Anti-Stokes Fluorescence
Definition and meaning of Anti-Stokes Fluorescence in chemistry.
Anti-Stokes fluorescence is the emission of light from a molecule that has higher energy (shorter wavelength) than the light it absorbed. This occurs through multi-photon absorption, where a molecule absorbs multiple lower-energy photons simultaneously and emits a single higher-energy photon in return.
In more detail
Anti-Stokes fluorescence reverses the typical Stokes shift, where emitted photons normally have less energy than absorbed photons due to vibrational relaxation. In anti-Stokes processes, the molecule absorbs energy from two or more photons (often near-infrared) before emitting a single visible or ultraviolet photon. This is possible because the excited molecule can absorb additional photons before returning to the ground state. The process is valuable in biomedical imaging because near-infrared excitation penetrates tissue well while avoiding photodamage and background autofluorescence.
Key facts
| Field | Physical Chemistry |
|---|---|
| Process type | Multi-photon upconversion |
| Energy relationship | Emitted photon energy exceeds absorbed photon energy |
| Common excitation wavelength | Near-infrared (800–1000 nm) |
Erbium-doped fluoride nanocrystals (ErF3) excited with 980 nm infrared light emit visible green light at 550 nm, demonstrating anti-Stokes upconversion for deep tissue imaging and diagnostics.
Frequently asked questions
How does anti-Stokes fluorescence differ from regular Stokes fluorescence?
In Stokes fluorescence, a photon is absorbed and a lower-energy photon is emitted after the molecule relaxes vibrationally. Anti-Stokes fluorescence produces higher-energy emission by absorbing multiple photons before emission.
Why is anti-Stokes fluorescence useful in medical imaging?
Near-infrared excitation penetrates deep into biological tissue while producing visible or ultraviolet emission. This provides excellent spatial resolution, minimal background noise, and reduced photodamage to living cells.