We found in our previous publication [1] in Fig. 2 (here Fig. 1) that the pump fluence unit labeling in Fig. 2 and the related expressions in the paper was incorrect. Here we provide a version of Fig. 2 and the corrected related expressions. It should be mentioned that the main results, techniques, and conclusions presented in the published paper [1] would not be affected.

 

Fig. 1. Optically pumped lasing features of a single ZnO MW, not covered and covered by AgNWs: (a) PL spectra of a single ZnO MW as a function of the pumping fluence varying in the range of 98.7–259.8 kW/cm². (b) PL spectra of the ZnO MW covered by AgNWs, as a function of the pumping fluence varying in the range of 95.8–187.7 kW/cm². (c) Comparison of the PL spectra of the single ZnO MW, not covered and covered by AgNWs, under a pumping fluence of 175.4 kW/cm². (d) Comparison of the integrated PL intensity of the single ZnO MW, not covered and covered by AgNWs, versus various pumping fluences.

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As described above, the as-synthesized single ZnO MW exhibits a well-defined geometry, especially for the hexagon-shaped cross-section. Whilst possessing superior optical gain characteristics, the hexagon-shaped ZnO MWs can be used for achieving photon amplification in these naturally formed WGM microresonators [31,38,44,52]. A single ZnO MW not covered, and covered by AgNWs, are optically pumped by a fs-pulsed laser, as described in the experimental procedures. Figure 2(a) (here Fig. 1(a)) shows the power-dependent excitation emission spectra of a single bare ZnO MW. Under low pump fluence excitation (for example, 98.7 kW/cm², the black solid curve in Fig. 2(a)), a broad spontaneous emission band, peaking at 391.6 nm, with a full width at half-maximum (FWHM) of λ_FWHM ∼ 12.5 nm (where λ_FWHM represents the wavelength) is obtained. When the pump fluence increases to 175.4 kW/cm², several sharp peaks with an average linewidth λ_FWHM of approximately 0.20 nm appear over the spontaneous emission band. The spectral linewidth of these sharp peaks is comparable to that reported for room-temperature hexagonal ZnO MWs, suggesting the occurrence of lasing action. Each emission peak corresponds to a single WGM microresonator [31,38,44]. The mode spacing between two neighboring peaks, that is, Δλ ∼ 0.46 nm, is nearly the same, which suggests that the sharp emission modes originate from the same waveguide. As the pump fluence is increased further, the PL intensity increases correspondingly.

By adding the AgNWs, the same MW was also optically pumped by a fs-pulsed laser (see details of the micro-PL measurement in the experimental procedures). Similarly, Fig. 2(b) (here Fig. 1(b)) shows the typical power-dependent PL spectra. As the pump fluence less than 136.4 kW/cm², the PL spectra were dominated by a group of spontaneous emission peaks. That is, the main PL peaks centered around 391.5 nm, and corresponding average FWHM of approximately 12.5 nm. When the pump fluence reaching 136.4 kW/cm², a series of sharp and evenly spaced peaks appear in the spontaneously emitted PL spectrum of the samples. Varying the pump fluence over 136.4 kW/cm², the PL spectra are dominated by a group of the sharp peaks. The appearance of these peaks indicates that the lasing action can also occur from the same ZnO MW, now covered by the AgNWs [31,38,44]. To further analyze the influence of the added AgNWs on the lasing performance of the single ZnO MW, a comparison of the lasing spectra of the same ZnO MW, under both bare as well as AgNW-covered conditions and same excitation power intensity of 175.4 kW/cm², is depicted in Fig. 2(c) (here Fig. 1(c)). We observed that an enhancement ratio—more than 15 times the lasing output intensity—was achieved by depositing the AgNWs on the ZnO MW [38,39,44,51]. In addition, the Q-factor of a single bare ZnO MW was calculated as approximately 2447, according to the formula Q =λ/Δλ, where λ is the lasing wavelength. By incorporating the AgNWs, a Q-factor of approximately 3918 is obtained, which is considerably higher than that of the bare MW-based WGM microcavity (or microresonator).

Further, to illustrate the optically pumped lasing action of the wires, the integrated PL emission intensity of the single ZnO MW, not covered and covered by AgNWs, as a function of the pumping fluence is shown in Fig. 2(d) (here Fig. 1(d)). These results imply that a single MW covered by the AgNWs yields a more efficient output than a bare MW. In particular, the lasing threshold (P_th) of a single ZnO MW was estimated to be approximately 171.4 kW/cm², which is much higher than P_th = 135.1 kW/cm² of the same MW covered by the AgNWs. For the AgNW-coated ZnO MW, significant improvement of the WGM lasing characteristics, including the observed enhancement of lasing output, a lower threshold and an improved performance optical microresonator, can be achieved. This improves the external luminous efficiency of a single ZnO MW having a hexagonal cross-section [36,38,39]. As the primary PL peak of the single ZnO MW matches well with the localized surface plasmon resonance of the AgNWs, the PL emissions of the AgNW covered ZnO MW is enhanced. Therefore, the excitation of the ultraviolet plasmons of AgNWs can open new avenues to achieve enhanced WGM lasing characteristics of single ZnO MWs having hexagonal cross-sections [36,38,39].