UV nail lamps for EPROM

The coating is not opaque even to visible. Shine a flashlight through a fluorescent tube and you will notice that visible light passes through. Long wave ultraviolet does also.

If you go to Home Depot, or some such place, you can buy one of those horribly inefficient "black light" bulbs that is really an incandescent bulb with an envelope made of Wood's glass

formatting link

Break the bulb so you have some pieces of the Wood's glass to play with. Get a piece of something that is highly fluorescent, like one of those bright orange price labels on some item of food. Hold up a piece of Wood's glass to an ordinary visible fluorescent tube (compact fluorescents work), and let whatever comes through the Wood's impinge on the label. The label will fluoresce. You may have to make a shield of a piece of cardboard with a hole in it so most of the visible isn't shining in your eyes, but the piece of Wood's glass covers the hole, through which whatever is transmitted shines on the label. Actually, blue light, such as from a blue LED will also fluoresce the label, but the Wood's glass filters out most of the blue and passes primarily long wave UV. The fact that the label fluoresces indicates that some long wave UV is emitted by the fluorescent tube.

A good test of the reaction of silver chloride to various colors of light would be to use several ultra-bright LED's, say, orange, yellow, green, and blue. Shine them on the silver chloride. The good thing about using these light sources is that they are pseudo-monochromatic. There is a narrow emission band, and no out of band energy to confuse the results.

Thanks. I'm surprised that an ordinary incadescent gives off any UV.

Actually, my goal was to make a poor man's absorption analyzer to measure the concentration of silver ions in a solution. Adding salt converts the ions to insoluble silver chloride, and the density of the dispersion indicates the ion concentration:

Ag(+) + OH(-) + Na(+) + Cl(-) --> AgCl(ppt) + NaOH

I was looking for a light source that would not decompose the silver chloride to silver metal and chlorine gas during the measurement. After the measurement is complete, I plan to illuminate the solution with UV and measure the absorption of the silver metal particles to see if that gives any useful information:

2AgCl + 2UV --> Ag(s) + Cl2(g)

It looks like infrared or a plain red led may work for the initial measurement, especially if I keep the intensity very low. This produced a pleasant several days of research on lock-in detection methods, and a very interesting SPICE analysis of two of the most common methods. It looks like a simple inverter driving a CMOS SPDT switch will do the job quite nicely. Most sources indicate the inverter needs 0.1% or 0.05% resistors to get good balance, but the SPICE model shows the inverter balance doesn't have to be perfect and it will still give good results.

Thanks for your interesting post.

Regards,

Mike Monett