The total absence of any heat; -273o
C, 0 Kelvin.
A small amount of an element added to a very pure chemical to bestow luminescent properties.
The emission of light from a phosphor after the excitation has ceased.
α Particle. These are Helium nuclei (two neutrons plus two protons). They are a product of radioactivity but only penetrate a few centimetres in air due to their high charge.
A luminescent process that does not obey Stokes’ law, i.e. the excitation wavelength is longer than the emission wavelength.
β Particle. A high-energy electron created when a neutron turns into a proton within a radioactive nucleus; it is negatively charged.
Another term for Beta particles.
Long UV (UV-A) from a very dark blue glass tube or bulb (Wood’s glass).
A theoretical material that will emit radiation according to Planck’s equation, i.e. the emission spectrum depends only on the temperature of the material. The colour of the emission moves from infrared through red, orange, white and blue-white as temperature increases.
Black Body Curve
A curve on the chromaticity diagram describing how the colour point of black body radiation will change with temperature (given in Kelvin).
The natural colour of a material in daylight.
The symbol for the speed of light in a vacuum. ~ 3×108
Charge-Coupled Device; an array of light-sensitive electronic detectors.
The SI unit of luminous intensity that is roughly equal to the light given off by a candle.
The property of a particle governing how much it is affected by an electromagnetic field. Ions will have a positive or negative charge.
The addition of an extra ion, which enables an activator ion to enter a crystal lattice when it does not have the correct charge, e.g. Cu+
A chart that permits the definition of colours using x and y coordinates.
Commission Internationale d’Eclairage. 1931. An international body that standardised the definition of colour in 1931. It uses x, y coordinates on a chromaticity diagram.
The point on a chromaticity diagram that matches a specific colour and defined by its x, y coordinates.
The ability of a light source to accurately reflect the colours of an object.
Colour Rendering Index
A scale of colour rendering ability; 100% is perfect colour rendering. Tri-chromatic phosphor lamps achieve about 85% CRI.
The definition of near white colours using the Kelvin scale. E.g. 3000 K warm white, 3500 K white and 4500 K daylight.
The incorporation of an activator into a host by precipitating them simultaneously from a mixed solution.
Cathode Ray Tube. A device used to generate and guide a beam of electrons onto a screen coated with a phosphor.
Crystal Field Effect
The effect of the surrounding crystal lattice on the activator of a phosphor. Substitution with similar ions can cause subtle changes or shifts on emissions. e.g. Mg, Ca, Sr, Ba.