Semiconductor nanocrystals as phosphor alternatives for white LEDs

The fact that lighting represents a significant share of all globally consumed electrical energy (20%) drives the current transition from incandescent light bulbs to less energy-consuming alternatives such as solid state lighting. Their high efficiency (lm/W) and long lifetime make white light emitting diodes (LEDs) a viable alternative, especially when their light color and color rendering properties are optimized. Commercially available white LEDs typically consist of a blue LED chip in combination with rare-earth based phosphors, often YAG:Ce. Essential for a true breakthrough of white LEDs in daily life, is the emission of warm white light. This requires the addition of a red, often Eu-doped phosphor. However, their emission is relatively broad, stretching out to the near infrared. As we cannot see this part of their emitted light, energy loss is inherent to these materials. We propose the use of a versatile family of nanomaterials based on chalcopyrite Cu(In,Ga)(S,Se)2 nanocrystals as alternative phosphors for white LEDs, in combination with other Cd-free nanocrystals. This choice is based on the potential of Cu(In,Ga)(S,Se)2/ZnS nanocrystals with efficient, broad emission as white LED phosphor and the idea that the color temperature and color rendering properties can be improved by the addition of semiconductor nanocrystals with narrow, red emission or the combination with typical phosphors with green emission.