Phosphoroscope
Definition
A rotating chopper that alternately blocks the excitation beam and the detector. Fluorescence dies during the blocked window, phosphorescence persists, so only phosphorescence reaches the PMT.
- Function
- Separates phosphorescence from fluorescence
- Mechanism
- Rotating chopper alternately blocks excitation beam and detector
- Basis
- Fluorescence decays instantly; phosphorescence persists
- Output
- Only phosphorescence signal reaches the PMT
Common questions
Why is separating phosphorescence from fluorescence useful forensically?+
Some trace evidence, such as certain fibres, inks, or luminescent materials, has a distinct phosphorescence lifetime that helps discriminate between visually similar samples that would otherwise look identical under ordinary fluorescence viewing.
What happens to a sample's signal during the chopper's blocked window?+
When the chopper blocks the excitation beam, no new fluorescence is generated and any prompt fluorescence already emitted decays essentially instantly, so only the slower-decaying phosphorescence from the sample survives to reach the detector.
Could a modern time-resolved detector replace a mechanical phosphoroscope?+
Yes, pulsed light sources combined with gated or time-resolved detection achieve the same fluorescence-phosphorescence separation electronically, and many current instruments use that approach instead of a rotating mechanical chopper.
Related terms
- 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...
- 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,...
- Phosphorescence
- Light emission from the triplet excited state (T1) via a spin-forbidden radiative transition; characterised by emission persisting after the excitation source is...
- 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...
- Stokes Shift
- The wavelength difference between the excitation peak and the emission peak of a fluorophore. A positive Stokes shift (emission at longer wavelength...