The generation and decay of photoelectrons is an important factor in improving photographic efficiency of silver halide
crystals. Microwave absorption phase-sensitive detection technology designed by our experiment group, was used to
non-contact measure the transmission characteristic of photoelectronic in [Fe(CN)6]4- uniformly-doped AgCl
microcrystals. The signal of free and shallow-trapped photoelectrons were measured in-phase. It is found that the
photoelectrons decay time in cubic AgCl microcrystals doped with [Fe(CN)6]4- is longer than that of undoped samples at
the first exposure time. And the photoelectrons decay time becomes longer with the doping concentration increasing. As
is shown the doping centres can act as shallow electron traps. The results also show the photoelectrons decay time
decreases significantly till becoming a constant after a few minutes exposure, and the constant is lower when the doping
concentration is higher. By analysis the photoproduct is silver clusters with the characteristic of deep electron traps in the
microcrystals. The measurement of photoelectrons by microwave absorption phase-sensitive detection technology can
give evidence for the improving performance of the photosensitive material, optical information storage material and so
on.
The decay curve of free photoelectron in cubic AgCl microcrystals by sulfur sensitization is obtained by microwave absorption dielectric spectrum detection technique. By comparing the free photoelectron decay curves of unsensitized and sensitized sample, we discover that sulfur sensitization centers act as shallow electron trap when sensitization time is 45min. In order to analyze the characteristics of sulfur sensitization center quantitatively, the method of the decay kinetics of photoelectron is used in this paper. We first proposed a model of sulfur-sensitized AgCl microcrystals, and then induced a series of kinetics equation. The characteristics curve of photoelectron decay is obtained by solving the kinetics equation, which is in agreement with the experimental curve. Meanwhile the concentration, trap depth and capture cross-section are obtained by computer simulation, which are 1.12ppm, 0.085eV and 1.46×10-18cm, respectively. Also a possible method to study the mechanism of sulfur sensitization from the perspective of dynamics is suggested.
Using femtosecond time-resolved upconversion fluorescence spectroscopy technology, the fluorescence decay properti-es of J-aggregates of anionic-cationic cyanine dye, anionic cyanine dye and cationic cyanine dye adsorbed on surfaces of the cubic AgBrI grains are investigated. The kinetics of the electron transfer and the spectral sensitization property are analyzed in detail. The experiment setup in our work is the fluorescence upconversion(also called fluorescence frequen-cy generation)spectrometer. The time-resolution reaches about 140 fs. Anionic-cationic cyanine dye studied in our ex-periment is new-type cyanine dye, which formed by anionic cyanine dye reacting with cationic cyanine dye.
By contrary of the sensitization performances of several cyanine dyes, It is found that the sensitization performance of cubic AgBrI sensitized by anionic-cationic dye is marked higher than those of anionic cyanine dye, cationic cyanine dye and the mixture of anionic cyanine dye and cationic cyanine dye. The fluorescence decay curves of cyanine dyes J-aggregates obtained by femtosecond fluorescence upconversion spectrometer are analyzed as a sum of double exponent-ials, and the fitting curves consist of a fast and a slow component. Because of the large amplitude, this fast decay should be mainly attributable to the electron transfer from dye J-aggregates to conduction band of AgBrI. The electron transfer velocity of anionic-cationic cyanine dye J-aggregates is larger than those of anionic cyanine dye, cationic cyanine dye and the mixture of anionic cyanine dye and cationic cyanine dye, which is consistent with the results of the sensitization performance and the photoelectron lifetime. Dye1 has higher sensitizing efficiency than other cyanine dyes on the cubic AgBrI grains.
In this experiment the microwave absorption and phase-sensitive detection technique was used to detect the time-resolved signal of photoelectrons generated by 35-ps laser pulses in AgCl emulsions uniformly doped with different concentrations of formate ions (HCO2-). According to photoelectron decay signal, the photoelectron decay properties and the trap-capture properties, influencing the efficiency of latent image formation of the cubic AgCl grains, were discussed. The results indicate that when its concentration is 10-5mol/molAg, the formate ions act as hole traps obviously, enhancing the escape of electrons from pair recombination, but when its concentration is more than or less than 10-5mol/molAg, the formate ions may not act as hole traps effectively. We find that the optimal concentration of uniformly doped formate ions which can increase the photoelectron lifetime effectively is 10-5mol/molAg.
Direct detection of the dynamics of photo-induced electrons in AgBr photographic system sensitized by dye-55026 was performed using picosecond time-resolved fluorescence spectroscopy. The dependence of the electron transfer rate on different conditions and microcosmic mechanism of electron transfer were analyzed. The experiment setup in our work was a system of high-speed streak photography (Streak Cameras) with a time-resolution of 5 ps. With stead spectroscopy, the peak of absorption and fluorescence of J-aggregation on AgBr grains both have a red shift contrast to monomer. On the same time the absorption spectrum band of J-aggregation becomes narrow. The fluorescence decay curves of J-aggregation on both the cubic and tabular AgBr grains (T-grains) were gained with different dye concentrations. These curves are fitted well by a sum of double exponential functions, which includes a fast and a slow component. Because of large amplitudes (68-99% for T-grains and 68-80% for cubic grains) of the fast decay (2.4-12.1ps for T-grains and 4.1-5.8ps for cubic grains) and the estimated quantum yield of the electron injection, this fast decay should be mainly attributable to the electron transfer from excited J-aggregation to conduction band of AgBr. At low concentration (<4.51mmol/molAg), the fluorescence decay lifetime for T-grains is longer than that for cubic grains. As the increase of the concentration, it will become more rapidly for T-grains than that for cubic grains.
Photoelectron decay characteristics in latent image formation process directly reflect photographic efficiency of silver halide crystals. Dopants can be substitutionally incorporated into AgX crystals and influence the photoelectron action by introducing appropriate electron traps. Long photoelectron lifetime can improve the photographic efficiency of intrinsic or unsensitized grains. In general, AgCl are intrinsic or unsensitized emulsion. Cubic AgCl microcrystals doped with K4Ru(CN)6 were measured by microwave absorption and dielectric-spectrum technique. Measurement of the photoelectron decay process as a function of doping position and concentration can provide important information about the electronic properties. The experimental results show the photoelectron decay time at room temperature is more or less longer than undoped samples. The photoelectron decay time increases with the doping concentration increasing and with the doping position closer to the core except for position 30%Ag and over high concentration 3.21x10-5 mol/molAg. When doping position is 30%Ag, the photoelectron decay time reaches its maximum at the doping concentration of 1.5x10-5 mol/molAg. At doping concentration 3.21x10-5 mol/molAg, the photoelectron decay time reaches its maximum at the doping position 60%Ag. Through studying the photoelectron decay behavior, we can know the doping can improve the image quality of AgCl emulsion.
Photoelectrons play an important role during the photographic process of silver halide. Electron traps influence the decay of photoelectrons and the photographic process as well. During the preparation of silver halide microcrystal, traps will be formed with different depth, concentration, and capture cross section under different conditions such as temperature, pressure, and nucleation time etc. The electron trap with different depth, concentration and capture cross section has different ability to capture photoelectrons. In this paper, the influences of the three parameters on photoelectron decay are theoretically analyzed from the point of the photoelectron decay kinetics, respectively. It is found that decay amount is determined by capture cross section; decay velocity depends on trap depth; trap concentration influences both decay amount and velocity. Photo-storage or imaging character of silver halide material can be changed and improved by changing the size of capture cross section, depth or concentration under certain condition to control decay amount or velocity.
The action curves of free photoelectrons and shallow-trapped electrons in silver halide microcrystals are obtained by microwave absorption phase-sensitivity detection technique. Through comparing the relationship between electronic amounts and exciting intensity, the theory of Gurney-Mott optical absorption is verified. The electronic decay properties in different silver halide microcrystals are analyzed and the effects of electronic behavior on the sensitization properties in silver halide microcrystals are discussed.
Using a computer simulation, AgCl emulsions doped with [Fe(CN)6]4- complexes and a reference AgCl emulsion without dopants have been investigated at room temperature, and the free photoelectron decay time (FPT) was obtained. According to compare with the experimental results obtained by microwave absorption dielectric spectrum detection technology, the shallow electron traps (SETs) information was gotten. In this simulation, a model, which consists of a [Fe(CN)6]4- related SETs and intrinsic centers including two types of electron traps and a recombination center, is proposed. The model results in a set of differential equations that describe the kinetics of photographic generation, trapping, thermal detrapping and recombination processes. The FPT was simulated through solving these differential equations. Adjusting the simulation parameters of SETs to fit the experimental data, a number of important conclusions about SETs dopants were drawn from the simulation study.
Photo-electron decay characteristics in imaging process directly decide photographic efficiency of AgX emulsion. Microwave Absorption and Dielectric Spectrum Measure Technique (MADSMT) is a powerful tool to detect the change of emulsion film illuminated by light Through detecting the changes of reflect voltage in MADSMT, the decay signals of free electrons and shallow-trapped electrons will be obtained. In our work, the sulfur-sensitized silver halide material samples are used, which are made in different conditions, for example different temperatures and different densities. In order to record the whole decay process, a YAG laser system whose pulse width is 35ps is used as an exposure light. Finally the mechanism of sulfur-sensitized centers has been discussed and the influence of different conditions has been compared and analyzed.
Photoelectron plays an important role in latent image formation in silver halide materials, and its decay process is connected with the photographic process. Therefore, more details about the photoelectron decay behavior are needed in order to improve the photographic efficiency of imaging materials. In this paper, we use a single computer to simulate the photoelectron decay process in AgC1 microcrystals doped with [Fe(CN)6]4- that acts as shallow electron traps (SETs). First, we propose a model, which consists of a [Fe(CN)6]4- related SETs and intrinsic centers of pure AgC1 including two types of electron traps and a recombination center, where first a hole is trapped that then combines with a free photoelectron. The model results in a set of differential equations that describe the kinetics of generation, trapping, thermal detrapping and recombination processes. The decay process of the photoelectrons is simulated through solving these differential equations. In this simulation, the photoelectron decay curves, which fit well with experimental results, can be obtained quickly and accurately. With the aid of the simulation, the decay curves of the free photoelectron and the shallow-trapped electron are obtained accurately. A number of important conclusions about the SETs were drawn from the simulation study.
A YAG super short pulse laser (355nm, 35ps) is used as an exposure source. The free photoelectron lifetime and decay process of silver halide crystals could be measured and analyzed by the microwave dielectric spectrum detection equipment (MWA). This is a powerful tool that could quickly detect the change of dielectric function of AgX microcrystal. This technology enables measurement of the free photoelectron and shallow trapped electron decay process simultaneously that decide the sensitivity and other efficiency of silver halide material.
A YAG super short pulse laser (355nm, 35ps) is used as an exposure source. The electron action in imaging process is directly related to photographic efficiency of silver halide emulsion. Photoelectrons generated under actinic illumination of photographic silver halide systems occur in free, shallow-trapped and deep-trapped states. Different state of electrons has different influence on the dielectric function of silver halide material. The contributions of free and shallow-trapped electrons to the real and the imaginary part of the dielectric function are different by some orders of magnitude. The lifetime of different kinds of electrons can describe these complex processes and the lifetimes of free and shallow-trapped electrons can also reflect the sensitivity and other efficiency of silver halide emulsion. Microwave Absorption and Dielectric Spectrum Detection Technology is a powerful tool that could quickly detect the change of dielectric function of emulsion film. The lifetime and decay curve of the free photoelectrons and shallow trapped electrons of different emulsion samples have been measured and analyzed.
The optoelectron lifetimes in imaging process are directly related to photographic efficiency of silver halide emulsion. The lifetime of the free electrons and shallow trapped electrons decide the sensitivity and other efficiency of silver halide emulsion. Modern emulsion technology uses the incorporation of well-defined phase boundaries in emulsion crystals to reduce the recombination rate of optoelectrons and optoholes after actinic exposure. This process leads to an enhanced photographic efficiency due to the increasing optoelectron lifetime. Microwave absorption and dielectric spectrum detection technology is a powerful tool that could quickly detect the change of dielectric function of emulsion film. This technology enables contactless measurement of the optoelectron lifetime. YAG super-fast pulse laser (355 nm, 35 ps) is used as an exposure source. Signals of the free optoelectrons and shallow trapped electrons are the decay curve versus the time. The concentration of the optoelectrons depends on the maximum concentration and decay rate constant. The reciprocal of the slop of this straight line is the lifetime of the optoelectrons. The lifetime and decay curve of the free optoelectrons and shallow trapped electrons of different emulsion samples have been measured and analyzed.
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