LEDs are based on semiconductor materials. The transformation of energy into light is highly efficient and can produce different colors. However, it is not possible to generate white light directly from a semiconductor. White LED light can be created using various concepts. In industry, light is generated predominantly using the phosphor principle. Other concepts, for example the RGB principle in which white light is produced by combining red, green and blue LEDs, result in serious disadvantages, such as color shifts due to temperature and LED aging.
When the phosphor principle is used, a blue LED is combined with one or more lighting materials. A coated LED chip with a lighting material mixed in a matrix (e.g. silicone) emits white light. The matrix material contains small quantities of a fine lighting material distributed in the matrix, for example based on yttrium aluminum garnet (YAG) or alkaline earth orthosilicate (BOSE).
Not all energy states of charge carriers are possible in crystalline materials or lighting materials. For this reason, electronic bands or band structures, which define the energies that various charge carriers can and cannot have, are often referred to. Additional energy bands or states can also be generated in these band structures by incorporating foreign atoms (also called activators) in a targeted way. The basic operating principle of a lighting material is based on the physical principle of luminescence. Light is generated here through the excitation of an electron with the energy of the (blue) light which falls upon it. This transports the electron from a low energy state (valence band) to a higher energy state (generated by activators), or from the so called conduction band. This process also creates a hole in the valence band. After a certain period, the electron releases its energy by emitting light and returns to the valence band. The wavelength of the light generated in this way depends on the band structure of the material and the activators. For lighting materials used in the lighting industry, this is in the visible range.
isiphor® – high performance lighting materials from EMD Performance Materials
EMD Performance Materials develops these high performance lighting materials under the brand name isiphor®. The materials absorb blue light, are excited and emit white light. The quality and properties of the lighting material determine the intensity of the light and control the color temperature (CCT, correlated color temperature). The correlated color temperature describes the temperature of a white source of light. Increments of white range from cold and neutral to warm white. EMD Performance Materials' color-on-demand concept makes it possible to achieve the desired color of light depending on the composition of the lighting material and fulfill a wide range of customer requirements in a tailored solution. EMD Performance Materials' isiphor® high performance lighting materials are a crucial factor in utilizing the LED technology's huge potential in terms of light quality, energy savings and long life span. isiphor® lighting materials are suitable for applications in lighting and the display sector.
White light can also be generated using related concepts – for example using a (near) UV-LED combined with blue and yellow lighting materials (or a green-red combination). These lighting materials are optimized for a UV-LED source.
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