What is Luminescence?
The property of emission of light when a energetic particle
impinges on material
(semiconductors) leading to creation of
electron hole pairs and excitation of carriers. When these carriers come to
their equilibrium states they emit light.
Mechanism of Recombination
Radiative
Recombination
When the excited
excess carriers reach equilibrium positions by emission of photons it is said
to be Radiative recombination
Non-Radiative
Recombination
When the excited excess carriers reach equilibrium positions
by emission of phonons due to surface / bulk defects / other defects it is said
to be non-radiative recombination.
What Is Activator?
Impurity atom
occurring in relatively small concentrations in host material or a small
stoichometric excess of one of constituents of material which exhibits the
property of Luminescence.
What Is Killer?
Presence of certain
type of impurity may also inhibit Luminescence of other centers, in which case
they are referred as killers.
After a particular level of concentration, the efficiency
decreases as excess carrier returns to the ground state only if there is no
other activator with in a sphere of
Dependence of luminescence efficiency on Activator
concentration
CHARACTERISTICS OF A
PHOSPHOR
- High concentration of carrier traps.
- High emission efficiency.
- Large trap depth.
- Traps, Luminescence & lattice are not to be damaged by repeated irradiation & heating process.