Phosphorescence
Definition
Light emission from the triplet excited state (T1) via a spin-forbidden radiative transition; characterised by emission persisting after the excitation source is removed, with lifetimes from microseconds to minutes.
- Emission source
- Triplet excited state (T1)
- Lifetime range
- Microseconds to minutes
- Key physics
- Spin-forbidden radiative transition
Common questions
What's the difference between phosphorescence and fluorescence?+
Both emit light after absorbing energy, but phosphorescence comes from the triplet state and lasts much longer (milliseconds to minutes). Fluorescence comes from the singlet state and stops almost instantly when the light source turns off. Phosphorescence's long glow is because the spin flip makes the transition back to the ground state slower.
Why does phosphorescence keep glowing after the excitation source is removed?+
The electrons in the triplet state are in a spin-forbidden transition. This restriction slows down the radiative decay, so it takes milliseconds to seconds (or even minutes in some cases) for the light to come out. While you're still seeing that delayed emission, the external light is already gone.
How is phosphorescence useful in forensic work?+
Phosphorescent materials emit light persistently after excitation is removed. That delayed, long-lifetime emission can be detected under controlled lighting conditions, giving analysts time to observe and document the effect when examining luminescent evidence.
Related terms
- Jablonski Diagram
- An energy-level diagram showing the ground state, singlet excited states, and triplet state of a molecule, with arrows indicating absorption, internal conversion,...
- Stokes Shift
- The wavelength difference between the excitation peak and the emission peak of a fluorophore. A positive Stokes shift (emission at longer wavelength...
- Absorption
- The purification technique in which a crude antiserum is mixed with antigen preparations from cross-reacting species. Cross-reactive antibodies bind those antigens and...
- Beer-Lambert Law
- A = εbc. Absorbance equals molar absorptivity times path length times concentration. The linear relation between absorbance and concentration that makes UV-Vis...
- Chromophore
- The molecular subunit responsible for a dye's colour, typically a conjugated double-bond system; chemical erasure destroys the chromophore while leaving the decolourised...
- Fluorescence
- Light emission following absorption of light at a shorter (higher-energy) wavelength. Fluorescein absorbs blue-green excitation light and emits yellow-green light. The emitted...
- Fluorescence Lifetime
- The average time a fluorophore spends in the S1 excited state before emitting a fluorescence photon; typically 1-10 ns for organic fluorophores,...
- Fluorescence Quantum Yield (Phi)
- The fraction of absorbed photons that result in fluorescence emission (0 to 1); determines the brightness of a fluorescent signal and is...
- Kubelka-Munk Model
- A diffuse-reflectance theory relating the measured reflectance of a scattering-plus-absorbing layer to its absorption and scattering coefficients; used in forensic paint and...
- Molar Extinction Coefficient (ε)
- The intrinsic absorptivity of a molecule at a given wavelength, in L/(mol·cm); oxyhaemoglobin at 415 nm has ε ≈ 125,000, making it...
- Phosphoroscope
- A rotating chopper that alternately blocks the excitation beam and the detector. Fluorescence dies during the blocked window, phosphorescence persists, so only...
- Quantum Yield (Φ)
- Photons emitted divided by photons absorbed. A unit-less efficiency between 0 and 1. Quinine sulphate in 0.5 N sulphuric acid sits at...
Explained in these topics
- Fluorescence and Phosphorescence SpectroscopySpin-forbidden emission from the lowest excited triplet state T1 back to S0, with lifetimes of milliseconds to seconds because the spin flip slows the radiativ...
- Light-Matter Interaction: Absorption, Reflection, FluorescenceLight emission from the triplet excited state (T1) via a spin-forbidden radiative transition; characterised by emission persisting after the excitation source...