Talk:Fluorescence

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[edit] More?

i miss information about fluorescence used for blacklight active pictures/paint colors. Paniq

Ditto. There is a stub called Blacklight paint (IMHO it is too specifically titled). See the talk page there. Splarka 07:13, 17 August 2005 (UTC)

how to understand the Stoke's shift in the solid state?

[edit] Traffic Signs

What about traffic signs? Do they employ fluorescent materials? 24 August 2006

Not the ones I have seen. They generally use corner cubes, which reflect light directly back at the source. A normal mirror would bounce the light away from the source. Since the driver's eyes and the headlights are close together, they appear to be highly reflective. In stop signs the cubes are generally made of some sort of glass. Larger versions of the same basic concept make the plastic "cat eye" reflectors you likely have seen, the back of the disk consists of moulded half-cubes. Maury 22:06, 31 August 2006 (UTC)

[edit] Definition for Quantum Yield vs. Quantum Efficiency

I'm a little confused about terminology and in browsing the web I see the world is too. Quantum efficiency and quantum yield seem to be used interchangeably in some settings.

I thought that quantum efficiency was defined as the ratio of emitted photons to successfully absorbed photons and could also be defined in terms of the radiative emission constant to the sum of rate constants for all relaxation paths.

I thought The quantum yield alternatively was the product of the probability of a photon incident on the molecule being absorbed (molar extinction coefficient) with the probability of emission given absorbtion (quantum efficiency).

An analogy for the difference might be made considering an opperation of recieving and throwing balls between to parties. Imperically, my efficiency for throwing balls could be estimated as the ratio of the number of times that I throw it back to doing something else with it (eat it, burn it, drop it, hand it to someone etc.) But if your curious about how many balls you need to throw at me to get one thrown back, you must consider how good I am at catching things that are thrown at me!

[edit] Fluorescence of quantum dots

In general, the shining of quantum dots is not fluorescence. Since it is a semiconductor, not a molecule, it does not have electronic levels. According to Jablonski diagram, fluorescence is a process that occurs from the lowest sublewel of the lowest excited electronic level. So fluorescence can not occur in semiconductors. The process, in which quantum dots emit photons, could be referred as luminescence, or photoluminescence (since it is induced by light).

[edit] Discrete frequencies vs. Continuous Spectrum

I don't quite understand fluorescence. If the element which absorbs the UV, then emits visible light is a solid (e.g. solid paint on fluoro lights), why is the visible light emitted only certain discrete frequencies, not a continuous spectrum, like if you heat the solid??

black body radiation is a very different process than fluorescence, so it should not be entirely surprising that it differs in some aspects. In the case of fluorescence the light is being given off by the change in energy levels of the electrons. Incoming photons, UV in your example, bump the electrons up to an energy level above that of what it will eventually give off, say orange. The electrons then fall towards that state over a period of time, giving off energy as photons or into the material itself as heat. In either case the energy given off is too small to notice to the naked eye. This process continues until it reaches the "magical state" that gives off the visible photon, which comes out as the orange light you see. Maury (talk) 20:33, 3 March 2008 (UTC)