This document discusses different types of photoluminescence including fluorescence, phosphorescence, and phosphor thermometry. Fluorescence involves light emission from a substance that has absorbed light or electromagnetic radiation at a higher energy level, and re-emits light at a lower energy level. Phosphorescence differs in that the re-emission of light occurs over longer time scales from "forbidden" energy state transitions. Phosphor thermometry uses characteristics of phosphor luminescence emissions like brightness or color that change with temperature for temperature measurement applications. Common phosphors used include zinc sulfide doped with copper or rare earth doped aluminosilicates.

2. INTODUCTION
Photoluminescence(abbreviated as PL) is light
emission from any form of matter after the absorption of
photons (electromagnetic radiation).
It is one of many forms of luminescence (light
emission) and is initiated by photo excitation (excitation
by photons).
Time periods between absorption and emission may
vary: ranging from short femtosecond-regime for
emission involving free-carrier plasma in inorganic
semiconductors up to milliseconds for phosphorescent
processes in molecular systems; and under special
circumstances delay of emission may even span to
minutes or hours.

3. Resonance fluorescence
• Resonant excitation describes a situation in which photons of a
particular wavelength are absorbed and equivalent photons are very
rapidly re-emitted.
• in the gas phase, this process involves electrons but no significant
internal energy transitions involving molecular features of the
chemical substance between absorption and emission
Semi-conductors
• In crystalline inorganic semiconductors where an electronic band structure is
formed, secondary emission can be more complicated as events may contain
both coherent such as resonant Rayleigh scattering where a fixed phase
relation with the driving light field is maintained (i.e. energetically elastic
processes where no losses are involved) and incoherent contributions (or
inelastic modes where some energy channels into an auxiliary loss mode).
Forms of Photo Luminescence

4. Fluorescence
 The emission of light by a
substance that has absorbed light
or other electromagnetic radiation.
It is a form of luminescence.
 The emitted light has a
longer wavelength, and therefore
lower energy, than the absorbed
radiation. The most striking
example of fluorescence occurs
when the absorbed radiation is in
the ultraviolet region of the
spectrum, and thus invisible to the
human eye, while the emitted light
is in the visible region, which
gives the fluorescent substance a
distinct color that can only be seen
when exposed to UV light.
Fluorescent minerals emit visible light when
exposed to ultraviolet light
Bio fluorescent marine organisms

5. Phosphorescence
 Phosphorescence is a specific type
of photoluminescence related
to fluorescence. Unlike fluorescence, a
phosphorescent material does not
immediately re-emit the radiation it
absorbs.
 The slower time scales of the re-emission
are associated with "forbidden" energy
state transitions in quantum mechanics.
As these transitions occur very slowly in
certain materials, absorbed radiation
may be re-emitted at a lower intensity for
up to several hours after the original
excitation.
 Commonly seen examples of
phosphorescent materials are the glow-in-
the-dark toys, paint, and clock dials that
glow for some time after being charged with
a bright light such as in any normal reading
or room light. Typically the glowing then
slowly fades out within minutes to up to a
few hours in a dark room.
phosphorescen
t pigment blue
in the dark
phosphorescen
t pigment blue
(alkaline earth
metal silicate )
Phosphorescent bird figure

6. Phosphor thermometry
Phosphor thermometry is
an optical method for surface
temperature measurement. The
method exploits luminescence emitted
by phosphor material. Phosphors are
fine white or pastel-colored inorganic
powders which may be stimulated by
any of a variety of means to luminance,
i.e. emit light. Certain characteristics of
the emitted light change with
temperature, including brightness,
color, and afterglow duration. The latter
is most commonly used for temperature
measurement.

7. ZNS:Cu
Rare Earth doped Alumina silicates.
Ex.SrAlO4:Eu,Dy CaAlO4:Eu,Dy
Fullerene-doped polymers.
Fullerene-doped inorganic materials.