I've been doing a lot of work with white LEDs recently, and me being the ham-fisted sort that I am, it was inevitable that I'd manage to break one sooner or later. Not electrically, that would be far too easy, but mechanically. That day arrived today when I managed to snap the top off a Lumileds Luxeon III.
White LEDs apparently work by using a source of blue light and then a phosphor on top of that to convert some of the blue light to yellow, giving a white-ish result. What I discovered is that if you have access to the inside of the LED, you can actually scrape off the phosphor using a precision tool such as your fingernail.
Here's a picture of an unbroken LED:
And here's what it looks like with the top off and after a bit of fingernail-scraping:
You can see the semiconductor die under where the yellow blob of phosphor used to be.
Much to my surprise it still worked even after all this abuse. Here's a picture of the normal and broken LEDs lit next to each other.
The colour contrast is quite obvious: the one with no phosphor gives out a rather nice colour of blue light. I don't suppose it'll last long, open to the elements like that, though. Hopefully this page will satisfy the curiosity of anyone who might be tempted to pull one apart and save them an expensive experiment!
Chris Jones, 28 October 2003