Covers luminescence as light emitted without heat, from atoms or molecules relaxing after excitation. It sorts the phenomenon by excitation source, delay between excitation and emission (fluorescence versus phosphorescence), mechanism and whether excitation must be continuous. It then sets out Stokes' and Vavilov's laws for photoluminescence, fluorimetry, biochemiluminescence and medical and scientific applications.
Topic 33 of 42 in the MU Sofia syllabus for Physics (Medicine, Year 1). The free AceMed note covers it in 8 sections, about 309 words (2 min of reading), with 9 flashcards.
In this note
Luminescence
Definition
Types of Luminescence
Laws of Photoluminescence
Vavilov’s Law
Fluorimetry
Biochemiluminescence
Applications of Luminescence in Medicine & Science
Definition
Luminescence is the emission of light by a substance not caused by heat (in contrast to incandescence).
It results from atoms or molecules being excited by different processes and then emitting photons during relaxation to lower energy states.
Characterized by:
The excitation source (light, electric field, chemical reaction, radiation).
The emission mechanism (radiative or non-radiative transitions).
The delay between excitation and emission.
Types of Luminescence
1. By Excitation Source
Photoluminescence: excitation by photons (UV, visible light).
Electroluminescence: excitation by an electric field (used in LEDs, display panels).
Chemiluminescence: excitation from chemical reactions.
Radioluminescence: excitation by ionizing radiation (e.g., scintillators in nuclear physics).
2. By Delay Between Excitation & Emission
Fluorescence:
Very short-lived (10⁻⁹ to 10⁻⁶ s).
Emission stops immediately when excitation ceases.
Phosphorescence:
Delayed emission lasting microseconds → hours.
Due to forbidden electronic transitions (metastable states).
3. By Mechanism
Resonant Fluorescence: only radiative transitions back to ground state.
Indirect Luminescence: involves both radiative and non-radiative transitions.
Recombinant Luminescence: caused by recombination of charged particles (common in semiconductors).
4. By Nature
Spontaneous Luminescence: occurs without continuous external excitation.
Induced Luminescence: requires constant excitation to persist.
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