STATE COLLEGE, Pa., Dec. 5, 2017 — Researchers are closer to creating a tunable semiconductor diode laser from hybrid organic-inorganic perovskites. Using a material composed of an inorganic perovskite sublattice with relatively big organic molecules confined in the middle, a Penn State research team demonstrated that optically pumped continuous-wave lasing could be sustained for over an hour.
A red laser beam shines on a card bearing a replica of Penn State's academic logo. Courtesy of Yufei Jia/Penn State.
The next big step for this team is to switch from optical pumping with an external laser to a perovskite laser diode that can be powered directly with electrical current.
“The ultimate goal is to make an electrically driven perovskite laser diode,” said professor Chris Giebink. “That would be a game changer. It is fairly easy to make the perovskite material lase by optical pumping, that is, by shining another laser on it. However, this has only worked for very short pulses due to a poorly understood phenomenon we call lasing death.
“Getting it to go continuously is a key step toward an eventual electrically driven device. What we found in this recent study is a curious quirk. We can avoid lasing death entirely just by lowering the temperature of the material a little bit to induce a partial phase transition.”
When researchers brought the temperature below the phase transition, they found that the material initially emitted light from the low-temperature phase. But within 100 nanoseconds, the material changed over and began lasing from the high-temperature phase, and continued to do so for over an hour.
“It turned out that as the material heated up, although most of the material remained in the low-temperature phase, small pockets of the high-temperature phase formed, and that was where the lasing was coming from,” said researcher Yufei Jia.
Researchers noted that in the perovskite material, the arrangement of the high-temperature-phase inclusions inside the low-temperature bulk appeared to mimic inorganic semiconductor quantum wells. Since the intensity of lasing depends on how many charge carriers can be packed into quantum wells, researchers believe that the noted similarity to quantum wells in the perovskite material could play a role in enabling continuous lasing, and could serve as a model for engineering improved perovskite gain media.
“The jury is still out on this explanation,” Giebink said. “It may be something more subtle.”
Nevertheless, the results point toward an opportunity to engineer a material that has the built-in qualities of this mixed phase arrangement, but without having to actually cool the material to low temperature.
A flexible organic laser diode could be incorporated into form factors not possible for their inorganic counterparts. While inorganic semiconductor lasers are relatively limited in the wavelengths they emit, researchers could synthesize any wavelength in an organic laser by tailoring the structure of the organic molecules. This tunability could be useful in applications ranging from medical diagnostics to environmental sensing.
“If we can solve the electrical pumping problem, perovskite lasers could turn into a technology with real commercial value,” Giebink said.
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