What is Fluorescence: Definition and 73 Discussions

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. The most striking example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the spectrum, and thus invisible to the human eye, while the emitted light is in the visible region, which gives the fluorescent substance a distinct color that can be seen only when exposed to UV light. Fluorescent materials cease to glow nearly immediately when the radiation source stops, unlike phosphorescent materials, which continue to emit light for some time after.
Fluorescence has many practical applications, including mineralogy, gemology, medicine, chemical sensors (fluorescence spectroscopy), fluorescent labelling, dyes, biological detectors, cosmic-ray detection, vacuum fluorescent displays, and cathode-ray tubes. Its most common everyday application is in energy-saving fluorescent lamps and LED lamps, where fluorescent coatings are used to convert short-wavelength UV light or blue light into longer-wavelength yellow light, thereby mimicking the warm light of energy-inefficient incandescent lamps.
Fluorescence also occurs frequently in nature in some minerals and in many biological forms across all kingdoms of life. This is sometimes referred to as biofluorescence to indicate that the fluorophore derives from a living organism (as opposed to artifically adding a dye or stain). However, in many cases the substance may be fluorescent even if the organism is dead, thus fluorescence is still the preferred term.

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  1. aaaaautumn

    A Visualising visible light Fluorescence

    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...
  2. FeatherGlow

    I Is Fluorescence Possible in Twilight?

    Earlier this year I saw what appeared to be a large glowing bird at twilight. The normal explanation for this is bioluminescent fungus contaminating a bird. I’m wondering if the effect might actually be a blue light effect where a fluorescent bird only appeared to glow because of the lighting...
  3. RooneyChemistry

    Fluorescent Sample with Cuvette but not with Plate -- Why?

    I am doing an assay where the formed compound is fluorescent when I use a cuvette in a fluorometer, but not when I put the same sample into the well of a 96 well plate. Why is this? The fluorometer reads from the top and the plates I am using are 96 well plates, black, flat-bottomed well...
  4. A

    I Can visible light cause fluorescence in colorful objects?

    https://en.wikipedia.org/wiki/Fluorescence You normally heard of Fluorescence coming from UV which make the objects glow. But visible light can also cause fluorescence. When you hit a colorful sample with a 532nm laser, there is fluorescence in the visible spectrum (as seen in Raman...
  5. G

    I X-ray fluorescence photons question

    Tentatively, I ask in this forum for a qualitative pointer to what end effects one might expect when a gamma energy photon energizes an atom of a substance, and causes fluorescence. It relates to a practical endeavour about using a PIN diode as an X-ray detector, where the device considered...
  6. T

    Fluorescence of a laser vs its pulse duration

    When working with a pulsed laser (nitrogen), How can the fluorescence lifetime be longer than the pulse of the laser? Thanks for any explanations
  7. pallab

    A Why do Eu doped phosphors show fluorescence property without singlet?

    As it is mentioned fluorescence is a singlet to singlet transition and this is the reason that fluorescence is a fast process. now consider the Eu doped phosphor material where 5D0--->7F2 and other transitions show the prominent intensity peaks in down-conversion process. those are not singlet...
  8. dykuma

    A mathematical description of the physics behind Aurora?

    Maybe a bit of an odd question (not really sure where it would belong on this site to be honest), but I was wondering if anyone can explain, or at least knows of a source that explains in a quantitative way, the physics behind aurora? Now I've seen websites like this that discuss conceptually...
  9. littledog

    Why is it difficult to stain dormant bacteria with Nucleic acid dyes?

    I found that it's difficult to stain dormant bacteria or bacteria in lag phase with Nucleic acid dye like SYTO9/SYBR Green Ⅰ, does anyone know why? DNA 3D structure too complex? DNA binding protein too much? Low material transport efficiency in bacteria? Or anyother factors? Is there any...
  10. M

    I Confused about fluorescence at resonance

    Hello! I am a bit confused about a resonance signal that is obtained by measuring the fluorescence signal from overlapping a laser beam with some atoms. Based on the signal shape, the maximum number of counts corresponds to the resonant frequency of the transition (ignoring for this questions...
  11. K

    Deconvolution of fluorescence spectra

    I am trying to make a deconvolution of fluorescence spectra in Matlab. The original spectra is the yellow graph in the figure below. The other two graphs are Cauchy distributions, x and y, that I have manually added to the plot. I would like to write a program that could do this automatically...
  12. L

    I Is it possible for water to exhibit fluorescence?

    Why is it impossible to induce fluorescence in water? Is it because of missing electrons that can do the fluorescence process, or other reasons?
  13. Graeme M

    How does ultraviolet photography (fluorescence) work?

    I was reading my latest Reader's Digest in which appears an article about ultraviolet photography. The article explains that this kind of photography utilises a technique known as ultraviolet induced visible fluorescence. The article says that the technique allows flowers to reveal spectacular...
  14. patric44

    I Is this just a normal fluorescence of glass molecules?

    hi guys i recently had built a HV power supply out of an old Flyback transformer i had laying around , i think it produces about 10KV ~ 15KV not very sure but it could arc at about ( 6mm in air ) , and as you can see i tried to connect it to a 15W smal light bulb ( the positive terminal...
  15. L

    Intensity characterization of laser pulses

    754/5000 I am using the fluroescence spectroscopy technique to obtain the fluorescence spectrum of exposed neuroblasts to uv radiation (355 nm) from a Nd:YAG source and I need to characterize the radiation pulses of the laser. Specifically, I use a spectrometer (Avantes brand) with integration...
  16. A

    I Fluorescence from core shell quantum dots

    What is the reason for enhancement in the intensity of emission due to the introduction of a shell in quantum dots? I do understand the blue shift in quantum dots but how does a shell enhance it?
  17. H

    A Single molecule fluorescence microscopy and limits

    I want to ask the limits on the molecule side for single molecule fluorescence microscopy. I am writing a proposal but I lack experimental knowledge since no one in my lab have ever used one. At least how much of an absorption coefficient, with at least how much of a radiative rate is necessary...
  18. bluejay27

    B Can Visible Light Excite Quantum Dots to Emit Fluorescence?

    Quantum dots fluorescence whenever UV light is applied to them. Whenever the UV light is off and visible light hits the quantum dots it posses colors but does not fluorescence. I thought light had to have energy that is equal or greater than the band gap for the quantum dots to emit light. How...
  19. Anton Alice

    Detecting fluorescence via CW or pulsed LEDs

    Hello forums, in the context of a little DIY-project I am planning to build a rudimentary fluorometer, which is actually doing nothing but checking whether an amount of protein is fluorescing or not, and roughly measuring its intensity. A highpower LED is used to excite the protein to the...
  20. S

    Why Fluorescence is detected @right angle to the excitation?

    Hi everybody, I would like to know what would be the best angle (or best geometry) to put the detector relative to the light source in order to observe the emission radiation from the fluorescent materials? As I know the most common geometry used for fluorescence is right angle observation...
  21. F

    Blue Fluorescence and blue color

    Hello, I have read that blue fluorescent dyes do not exist. Why? Optical brighteners do convert UV into blue light but a piece of plastic containing optical brightener dyes appears clear and transparent instead of blue? Why? Does the color of the substance not correspond with the fluorescent...
  22. H

    Looking for the right fluorescent compound

    Hi I'm searching for one or more fluorescent compounds with the following characteristics: 1. High quantum efficiency > 0.85 2. 200-400nm excitation range. 3. Approximately 440nm, 625nm or 678nm emmission range 4. Decent stability (At least 30 days) Does anyone know of a either specific...
  23. R

    Fluorescence Spectroscopy and Stokes Shift

    This is a question on fluorescence spectroscopy so physics/chemistry. What causes a large Stokes shift in the spectra? I know what causes the shift in wavelength, i.e., a relaxation of vibrational states before de-excitation to the ground state, but what actually causes a (very) large Stokes...
  24. O

    Is it possible for an electron to emit more than one photon during fluorescence?

    Fluorescence occurs when an atom or molecule absorbs a photon, promoting a ground state electron to an excited state, and the electron returns very quickly to the ground state, emitting a new photon. The new photon is usually of a longer wavelength because some of the energy is lost to...
  25. patrickbotros

    Explain Different Types of Light Microscopy

    Okay so first I would like someone to add detail to my descriptions of different types of light microscopy. Here's what I know: Brightfield (unstained): standard view of partially opaque, live cells. Brightfield (stained): standard view of colored, dead cells. Phase Contrast: Not sure how it...
  26. G

    Fluorescent lamp: who emits UV?

    Hi everyone, searching on the web about how the fluorescent lamps work, I cannot understand if the UV is emitted by the noble gas or the mercury. For what I understand, both of them ionize, and the UV light is emitted after the collision of the electrons with the atoms, but I would like to...
  27. M

    Why does the rate of transitions depend on the population of the ground state?

    Hi all. I need a help about a stupid thing which is puzzling me! I'm studying a paper where it's described a classical excitation of a fluorophore from a ground state to an excited state. See the attached image! There are two laser beams which act on the sample, the first one which is an...
  28. B0b-A

    Can Pure Water Fluoresce Under UV Light?

    Can pure* water be made to fluoresce if illuminated by some particular frequency of Ultra-Violet light ? [* No chemicals added ]
  29. Y

    Fluorescence of fused silica, quartz and Borofloat 33?

    I am trying to get a glass substrate, which is transparent. However, I need this substrate to have low fluorescence. I know fused silica, quartz and Borofloat 33 are transparent but I don't know which one has the lowest fluorescence. I checked google but can't find any data that directly...
  30. T

    Definition question about atomic fluorescence

    Does atomic fluorescence involve: 1. spontaneous emission (or only), 2. stimulated emission (or only) 3. change in magnetic quantum number $$\Delta m \neq 0$$ ? Thank you. Rarely can I find a definition on the internet. My guess is that atomic fluorescence involves spontaneous emission only...
  31. Y

    How to measure fluorescence intensity time trace?

    I understand that fluorescence intensity time trace is constantly monitor the fluorescence intensity and plot it over time. But the question is at which excitation wavelength? Also, what is the emitted wavelength that is being measured? I suppose it should be two particular wavelengths, but how...
  32. G

    Dichroic mirrors that reflect two wavelengths

    In fluorescence microscopy, dichroic mirrors reflect light under a critical wavelength (used to excite the sample) and transmit light over a critical wavelength (emission light from the sample). Are there mirrors that reflect two different wavelengths of light and transmit the rest? Essentially...
  33. S

    Exploring 488nm LED Options for Fluorescence Activated Cell Sorters

    Why can't I find any LED's at 488nm? I am trying to find a cheaper light source than the traditional argon ion laser for a possible fluorescence activated cell sorter. See link below for schematic. Does anybody know a good retail site for lights in this spectrum I can't find good results with...
  34. N

    Does a CFL Pose a Fire Risk Due to Inductive Load Characteristics?

    As far as I know, Compact Fluorescent Lamp (CFL) is an inductive load. I understand that inductive load doesn't allow an immediate change in current. When the circuit was initially open (through open switch) then became close, the inductive load was energized. So opening again the circuit after...
  35. B

    Question about UV LED fluorescence

    Hello,I'm new to the physics forum.I have a question regarding fluorescence,and I didn't know where to post it exactly,so I decided to do it here... I like growing plants,and am forced to grow them under artificial lights during winter.I am always on the lookout for more efficient lights,that...
  36. TESL@

    X-ray to Microwave fluorescence

    Hello, Is there any specific element that would absorb x-ray and emit radiation roughly in microwave band (not thermal radiation, fluorescence). Or could it be achieved by mixtures and gradual wavelength increase? Thank you.
  37. J

    Biochemistry: Tryptophan fluorescence

    1. A 100-residue globular protein contains two Trp residues, and has two segments with the same 9-amino acid sequence, SSSLWLAAA. One segment is residues 1-9, and one segment is residues 44-53. What would the complete fluorescence spectrum of the protein MOST LIKELY contain? a) It would contain...
  38. B

    Bi-directional transport of light

    In several fiber-optic-based probes in medical imaging fields, the light travels towards an object through an optical fiber (or even free space), interacts with the object and then travels back through the same fiber (or the same path in free space) and is captured by a camera or photodetector...
  39. miraiw

    Could fluorescence quenching be used for making 3D images?

    Looking at the image from this wikipedia article, it looks like there's a selective fluorescing of the quinine dependent on the presence of chrolide ions in the solution. If the concentration of chloride ions in a solution could be controlled into a particular shape, shining a violet laser on...
  40. L

    Upconversion fluorescence

    Hi there, I was looking into two photon fluorescence microscopy and was amazed at the light intensity required for the simultaneous two photon absorption to take effect; as it is, the setup is prohibitively expensive, the laser source is particularly problematic. Are there any compounds that...
  41. A

    Quantum yield: fluorescence spectrum correction

    Hello, I hope all is well, I have a few questions regarding fluorescence spectral corrections. I have run into an issue with corrections on the instrument I'm using. I have obtained spectra for a few compounds where the correction was working properly and achieve the results as expected. When...
  42. C

    Fluorescence diffusion physics problem

    Homework Statement As a simple model, suppose you arrange for the intense bleaching pulse of light to illuminate a cell in a pattern of parallel planes. That is, immediately after bleaching (at time t=0), the remaining fluorescence intensity Θ(x) has the form Θ(x)= C(i) + C(1)sin(2pix/L)...
  43. C

    Fluorescence Excitation and Emission Spectra

    I need help understanding the relationship between the excitation and emission spectra for a fluorescent material. This is not homework. Let's say we have the following graph which plots the two spectra for a given material: Two curves are shown - the excitation spectra and the...
  44. J

    Can we measure the band energy gap from Fluorescence spectra

    Can we measure the band energy gap from Fluorescence spectra? If yes, in what way? the excitation spectra or the emission spectra or both Is there a good reference on this subject specifically :smile:
  45. fsonnichsen

    Maximum Fluorescence Energy vs Excitation

    I have taken a time dependent fluorescence series of spectra for an ethylene glycol solution using a 532nm laser as the excitation source. I have attached the spectra to this post. Nothing looks unusual-there is a sharp notch near the 532nm line--this is due to a filter I have used to protect...
  46. fsonnichsen

    Excitation Effects for Fluorescence Spectroscopy

    I have read from time to time (e.g. Lakowicz) that the fluorescence spectrum of a substance is not generally influenced by the wavelength excitation source. On the other had there is a correlation as exemplified in excitation-emission matrix spectra for example. The obvious case is for...
  47. R

    Finding Vibrational Spacing from Fluorescence and Absorption Spectre

    Homework Statement The fluorescence spectrum of anthracene vapor in the figure shows peaks with maxima at 440 nm, 410 nm, 390 nm, and 370 nm, whereas the absorption spectrum has peaks at 360 nm, 345 nm, 330 nm, and 305 nm. Assuming that only one vibrational mode contributes to these...
  48. K

    Physical Chemistry: Kinetics and fluorescence

    Homework Statement Consider fluorescence (light emission from an electronically excited state of a molecule) in the presence of a quenching molecule M. Quenching refers to the removal of energy from an excited electronic state by collision, and so without light emission. A mechanism for such...
  49. E

    What is the difference between Raman scattering and fluorescence

    What is the difference between Raman scattering and fluorescence emission?
  50. P

    Transitions using Fluorescence Spectroscopy

    Hi all! I'm doing undergrad research work using fluorescence spectroscopy on crystals. My adviser believes that we should be able to find new transitions via this method, but I'm rather unsure about how steady mental ground my adviser is sitting on, as he is very old. Right now I am...