Single-crystal ZnS1−xSexnanoribbons with various compositions were synthesized through an Au-catalyzed vapor transport method. Under two-photon pumping with an 800 nm femtosecond pulsed laser, the spontaneous emission peak of the ternary nanoribbons undergoes a gradual red-shift from 422 to 464 nm with the increase of Se content. When the pump energy densities are increased above the thresholds, the nanoribbons exhibit a tunable upconverted laser emission accompanied by a dramatic decrease in spectral linewidth as a set of sharp peaks on the corresponding wavelengths of each sample, featuring the occurrence of stimulated emission. Two components appear in the fluorescence lifetimes, which indicate that the ZnS1−xSexnanoribbons have two different recombination centers. Both lifetime components decrease with the increase of pump energy, further confirming the occurrence of stimulated emission. The two-photon pumped lasing behavior was also observed from single nanoribbons, in which the photoluminescence (PL) spectra are composed of multimode of lasing. The distinct modes show gain competition and pronounced shifts as a function of excitation density.
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