Some time ago, my eldest son decided to make glow-in-the-dark pigments by doping strontium aluminate with rare earth elements. After a bit of trial an

Building a phosphorescence detector - lcamtuf’s thing

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2024-11-28 02:00:03

Some time ago, my eldest son decided to make glow-in-the-dark pigments by doping strontium aluminate with rare earth elements. After a bit of trial and error, he succeeded — and the relative simplicity of the process made me wonder if there are any naturally-phosphorescent materials in our homes.

Of course, we’re not surrounded by items that exhibit strong and long-lived phosphorescence. Still, perhaps the effect is too faint or too brief to see with a naked eye? The internet offered no good answers, so I decided to investigate on my own.

In theory, the idea was simple: place samples in a lightproof container, shine a UV light on them for a while, and then measure any residual glow with a photodiode circuit — as discussed in one of the recent posts.

The main gotcha is the inherent trade-off between sensitivity and response speed. A photodiode with a large active area is more sensitive, but has a high junction capacitance, making it harder to capture short-lived events. In contrast, a small photodiode is fast, but needs more amplification; faint readings are more easily drowned out by noise.