Valerie C. CoffeyA white-light laser has the potential to replace white LEDs in lighting, displays, sensing and telecom, with higher energy conversion efficiencies and higher output powers. But multicolor lasing from a small, monolithic semiconductor-based laser has remained elusive due to fundamental challenges in materials and structures.
Researchers at the Arizona State University (ASU; Tempe, Arizona, USA) have reportedly overcome these challenges for the first time, to create a multi-segment monolithic white laser that emits at one or all of the visible colors of the spectrum at once (Nat. Nanotech., doi:10.1038/nnano.2015.149). ASU professor Zheng Ning and colleagues worked with various nanomaterials in multiple configurations for more than ten years before successfully finding the solution. Lasing in green and red from a monolithic semiconductor sheet came first; but growing blue-emitting materials on the same sheet took two years to perfect.
The winning technique involved dynamically manipulating a ZnCdSSe alloy nanosheet along an axial temperature gradient during chemical vapor deposition growth. The team achieved the desired segmented nanosheet morphology separately from the desired material composition, a novel approach requiring multiple steps and simultaneous cation-anion exchange in a careful sequence. The resulting structures measure 60 by 45 µm and range in thickness from 60 to 350 nm.
The multi-segment monolithic nanosheets lase at red, green and blue wavelengths, and every color in between, when excited by a 355-nm pulsed laser at room temperature. The emission reaches across 190 nm of the visible wavelength range, the largest ever reported for such a structure.
The team’s experimental proof of concept will require further efforts to operate via battery instead of optical pumping. Still, the researchers believe that demonstration of the required growth process marks a significant step toward the goal of electrically operated white lasers.[Correction, 2015/08/07: We have changed the title of this story; the previous title incorrectly suggested that this development represented the first white laser rather than the first monolithic white laser.]