Reusable phosphor film?

<p>So, in the world of radiography one can (and many do) replace film with reusable phosphor plates. They are exposed creating a latent image in the plate, put into a reader where the latent image is read, and then the plate is erased. The plates are flexible and can be quite large. They currently only work with X-rays, however.</p>

<p>The readers are very expensive, but it would be interesting to see a can of 35mm film with a phosphor strip or 4x5 pieces of phosphor film. One would also need a small (and hopefully less expensive) dedicated reader for the smaller strips and pieces. Fujifilm makes phosphor plates for radiography, BTW. </p>

<p>I am amused at the idea of people using 4x5 cameras and film SLRs loaded with reusable film. OK, I am not amused enough to invest money in the idea, but I am amused enough to mention it on the internet. If people at Fujifilm feel like coming up with this system, more power to them. Would anyone else want rolls of reusable film for their cameras?</p>

<p> </p>

<p>In almost all conventional (ie, non-laser) circumstances, phosphors only emit radiation of longer wavelength than the input (ie, excitation) radiation. Thus, a red-sensitive phosphor can usually emit only near-IR light. Unfortunately, the lower the energy of the emitting metastable state, the more likely that state will undergo a radiationless transition to the ground state.</p>

<p>In other words, NIR emitting phosphors tend not to be usable for image storage, because they need to get rid of the energy as a photon before it turns to heat. They are more often considered as fluorescent, not phosphorescent compounds. Because of this, I think you are going to have a major problem finding suitable materials for your concept. OTOH, I have heard many people say that they consider the CCD or CMOS array in digital cameras as "reusable film".</p>

<p>;-)</p>

<p>Tom M</p>

<p>An X-ray photon has considerably more energy than a light photon. When it exposes one of the BaFBr:Eu2+ phosphor grains, it causes an electron to jump up to a higher orbital where it will stay for awhile. These electrons stay put until they are excited by a HeNe (red) laser. The red photons have just enough energy to shake the electrons loose, They then drop back to their original orbitals and emit some blue light. This blue light is read by a scanner. I don't know how long the latent image lasts, but I would not be surprised if it faded in a few hours. This is not a problem with x-rays that are read minutes after exposure. </p>

<p>There are no known storage phosphors that work effectively with the low energy levels of light photons. To make a color film, you would need three of them that are sensitive to light photons with different energies. </p>

<p>Let's say you could find a storage phosphor that would work with light photons. You might be able to produce a monochrome system that requires an expensive laser scanner to read the images. You might find a niche market in sheet film sizes. I wouldn't bet on it. </p>

<p>One small modification to:</p>

<p><em>"...There are no known storage phosphors that work effectively with the low energy levels of light photons...."</em></p>

<p>There are moderately long-lived (ie, a few minutes) phosphors that can be excited by low intensity blue and near UV light, just not with low intensity (ie, no 2 photon excitation) red excitation light. An example of the former are the toy stars that glow in the dark which are usually used for kids' ceilings.</p>

<p>Tom M</p>

<p>So, phosphors likely won't work for photography, but I do like the concept. When I saw "It works like film, but is reusable" I was intrigued. </p>

<p>CCDs and CMOS are indeed much like reusable film, but you can't economically retrofit most film cameras with a chip. </p>

<p>Info at - J. Vac. Sci. Technol. A <strong>20</strong>, 1091 (2002); doi:10.1116/1.1463082 (<em>4 pages</em>)</p>

<p><em>"A number of phosphor films have been synthesized with the particle sizes ranging from 2.5 to 25 μm and film thickness ranging from 85 to 1100 μm, and measurement results of x-ray conversion efficiency and spatial resolution in terms of modulation transfer function are presented." - <a href="http://avspublications.org/jvsta/resource/1/jvtad6/v20/i3/p1091_s1?isAuthorized=no">http://avspublications.org/jvsta/resource/1/jvtad6/v20/i3/p1091_s1?isAuthorized=noIf</a> </em><br>

<em> </em><br>

<em> </em><em>If we assume a nominal 10 micron particle size, and 100% coverage of the emulsuion that ~= 2500 particles per inch of 'potential resolution". For 4"X5" that's 125 Mega-thingies :o) Not half bad. </em><br>

<em> </em><br>

<em> Jim</em></p>

<p>Jim, don't forget that even if a similar film sensitive to red light existed, most phosphors films are highly scattering in the visible light. All that I have ever seen look milky white, not transparent - kind of like the front of an old-fashioned CRT TV or monitor. </p>

<p>One of the reasons that they can get such high resolution for X-rays is that scattering is much less for x-rays than visible light. An infinitely narrow pencil of incoming visible light would be scattered over a region about equal to the thickness of the film. Thus, at best, the resolution estimate for visible light should be based on 85 micron "thingies" ;-) , not 2.5 to 25 micron "thingies". </p>

<p>Cheers,</p>

<p>Tom M</p>

<p>These plates certainly can look similar to the naked eye, but they are made out of very different materials and work completely differently. In particular, a CRT phosphor puts out light immediately after being hit by the electron beam, whereas these storage phosphors don't emit light (at least, the light of interest) until they are first hit by x-rays, and then, after minutes to an hour or so, are illuminated with a red laser. It is only then that they emit visible light.</p>

<p>Tom M</p>

<p>Curses, @ 85micron pitch, were down to 2 Mega-thingies!<br>

Tom just unmade my day :o(<br>

Good observation; made me follow up more reading. TY.<br>

Jim</p>