 4 ) 3− •V] reacts with gelatin to produce a transient organic radical at the grain's surface. It does not, however, react with PVA. The formation of the oxidized gelatin radical might involve atomic bromine as an intermediate. In AgCl, the well-known self-trapped hole centre (AgCl 6 ) 4− is the initial hole species. The hole diffuses by an electron exchange process until it is trapped by a silver ion on the grain's surface or within its penultimate layer of lattice ions. It is subsequently released from this Ag 2+ site to be retrapped at a centre containing four equivalent Cl − ions. The precise identity of this defect has yet to be determined, but its decay also results in the oxidation of gelatin.