SRAD emulsions

I noticed that some emulsions posted on this forum have a first step where the AgNO3 is combined with Ammonia.

The emulsions I make are very fine grained (grain sizes less than 20nm) and are intended for holography. The sensitivity of my (red sensitive) emulsion is very low at the moment and has to be increased before exposure by immersing the emulsion into a solution of dilute developer. I would like to increase the sensitivity of my mix without using the gold sensitizer because it causes grain growth.

My question is: Is the Ammonia step done to increase the sensitivity of the emulsion? If that is the case, does the SRAD procedure encourage grain growth or is it still possible to make ultra fine grain emulsions with it?

Hans;

SRAD emulsions can be made in virtually any size, but the Ammonia is used to enhance growth rate of the grain and to induce iodide to be more evenly mixed in the grain (if present). It also tends to increase fog.

Gold increases grain size partly as a function of ripening and is dependant on the vAg of the emulsion when the gold is added.

Generally, the faster you add the silver, the finer the grain (and more uniform), and the longer you keep an emulsion hot, the larger the grains become.

PE

Ah, thank you. So, I guess that SRAD is a no-go for my holographic emulsions.

Not necessarily. You just may want to use a small amount of ammonia, or an ammonium halide salt in the make, or you may want to make a double run. I have made 0.2 micron cubes with a mean deviation of +/- 0.01 microns by double runs. It just takes patience and some investment in equipment to do these things.

If you use an ammonium halide salt, then a short cycle adding alkali and then acid will give you a controlled treatment with ammonia. The SRADs described here use a relatively massive amount of ammonia for the digest and during the run.

PE