Questions tagged [fluorescence]

For questions relating to the radiation emitted by substances as a result of incident radiation.

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34 views

Which commonly available UV light source to use with fluorescein

I want to start experimenting with fluorescein. I have a 353 nm UV light source, but am thinking that it might be too short since it looks like peak excitation occurs at 494 nm. So am I correct in ...
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5answers
550 views

Why do different substances containing saturated hydrocarbons burns with different flame?

LPG and Candle wax both contain saturated hydrocarbon, yet LPG gives a clean white flame but a candle gives yellow flame with lots of smoke. Why so? I have read some answers on web which says that it ...
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Help with Forster distance conversion for FRET

For my project on Fluorescence, I'm trying to simplify the equation for the Forster distance (I obtained this from the Lakowicz book). To keep track, the units are in square brackets. $$R_0 = \left(\...
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24 views

How to proceed pyrene fluorescence probe for CMC determination?

Pyrene fluorescent probe is the most common method to determine the critical micelles concentration in researches. However, there is no obvious protocol for that method. Please I need a guidance from ...
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21 views

Why does the emission of dansyl group diminish with time in this experiment?

I don't know how to make sense of this. I what is happening when an enzyme (carboxypeptidase, which contains tryptophan as its only chromophore and uses a Zn(II) ion in its active center) hydrolises a ...
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105 views

Fluorometer for measuring fluorescence in a sheet of water

Does anyone know of a fluorometer that I could use to measure fluorescence in a thin sheet of water. So it would be like holding a piece of writing or printer paper vertically and trying to get a ...
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2answers
70 views

Implications of the excitation spectra

The fluorescence excitation spectra show the change in fluorescence intensity as a function of the wavelength of the excitation light. I'm interested in the certain physical implications of the above. ...
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1answer
116 views

Absorption and Emission at same wavelength?

Is it possible for a molecule to absorb and emit at the same wavelength? What is the reason behind it? I’m working on charged Tin porphyrins and got the excitation and emission (fluorescence) ...
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79 views

Data analysis in TCSPC for fluorescene decay (reconvolution with measured IRF)

I am trying to understand the data analysis of fluorescence decay counts measured by TCSPC technique, particularly with reconvolution with measured IRF. I am able to get the fitted counts (given by ...
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43 views

Chemical Potential in the Fluorescent Molecule

I'm reading this paper, which states that the chemical potential $\mu$ is determined by the steady-state balance of up and down transitions in a fluorescent molecule. I am happy with this ...
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71 views

Common chemcials that produce phosphorescence

Are there any common lab chemicals or household stuff that produce phosphorescence? I am aware of ZnS, CaS, Fluorescein, Erythrosin B, Vanillin Benzaldehyde, Vitamin B2, Tryptophan etc. I just need ...
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1answer
71 views

Is the XRF spectroscopy equally sensitive for every element?

I am curious whether or not every element can be equally well detected by using X-Ray-fluorescence-spectroscopy. Might there be any contitions or circumstances that make it hard/impossible to detect a ...
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2answers
109 views

Why do some molecules show non-symmetric absorption and emission bands?

I'm looking at a molecule of [Ru(bpy)3]2+ in water and the absorption and emission bands are not symmetrical. I want to know why the mirror image rule doesn't apply here. Is this because of the MLCT, ...
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1answer
124 views

Nitrogen dioxide fluorescence quenching and lifetime

Nitrogen dioxide fluorescence quenching: $$ \begin{align} \ce{NO2 + h\nu &->[$\varphi_\mathrm{Ia}$] NO2^{\ast}}\tag{I}\\ \ce{NO2^{\ast} &->[$k_2$] NO2 + h\nu'}\tag{II}\\ \ce{NO2^{\ast} +...
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1answer
56 views

Are there any fluorophores with lifetimes in the micro to milli second range?

I'm looking for a fluorophore with exceptionally long lifetime to use in an oxygen optode (the longer the lifetime the less timing precision needed in the electronics). So far the longest I have ...
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1answer
70 views

Deriving fluorescence intensity equations

I've been having trouble with deriving the equations in the following problem. The interaction between DNA and AO to form the AO–DNA complex can be expressed by the following reaction: $$\ce{...
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1answer
98 views

Latent blood detection with fluorescein

I need help with the reaction between fluorescein and blood in the method of detecting latent blood stains. I find it hard to find any literature on this subject. As far as I am concerned, the ...
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19 views

When an electron is excited to a singlet state, must it flip its spin state to enter the triplet state and flip once more to the ground state?

I understand the Jablonski diagram in that it has intersystem crossing from the singlet state to the triplet state, but how many spin switches are necessary to complete to phosphores? When an electron ...
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87 views

Is the activation energy always inversely proportional to the reaction rate?

When I obtained the activation energy using the Arrhenius equation for a 10-minute glowstick (rapid, rigorous reaction), it was almost 4 times that of a 12-hour glowstick (slow, mild reaction). ...
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1answer
83 views

Why has nature evolved to put a porphyrin (i.e. chlorophyll) as the chromophore in a leaf? [closed]

I'm stumped by this question: Why has nature evolved to put a porphyrin (i.e. chlorophyll) as the chromophore in a leaf? I've thought that it might have something to do with how sun emits light ...
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1answer
165 views

How to calculate molecular emission spectra?

Is there free software that can calculate the fluorescence emission spectra of organic molecules? Let's say, for example, rubrene There is a bunch of quantum free quantum chemistry software: https://...
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53 views

Does something like a fluorescent foil or a fluorescent film exist?

During my experiments I want the emitted laser beams to come back with a different wavelength than the original wavelength using a fluorescent foil or fluorescent film. The laser I'm currently using ...
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1answer
264 views

Why are most glow-in-the-dark things green?

I've noticed that many glow-in-the-dark objects you can purchase in the store are green. Occasionally I would come across something that was orange or blue, but mostly it seems that green is the ...
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273 views

Why do glow-in-the-dark substances dim gradually?

Related: How do things glow in the dark? Growing up, I had glow-in-the-dark stars on my ceiling and after being "charged" by having my lights on, they would phosphoresce for quite some time. However,...
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2answers
87 views

Measuring a high Michaelis constant using fluorescence

We have the task of measuring kinetic parameters of an oxidase reaction that has a $K_M$ of about $2 \,\text{mM}$. For that, we want to use a fluorescence assay based on Amplex Red. The latter is a ...
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Choosing the right wavelength for calibration curve and for analysis of actual results

Introduction: I am currently conducting a series of experiments in which I am studying the transport of polystyrene nanoparticles (PNPs) through sand and soil. This is done in sand/soil columns, into ...
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58 views

What's causing this dip in the FCS curve?

This is a fluorescence correlation spectroscopy measurement of light harvesting complexes. What could be causing the dip at 100 microseconds? Edit: The same thing was observed using fluorescence ...
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2answers
170 views

What fluorescent materials absorb visible light and emit UVC light?

What fluorescent materials, if any, exhibit anti-stokes shift such that they absorb visible light and emit ultraviolet light in the range of 250-285 nm? I'm interested in particular in materials that ...
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1answer
510 views

Is Beer-Lambert law also valid for fluorescence and luminescence?

When I measure optical density in a microplate reader the absorbance is proportional to the concentration and the height of the liquid. Is Beer-Lambert law also valid for fluorescence and luminescence?...
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1answer
78 views

What is the relationship between emission and fluorescence?

A molecule exposed to a photon with some energy is put into an excited state, and emits a photon of some energy when it returns to ground state. The photon that provided the energy for excitation ...
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3answers
83 views

Self tan mousse cannot contain UV, right?

So, I bought this self tanner specificly to avoid UV radiation. Back home I noticed that the bottle says it contains ultra violet: "The inclusion of Ultra Violet fluorescence in the base colour" . I ...
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1answer
35 views

How does light emission depend on temperature by fluorescence?

I have a glass, which emits green light after charging it with sunlight. I though this is fluorescence, and only photons with shorter wave length (than the green light has) can excite the electrons of ...
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1answer
155 views

Why does aqeous fluorescein shine when exposed to UV light?

I know that (aq) fluorescein "absorbs" UV light and releases light in the visible spectrum , but how does it do that. It is a really interesting and useful organic chemical and I just wanted to know ...
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1answer
266 views

Are there any (simple) molecules with very different absorption and emission dipole directions?

When a single molecule absorbs or emits light, it does so perpendicular to the direction of the respective transition dipole. In principle, the directions of the dipoles for absorption and emission ...
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90 views

Is it right to say that fluorescent lamps are actually fluorescent?

Fluorescence occurs rapidly ($\approx 10^{-6}$ to $10^{-9}$ s) but phosphorescence is slow, and is therefore observable ($> 10^{-4}$ s). So, is it right to say that fluorescent lamps actually ...
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2answers
813 views

What is the exact relationship between the Pi conjugated bonds in organic molecules and fluoroscence of those molecules?

Some compounds are more fluorescent than others, and some of those are Rhodamine, Phenolphtalin, naphthalene, anthracene etc. I want to know why these exact molecules undergo such phenomena, what is ...
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1answer
158 views

Calcium detection using XRF

I have a mixture of metal oxides in powder form. Mainly Iron oxide, silicon dioxide, and calcium oxide. I know for certain calcium oxide is in the mixture, but my handheld XRF is not detecting it. I ...
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35 views

Does the laser side of laser fluorescence spectroscopy have to be so complicated?

I understand the working principle behind zapping some gas and looking at spectral emissions, and I can see why photodetection is so difficult. But I thought that pointing a laser into a vacuum ...
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1answer
1k views

What makes scorpions glow under UV light?

What substance (or class of substances) is responsible for the neon blue-colored fluorescence we observe when we shine UV light on scorpions? Do note, I want to know what substance makes them glow ...
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39 views

Is there any molecule describable by three-level with mixed parity and transition dipole moments in different directions?

I would like to know if there are molecules described by a three-level system with mixed parity and transition dipole moments in different directions. By mixed parity I mean all three transitions can ...
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2answers
97 views

Is this online fluorophore database reliable?

I need fluorescence spectra for various fluorophores in certain dispersion media for some calculations. There is an online database of University of Arizona: http://www.spectra.arizona.edu/ Is using ...
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3answers
722 views

What are the requirements for FRET?

I have a question about fluorescence resonance energy transfer (FRET), and the requirements needed for this technique. Q: Which of the following need to be met for FRET? A) Strong overlap between ...
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2answers
908 views

What is special about the molecule luciferin that it can emit light?

A classic example of bioluminescence; the protein luciferin is oxidized by the enzyme luciferase, releasing energy as light. What is it that gives luciferin this ability? Why can't just about any ...
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2answers
78 views

Is there a chemical which fluoresces only after coming in contact with water? [closed]

I require an easily available chemical compound which in its pure form, does not fluoresce under UV light. However upon coming in contact with water (at room temperature) it fluoresces under UV light....
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1answer
403 views

Why do fluorescence intensities decline with replicate number?

I am performing a determination of riboflavin with fluorescence spectrophotometry. I've dissolved my riboflavin in a dilute GAA solution, created a calibration curve and measured my unknown's ...
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1answer
117 views

Thermochromic, fluorescent fluid

I'm a total layman in chemistry and am working on an interactive sculpture project and therefore am researching into fluids that have certain properties - long story short: we are thinking on having a ...
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1answer
153 views

Compound with a bright green emission when electrically excited

I rolled back the edit because I really am looking for the following: I am looking for an element or compound that would have a bright green emission when electrically excited and is a gas at between ...
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2answers
1k views

What makes a species “fluorescence quencher”?

I just came across an article where they said that sodium fluoride is not quencher (in the context of fluorescence). Why is NaF not a quencher but NaBr is one?
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5k views

What should the Rehm-Weller equation look like?

The Rehm-Weller equation, which defines the energy change for photoinduced electron transfer according to Lakowicz "Principles of Fluorescence Spectroscopy" [1, p. 337] should look like: $$\...
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1answer
163 views

Interpretation of Figure - biofunctionalization

In this paper on page 1985 they say: Fluorescence analysis confirmed that enhanced protein binding at higher electron dose depends only to a small extent on the slight increase in the lateral ...