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You might have seen the absorption spectrum of ruby: it has distinct absorption peaks near 400nm and 550nm. Looking at its absorption graph, one could expect some fluorescence when excited from a ~450nm source - not as good as from a 400nm source, but absorption is still significant.

I've compared the fluorescence of a ruby rod when illuminated by 405 and 450-460nm LEDs. It appeared that fluorescence from a blue LED is extremely weak, many dozens of times weaker than from a 405nm LED. But from the absorption graph, the difference is not that great.

Does anyone have insight on why there is absorption, but almost no fluorescence of ruby when illuminated by a 450-460nm source? The same for a 532nm laser source (i.e. narrow band this time, but slightly higher energy than needed) - there is absorption, but almost no fluorescence.

Has someone seen fluorescence activation spectra in the literature? On the ruby state diagram I see that the main "up" transitions are activated by 420nm and 550nm photons, but it is not clear how wide the peaks are for crystalline (= almost perfect) synthetic ruby.

The goal is to find current / future semiconductor sources which would allow DPSS Ruby laser.

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BarsMonster
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2 Answers2

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So the fluorescence process is not a single step as are absorption or Emission with set energy levels. Fluorescence occurs in combination with radiation, energy loss in form of heat as well as phosphorescence sometimes. these all are depicted by a Jablonski Diagram whose picture is; https://prnt.sc/h8dnxy https://en.wikipedia.org/wiki/Jablonski_diagram

The internal conversion you see between absorption and fluorescence takes up energy and hence there is a lag of energy and fluorescence and absorption spectra don't match up. Similar the case for higher LED wavelengths. The issue with comparing fluorescence and absorption spectra is that they are two completely different processes with different mechanics. You cannot compare the two without taking in account the intricacies of the full process, have a look at the plots once again. You'll observe that even with excited states there is decline of energy. All this energy is also lost as heat or vibration which is not measured in a fluorescence spectra. Try comparing two fluorescence spectra that would give a more accurate picture.

Kyle Kanos
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user174925
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From purely empirical plain sight observation, my synthetic laser ruby crystal glows bright red when excited with a 520nm green laser and also with a 450nm blue laser. The red emissions are quite obvious in broad daylight when using excitation laser power of 1 watt or greater.

user309900
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