Research Projects

Among the commercially available LEDs, blue LEDs in the range 450-470 nm are most efficient. The first application of the blue LED was for solid state lighting. Due to huge demand all over the world, these LEDs are produced in large quantities. As such, the technology is developed and the cost has come down. During this early period, the emphasis was to obtain most energy efficient method to convert electrical energy into visible light. With YAG:Ce yellow phosphor and blue LED, this goal could be easily accomplished. The resulting phosphor converted LED (pc-LED) lamps have now attained the light output in excess of 140 lm/W. Apart from the conversion efficiency, other figures of merit such as colour rendition index (CRI), correlated colour temperature (CCT), etc. for the new solid-state lighting (SSL) were also compared with the objectives set by the earlier technologies. For attaining good CRI, phosphor converted LED was quite inadequate as it cannot provide CRI better than 70, although it is most energy efficient. Making compromise on energy conversion efficiency, LED lamps with high CRI could be developed using blend of green and red phosphors (2- phosphor converted LED). A scheme to obtain greater CRI by addition of yellow phosphor (3- phosphor converted LED) had also been proposed. LED lamps commonly available in India are produced with 465 nm blue chip and Yttrium aluminum garnet, Y3Al5O12:Ce (YAG:Ce) phosphor. YAG:Ce phosphor is mostly imported from China. We are depending on China for lanthanides and Yttrium at Industrial level. In light of the recent political developments, it is advisable to break away from dependence on China. It is thus proposed to develop Lanthanide free phosphors for solid-state lighting applications. These phosphors will function as import substitute for the Chinese materials.