Fluorescence and green light.

[Guest Tribute]

I made an interesting observation when fooling around with my green laser pointer around the house. In my basement there are some 70's colored posters that glow in a black light. As I ran my laser over these posters, I noticed the paint changed the color of the light. I paid more attention this time and pointed the laser at individual segments of paint. It seemed that only the red and orange paints converted the color. A few other red and orange items that respond to a black light convert the color as well. I've come to a conclusion about this effect but I wanted to make sure it is correct as my internet searches have come up with nothing regarding green lasers and fluorescent paint. From what I HAVE found, I have concluded this:

 

 

The fluorescent paints contain phosphors that take in UV light and re-emit them as visible light. They do this by the electrons in the phosphors absorbing the light and rising up to a certain orbital and then dropping back down, releasing the light that is the equivalent wavelength of the orbital. When the green laser light is shined on a red or orange fluorescent paint the same thing occurs as when UV light hits it because it emits enough energy to charge the electrons. However, on bright green and yellow paint this does not occur because the energy required to excite the electrons, enough to produce the higher energy colors, is not present.

 

Is this a sound assessment of what is occuring? Is this a relatively unique observation regarding the green laser? I have a few Ideas regarding labs I could do relating to this, however, if any of you have any ideas that would be helpful as well because I am using this topic for the IB Essay I must do in order to receive my diploma.

[swansont]

The fluorescent paints contain phosphors that take in UV light and re-emit them as visible light. They do this by the electrons in the phosphors absorbing the light and rising up to a certain orbital and then dropping back down' date=' releasing the light that is the equivalent wavelength of the orbital. When the green laser light is shined on a red or orange fluorescent paint the same thing occurs as when UV light hits it because it emits enough energy to charge the electrons. However, on bright green and yellow paint this does not occur because the energy required to excite the electrons, enough to produce the higher energy colors, is not present.

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You're missing a step. If it was just absorption-emission, the photon's energy would be the same and thus the same color.

 

What happens is that the absorption happens, and there is some relaxation in the molecule - goes to a lower state by e.g. increasing vibrational or rotational energy - and then it gives off a lower energy photon.

 

Also, technically, a phosphor is a material that retains the excitation energy for a period of time (e.g. in a metastable state), so it glows in the dark. A fluorescent material gives the energy back quickly - it gives the "black light" effect but won't glow more than a fraction of a second after you turn the light source off.

[Guest Tribute]

So is the increase in vibrational or rotational energy in the form of heat? If so, would this be measurable, or too miniscule?

[swansont]

So is the increase in vibrational or rotational energy in the form of heat? If so, would this be measurable, or too miniscule?

 

It should show up as an increase in temperature, and thus increased blackbody radiation (i.e. mostly IR) Whether or not you can see it easily would depend on how much energy is lost in the relaxation.

 

From another point of view - energy is conserved. You shine a certain power of light on the fluorescent material, you get some back at the lower wavelength. The rest has to have gone somewhere - the material will heat up.