indigofuzzy - 17-7-2010 at 06:30
Quite by accident, I discovered that phosphorescent materials can be made from boric acid.
I had heard of boric acid's use as a flux, so several months ago, I melted some solder scraps under a thin layer of boric acid. I set the experiment
aside and forgot about it for a while. Last week, I turned on a blacklight in the room where I had left the experiment and noticed it fluorescing.
Upon switching off the blacklight there was a brief (0.5s or so) afterglow.
I experimented to find out what was causing the phosphorescence. I initially thought that maybe the tin or antimony from the solder was acting as a
dopant, so first I melted more boric acid over solder scraps, with the same effect. Then I meted some in an aluminum dish similar to the one I had
melted the solder scraps in, and it still phosphoresced. I melted some on a strip of copper, and this phosphoresced. So I started to wonder if the
metals were really doing anything at all. So I tried meting boric acid in a glass tube. Lo and behold, the same brief afterglow.
I found this interesting enough to start experimenting with adding in metal salts to see if I could extend the glow time. Copper salts very slightly
increased the glow time. This morning, I tried Calcium hydroxide. WOW. In a dimly lit room, I can see the phosphor I produced continuing to glow for
approximately 10 seconds.
Next step: seeing what ratio of Ca(OH)2 to B(OH)3 produces the longest glow lifetime.
I noted something else unusual, with the ultraviolet light switched on, the phosphor fluoresces a pinkish-yellow color, but the glow produced is
almost the same green as ordinary zinc sulfide “Glow-in-the-dark” items.
I'm curious to know if anyone else had heard of fused boric acid being phosphorescent. According to wikipedia, boric acid decomposes on heating into
metaboric acid and then pyroboric acid, so it's likely that one or both of these are responsible for the phosphorescence.