A “freshman-chemistry-level” technique for growing nanowires produces tunable lasers that are nearly 100 percent efficient. With low lasing thresholds and Q factors around 3600, these single-crystal lead halide perovskite nanowires could be suitable for miniature optoelectronic devices. “While most researchers make these perovskite compounds into thin films for the fabrication of solar cells, we have developed an extremely simple method to grow them into elongated crystals that make extremely promising lasers,” said Song Jin, professor of chemistry at the University of Wisconsin-Madison. Unsorted nanowire crystals immediately after production. Courtesy of Song Jin, University of Wisconsin-Madison. The new growth technique skips the costly, complicated equipment needed to make conventional lasers, Jin said. The nanowires grow in about 20 hours once a glass plate coated with a solid reactant is submerged in a solution of a second reactant. Simple changes to the recipe can produce nanowires with different emission wavelengths in the visible spectrum. “The single-crystal perovskite nanowires grown from solutions at room temperature are high quality, almost free of defects, and they have the nice reflective parallel facets that a laser needs,” Jin said. “Most importantly, according to the conventional measures of lasing quality and efficiency, they are real standouts.” Before these nanowire lasers can be used in practical applications, Jin said, their chemical stability must be improved. It will also be important to find a way to cause lasing with electricity rather than with optical pumping, as has been done so far. Funding came from the U.S. Department of Energy Basic Energy Sciences program. The research was published in Nature Materials (doi: 10.1038/nmat4271). For more information, visit www.wisc.edu.