UV nail lamps for EPROM

[Don Klipstein]

[... very good info on UV]

Thanks for posting this information, Phantom.

I have a question. I notice that silver chloride turns black when
exposed to the light from ordinary office flourescent lights.

This reaction occurs when a UV photon forces a chlorine ion to give
up an electron, which then converts a silver ion to a metal atom.
The metal absorbs visible light and appears black. The reaction is
quite strong with only two overhead lights. Here is a description:

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

The same reaction occurs outdoors in sunlight. Since the short wave
UV cannot penetrate ordinary glass, I assume the UV in this reaction
is long wave UV.

However, manufacturers of flourescent lights, such as GE, insist
that no UV escapes from their product.

They probably mean the main strong shortwave UV wavelengths of
low pressure mercury vapor.

But obviously a great deal does escape.

The 365-366 nm cluster of mercury spectral lines does go through most
glass well, and is a weak but slightly significant spectral feature of
fluorescent lamps. Exception: Triphosphor lamps (including most compact
fluorescents) of color temperature rating 3500K or higher usually in my
experience have a blue-emitting phosphor ingredient that utilizes that UV
wavelength.

Maybe silver chloride responds to the 404.7 nm violet wavelength of
mercury, or has slight response to the violet-blue 435.8 nm wavelength of
mercury that is strongly present in the light from fluorescent lamps.

http://coolcosmos.ipac.caltech.edu//
cosmic_classroom/classroom_activities/ritter_bio.html

indicates silver chloride reacting to visible blue and violet light as
well as to UV.

http://photography.about.com/library/weekly/aa011402b.htm

also indicates ability of blue and violet visible light as well as UV to
cause silver chloride to do its photochemical reaction.

Both of these note Ritter discovering UV via its great ability to cause
the photochemical reaction in silver chloride.

Do you have any idea how the UV gets through the phosphor coating?

A lot of fluorescent lamps have phosphor coatings that do not absorb
longwave UV.

- Don Klipstein ([email protected])

 

[Mike Monett]

They probably mean the main strong shortwave UV wavelengths of low
pressure mercury vapor.

The 365-366 nm cluster of mercury spectral lines does go through
most glass well, and is a weak but slightly significant spectral
feature of fluorescent lamps. Exception: Triphosphor lamps
(including most compact fluorescents) of color temperature rating
3500K or higher usually in my experience have a blue-emitting
phosphor ingredient that utilizes that UV wavelength.

Maybe silver chloride responds to the 404.7 nm violet wavelength
of mercury, or has slight response to the violet-blue 435.8 nm
wavelength of mercury that is strongly present in the light from
fluorescent lamps.
http://coolcosmos.ipac.caltech.edu//cosmic_classroom/classroom_activities/r
itter_bio.html

indicates silver chloride reacting to visible blue and violet
light as well as to UV.

Interesting. I posted a link earlier from the same url that stated
pretty much the same thing - silver chloride is not very sensitive
to red light but is increasing sensitive to shorter wavelengths:

http://coolcosmos.ipac.caltech.edu//cosmic_classroom/classroom_activities
/ritter_example.html

http://photography.about.com/library/weekly/aa011402b.htm

also indicates ability of blue and violet visible light as well as
UV to cause silver chloride to do its photochemical reaction.

Another link that confirms this is by Saul Bolaos. He describes how
to make a gelatin emulsion of silver chloride to print pictures on
irregular curved shapes such as an egg. He states the silver
chloride emulsion is insensitive to red light:

http://www.costaricacoffeeart.com/alternative_photography.php

So a red led may have little effect on silver chloride.

Both of these note Ritter discovering UV via its great ability to
cause the photochemical reaction in silver chloride.

A lot of fluorescent lamps have phosphor coatings that do not
absorb longwave UV.

That makes good sense. I notice the reaction is much stronger with
fluorescent than with incandescent lamps. But that may depend on the
manufacturer - Roger Hamlett posted information showing GE lamps
have very little emission beyond 370nm:

http://www.gelighting.com/na/business_lighting/education_resources/learn_
about_light/distribution_curves.htm

- Don Klipstein ([email protected])

Thanks for the good information, Don.

Regards,

Mike Monett

 

[The Phantom]

[... very good info on UV]

Thanks for posting this information, Phantom.

I have a question. I notice that silver chloride turns black when
exposed to the light from ordinary office flourescent lights.

This reaction occurs when a UV photon forces a chlorine ion to give
up an electron, which then converts a silver ion to a metal atom.
The metal absorbs visible light and appears black. The reaction is
quite strong with only two overhead lights. Here is a description:

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

The same reaction occurs outdoors in sunlight. Since the short wave
UV cannot penetrate ordinary glass, I assume the UV in this reaction
is long wave UV.

However, manufacturers of flourescent lights, such as GE, insist
that no UV escapes from their product. But obviously a great deal
does escape.

Do you have any idea how the UV gets through the phosphor coating?

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(http://en.wikipedia.org/wiki/Black_light). 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.

 

[Mike Monett]

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(http://en.wikipedia.org/wiki/Black_light).

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

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.

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