- Aug 5, 2010
Nice summary - thanks, @Nick_GIt indicates that the sapphire contains some chromium, and the iron content is low enough not to quench the fluorescence. If the iron/titanium impurities (these are what colour sapphires blue) weren't there your sapphire would probably be a nice pink colour.
It's the chromium content in rubies that causes the red colour, and if there is very little iron they will fluoresce bright red in LW UV. It's also why the best quality rubies seem to glow from within when viewed in bright sunlight.