Color Conversion Materials
A color conversion material is a term often used to describe phosphors, quantum dots, and other luminescent, fluorescent, or phosphorescent materials. Color conversion works when a material absorbs energy at certain wavelengths and then re-emits some of the absorbed energy at a different color or wavelength. This is different from color filtering where some of the optical energy (or colors) are only absorbed but not converted. In color filtering, the undesired light colors are removed from the spectrum and the absorbed light energy is converted into heat instead of light. Color filtering only works if the source of the original light contains the wavelength colors of interest. For example, a white light source can be filtered into red, green, and blue (RGB) since white color is made up of all the visible colors in a rainbow. However, a blue light cannot be filtered to produce green, red, or even white. A blue light can be converted to RGB and white (RGBW) using a color conversion material such as a phosphor.
Blue, violet, and ultraviolet light are made of photons with higher energy compared to green, yellow, red, and infrared light. High energy light can be efficiently converted to lower energy light. This is called down-conversion. Converting a lower energy light to a higher energy light (up-conversion) is more difficult but not impossible. Up-conversion generally requires two lower energy photons in order to produce a single higher energy photon. For example, two lower energy infrared photons at 1000 nm wavelength can, in principle, be converted to a single higher energy photon emitting in the green/cyan spectral region around 500nm. Up-conversion phosphors do exist but are generally less efficient compared to down-conversion phosphors.
Color conversion materials are widely used in lighting, imaging, and display technologies. Virtually every modern light source including white LEDs, backlight, or electronic display currently employ phosphors as the primary color conversion materials for color tuning.
Difference between color conversion and color filtering