The use of a material development method known as high-throughput experimentation (HTE), which allows for the screening of large composition areas of complex material systems, has led to the discovery of a dark red luminescent material for light-emitting diodes (LEDs). The new luminescent material can be used, for example, for warm-toned white LEDs for general lighting, for backlighting of liquid crystal display (LCD) screens, and for automotive applications.
LEDs save energy, have a long service life, and can be flexibly used in applications. However, the selection of colors for LEDs is still limited. To convert the ultraviolet or blue light of common semiconductor chip LEDs to white light or other colors, fluorescent materials – or luminescent materials – must therefore be placed on the semiconductor chip. These phosphors can cover a wide range of the color spectrum, but there are no efficient, stable phosphors that emit dark red light. Small differences in the composition of a luminescent material have huge influence on its emission properties. Therefore it is necessary to vary the composition of the material in small steps. This leads to a lot of samples which can not be produced or analyzed by hand.
A special HTE technology was developed to achieve this. It permits automated experiment planning as well as the establishment, characterization, and evaluation of so-called material libraries, which typically contain around 100 individual samples. In the HTE experiments, over 660 sample variants from twelve different material combinations were analyzed over a period of a few months to determine emission wavelength, light intensity, and structural phases.
The new, dark red-emitting luminescent material belongs to the large compound class of oxynitrides that permits a wavelength shift of up to 30 nm into the dark red range. The search for innovative luminescent materials is ongoing, as new material systems are consistently being screened.
This work was done by researchers at Siemens and Osram. For more information visit Siemens at http://info.hotims.com/40429-142 and Osram at http://info.hotims.com/40429-143 .