Introduction
Summary
- The notes elaborate on the various types of luminescence categorized by excitation sources, emission delay, mechanisms, and nature, highlighting forms such as photoluminescence, electroluminescence, and chemiluminescence. They delve into the scientific laws of Stokes and Vavilov, which dictate the behavior and efficiency of photoluminescence. Additionally, the notes cover fluorimetry and bio chemiluminescence, explaining their operational principles, applications, and significance in scientific research and medical diagnostics.
Types of Luminescence
- Luminescence: Emission of light by substances not resulting from heat.
- Categories:
- By Excitation Source:
- Photoluminescence: Excitation by light.
- Electroluminescence: Excitation through an electric field.
- Chemiluminescence: Excitation via chemical reactions.
- Radioluminescence: Excitation by ionizing radiation.
- By Delay Between Excitation and Emission:
- Fluorescence: Instantaneous emission, lasting nanoseconds to microseconds.
- Phosphorescence: Delayed emission, lasting from microseconds to several hours.
- By Mechanism:
- Resonant Fluorescence: Only radiative transitions to the ground state.
- Indirect Luminescence: Both radiative and non-radiative transitions.
- By Nature of Luminescence:
- Spontaneous Luminescence: Occurs without continuous external excitation.
- Induced Luminescence: Requires continuous external excitation.
- Recombinant Luminescence: Due to recombination of charged particles.
Laws of Stokes and Vavilov in Photoluminescence
- Stokes' Law:
- Principle: Emitted light typically has a longer wavelength than absorbed light.
- Formula: hν = W + Q
- Energy terms represent absorbed photon energy, emitted photon energy, and energy lost to non-radiative processes.
- Vavilov's Law:
- Principle: The quantum yield of photoluminescence remains constant under unchanged conditions.
- Formula: n(q) = N*/N = constant
- Defines quantum yield as the ratio of emitted to absorbed photons.
Fluorimetry and Biochemiluminescence
- Fluorimetry:
- Description: Measures the intensity of fluorescence emitted after light excitation.
- Operational Principle: Uses a monochromator for excitation and a spectral device for measuring fluorescence.
- Formula: IF = n(a) · I0 · ε(v) · c · d
- Elements include quantum yield, intensity of exciting light, molar extinction coefficient, sample concentration, and cuvette path length.
- Biochemiluminescence:
- Description: Luminescence from biochemical reactions, often enzyme-driven (e.g., luciferase).
- Applications: Essential in medical diagnostics and research for biomolecule detection and quantification.