The creation of cheap alternatives to fluorescent lighting tubes is keeping an army of researchers busy Most approaches so far mix red, green and blue light emitted from semiconductor materials to produce white light. But attempts at finding an efficient way to generate white light have met with varying degrees of success.
At Sandia National Laboratories, USA, a research team led by Lauren Rohwer has taken a completely different approach by using quantum dots to create the first solid-state white light emitting device. The efficiency achieved by the group was increased from 10-20% to 60%. The breakthrough was achieved by introducing a new encapsulation process that attaches quantum dots to the backbone of the encapsulation polymer, meaning that the dots are close but do not touch. Previous attempts have resulted in clumping of the dots, which causes them to lose their light emitting properties.
Quantum dots must be encapsulated to be used in lighting, and epoxy or silicon is usually used. Other researchers have achieved high efficiencies with quantum dots, but in an unencapsulated state (50% efficiency in dilute solutions).
‘Doing this we had to take care not to alter the surface chemistry of the quantum dots in transition from solvent to encapsulant,’ said Steven Thoma, who worked on the encapsulation part of the project.
During the next year the researchers will work on enhancing the light output by increasing the concentration of the quantum dots in the encapsulant. This will also serve to extend the understanding of quantum dot electronic interactions at high concentrations. ‘Highly efficient, low-cost quantum dot-based lighting would represent a revolution in lighting technology through nanoscience,’ said Rohwer.