In the preparation of emulsion, the addition of certain dopants can significantly improve the photographic performance of the emulsion, such as improving sensitivity, increasing contrast, and improving the reciprocity rate of high illumination failure. Scholars at home and abroad have done more research on the application of dopants. For example, BHCarroll et al15 systematically studied the effect of iridium salt (Ir3 +) on the photographic performance of silver halide emulsions. They believe that iridium salt ions of different valence states and their ligands complex The effects of the substances in the emulsion are different. Their research shows that: (1) the sensitizing effect of iridium salt on the formation of latent image; (2) the sensitizing effect of iridium salt on the direct positive emulsion; (3) Reduce creases and scratches; (4) Stabilize and prevent fogging; (5) Other functions, such as improving contrast, improving high-illumination reciprocity failure, etc.
Platinum (Pt) etc.) naked ions and their ligand complexes. The main function of this type of dopant is to introduce extra net energy levels in the forbidden band of the band structure of the AgX crystal to capture photoelectrons and form electron traps, causing competition with the shallow shadow center for photoelectrons and improving the contrast (r). When the dopant enters the position of the AgX lattice, there are two types of electron traps formed: I71: (1) Deep electron trapping, the lifetime of the photoelectrons it captures is longer than the time of latent image formation or permanently captures photoelectrons, which is not conducive to the formation of latent images. Causes desensitization; (2) Shallow electron traps, the life of photoelectrons captured by it is shorter than the time of latent image formation or temporarily captures photoelectrons, which is conducive to the formation of latent images, which improves sensitivity and improves the reciprocity of high illuminance. The function is mainly the group VI1D + 2 valence metal hexacoordination complex, such as 4, 4'4-,) to study the effect of sensitivity.
2.1 Experimental scheme Taking the low-sensitivity pure bromine cubic emulsion model as the research object, the same amount of ruthenium salt () was added to different positions of the emulsion particles and the same position was added with different amounts of ruthenium salt dopant to conduct experiments respectively, comparing the sensitivity of each emulsion. Change, thus selecting the best conditions for ruthenium salt () as the dopant.
2.2 Emulsion synthesis experiment equipment: emulsification equipment, two mature equipment, pH acidity meter, silver electrode, reference electrode.
Experimental raw materials: AgN03, KBr, NH4N03, dilute H2S04, NaOH, deionized gelatin and water. Emulsion synthesis: A and B series pure bromine cube emulsions are synthesized at T = 42 ° C. The average particle size of the emulsion particles is d = 0.30.4um. Among them, A series uses nail salt () as the dopant.
2.3 Experimental results 2.3.1 Pure bromine cube A series emulsions are now added ruthenium salt () to the emulsion synthesis stages in the amount of 5.Xl6mol.1111 (11) /0101.Ag, and then the synthetic emulsion is subjected to secondary ripening and exposure (0.05 seconds), developed and processed with n-1 liquid, the photographic performance results are shown in Table 1. The experimental results 1 are plotted with the doping agent addition position (time) as the abscissa, and the emulsion sensitivity (S) as the ordinate. , To obtain the sensitivity (S) with the dopant addition time change curve, such as.
Table 1A series of emulsion photographic performance results \ average particle size d after emulsification of positional primary gum solution emulsification process (%) performance 80 points sensitization rate 1 sensitivity (S) the addition of ffi gall hybrids position cross-field curve Degree (S) lame sleeves add 1: cross curve. 3.2 The increasing trend of pure bromine cube emulsion B series.
We know that the basic sensitivity (S) of the emulsion is determined by the number of latent image centers formed, and the formation of the latent image centers is determined by the number of effective photoelectrons (or photoelectron lifetime) absorbed by the emulsion. If the photoelectron lifetime is long, it is beneficial The formation of latent images improves sensitivity. However, the presence of positive holes in the emulsion particles will shorten the photoelectron life and cause a certain desensitization. How to extend the photoelectron life is an important means to improve the sensitivity. The addition of ruthenium salt () is to extend the life of the absorbed photoelectron. As a shallow electron trap dopant, ruthenium salt () can temporarily capture photoelectrons, extend the life of photoelectrons, and increase the chance of combining with interstitial silver ions (Agi +), which facilitates the reaction of Agi ++ f. In this process, the nail salt () serves as a good electron donor, and the interstitial silver ion (Agi +) is an electron acceptor, which effectively carries out photoelectron aggregation and avoids recombination with positive holes, which is conducive to latent image Form, increase sensitivity (S).
When nail salt () is added to the nucleation stage, the shallow electron trap formed is deep inside the emulsion particles. When it captures photoelectrons, it causes more photoelectrons to flow into the interior from the outside of the particles, which is easy to form internal sensitive centers, resulting in photoelectrons on the surface of the particles. The reduced number affects the photoelectron efficiency, which is not conducive to the formation of latent images on the surface and causes desensitization; on the other hand, due to the addition of ruthenium salt () to the nucleation period (position 3), the sensitivity of the prepared emulsion is low (S = 2.6), repeat The experiment has the same result, we think it is mainly due to the small particles (0.307um). The author believes that it may be because of the addition of ruthenium salt (), the introduction of complex anions (Ru (CN) 6)), which affects the adsorption of bromide ions on the surface of the crystal nucleus, changes the degree of ion supersaturation in the solution, resulting in an increase in the number of crystal nucleus, The resulting emulsion particles are small.
As we can see, the emulsion sensitivity (S) with the increase in the amount of ruthenium salt () increases first and then decreases, indicating that as a shallow electron trap dopant, the amount of nail salt () added is too small, The effect of the shallow electron trap is small, and the increase in sensitivity (S) is not obvious. As the amount of ruthenium salt added increases, the effect of the shallow electron trap becomes greater and greater, and the sensitivity continues to increase and reaches an optimal value. Continue to increase the amount of nail salt, it will cause the following reaction too much, 4Agi ++ 4Ag4Ru (CN6, reduce the number of silver ions on the surface of the crystal, reduce the latent image formation efficiency, resulting in reduced sensitivity. Reflected in the middle with ruthenium salt () With the increase of the added amount, the sensitivity (S) shows a trend of first increasing and then decreasing. Therefore, we believe that the optimal amount of ruthenium salt is 5.0X1 (T8 ~ 5.0XHT7mol / mol * Ag. For pure bromine cubic emulsion, Through the doping experiment of ruthenium salt (K4Ru (CN) 6p, we obtained the following points: the optimal addition time of ruthenium salt (IQRiCNW) dopant is the late stage of emulsification, that is, the particle formation is 80 ~ 95%; the dopant is the best The dosage is 5.0 Father 1-8 ~ 5.0 Father 1-7111 丨 / 111 丨. Eight §; The introduction of ruthenium salt can increase the sensitivity by 20-40%.
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