A Visualising visible light Fluorescence

[aaaaautumn]

Hi all,

I am new to physics forum and would appreciate all your input in this topic. I am trying to understand if an object fluoresces under UV light it is possible it may also Fluoresce under visible light? additionally would it be possible using band-pass filters (device that passes frequencies within a certain range and attenuates frequencies outside that range) to narrow the band of visible light and observe this fluorescence?

I am a physician and not a physicist so do excuse my ignorance if Im talking rubbish :)

 

[DrClaude]

Yes and yes. We are more accustomed to fluorescence from the UV into the visible because it is an obvious phenomenon, but fluorescence from the visible to the visible can occur, but it is usually harder to distinguish from the object being a certain color. Using filters would be one way to observe this fluorescence.

 

[sophiecentaur]

, but fluorescence from the visible to the visible can occur,

And why not from visible to non visible frequencies? All that's required is appropriate energy levels in a substance. When light of a certain frequency is 'absorbed' by a pigment then the energy can be at an IR frequency. Some light is absorbed and produces a colour by frequency selective reflection.

I suggest that fluorescence is actually a special case which makes certain surfaces look odd or noticeable under the right lighting conditions. What you see in other situations could often be due to a similar mechanism.

 

[Baluncore]

On photon energy grounds, the excitation light must have a shorter wavelength than the emitted light. That limits the excitation when it comes to visible - visible fluorescence. A blue light can excite a red fluorescent emission, but not the other way around.

There are only a handful of "Dayglo" or "dayglow" pigments that fluoresce in the visible under UV light.

 

[aaaaautumn]

thank you @DrClaude @Baluncore @sophiecentaur

If I can be more specific I am conducting research on composite resin which is used in dentistry. In UV light (sweet spot of 385nm) it fluoresces and can be seen in the visible blues spectrum, this allows us to identify what is composite from what is say tooth structure when performing procedures. However UV light is something we try to limit using in healthcare due to adverse effects on the skin and cancer risk, I am trying to figure out if I can use visible light instead of UV and then use a relevant band pass filter to obverse its fluorescence. Is this a crazy idea? is there a process by which you can find out if an object fluoresces in visible light and the wavelength that fluorescence is most visible at? Any other ideas using the same concepts is very welcome and would heavily aid in my research project.

Thanks again

 

[sophiecentaur]

is there a process by which you can find out if an object fluoresces in visible light and the wavelength that fluorescence is most visible at?

Firstly I'd suggest that the original dose of UV that cured the resin (several seconds of exposure there) would need to be many times the dose needed to see some fluorescence. So probably no worries if you read up the Health and Safety situation in the use of the uv setting resin. And the uv source could be a lot less bright.

As for finding an alternative light source for the effect, I'd imagine that you won't find a lower frequency that would cause actual fluorescence. For a start, the frequency shift is very small if the colour you get is blue. But the same frequency that is produced by fluorescence is likely to be a similar frequency that would be absorbed when used as an illumination. A spectrometer could measure a specific visible band and that could spot the presence or absence of that resin. Hand held spectrometers are used by gemnologists to determine the chemicals that are responsible for some gem colours. Somewhere for you to look, perhaps.

 

[Baluncore]

However UV light is something we try to limit using in healthcare due to adverse effects on the skin and cancer risk, I am trying to figure out if I can use visible light instead of UV and then use a relevant band pass filter to obverse its fluorescence.

Blue fluorescence really has you cornered at the violet end of the spectrum. To get blue, you must excite the composite resin with a shorter wavelength, UV or violet. The boundary between near-UV and visible-violet, is usually taken to be the wavelength of 380 nm. Your "sweet spot", of 385 nm, is strictly visible-violet, NOT ultra-violet, UV.
https://en.wikipedia.org/wiki/Violet_(color)

A white LED lamp is typically made from a violet LED emitter, with several visual fluorescent compounds, balanced to make a daylight white, or a warm white light. You might be able to use a violet LED as your excitation source, to emit blue light.
LED sources of 395 nm are cheap, and widely available. They often claim to be UV or "black light" in the advertising, but they are not, they are violet. Have you tried one of those?
An example, used to fluoresce blue is; https://www.ebay.com.au/itm/295950654406

Note that "grow lights", used for hydroponics, could employ a violet LED, but they may actually be purple=blue+red, which is useless for blue fluorescence.
https://en.wikipedia.org/wiki/Grow_light#Fourth_generation:_Light_emitting_diodes_(LEDs)