Toward single-mode random lasing within a submicrometre-sized spherical ZnO particle film

Ryo Niyuki,Hideki Fujiwara,Naoto Koshizaki,Keiji Sasaki,Yoshie Ishikawa,Takeshi Tsuji

doi:10.1088/2040-8978/18/3/035202

Abstract

We had recently reported unique random laser action such as quasi-single-mode and low-threshold lasing from a submicrometre-sized spherical ZnO nanoparticle film with polymer particles as defects. The present study demonstrates a novel approach to realize single-mode random lasing by adjusting the sizes of the defect particles. From the dependence of random lasing properties on defect size, we find that the average number of lasing peaks can be modified by the defect size, while other lasing properties such as lasing wavelengths and thresholds remain unchanged. These results suggest that lasing wavelengths and thresholds are determined by the resonant properties of the surrounding scatterers, while the defect size stochastically determines the number of lasing peaks. Therefore, if we optimize the sizes of the defects and scatterers, we can intentionally induce single-mode lasing even in a random structure (Fujiwara et al 2013 Appl. Phys. Lett. 102 061110).

Highlights

Introduction domainsAmong several approaches for controlling random lasing modes [12,13,14,15,16,17,18,19,20], we numerically and experimentally proposed a singular structure [21,22,23,24,25] composed of monodispersive scatterers and defect regions
To improve the controllability, especially, to clarify the roles of defect particles and the origins why the single mode lasing occurred in our proposed random lasers, we experimentally studied the dependence of random lasing properties on defect size in a structure of mono-dispersive spherical ZnO nanoparticles with polymer nanoparticles acting as the defects
Regardless of the defect size, a few discrete sharp lasing peaks were observed at each defect, and their characteristics were clearly different from those observed for typical random lasers

Summary

Experiment

We used quasi-mono-dispersive ZnO nanoparticles as scatterers and gain materials. In figure 2(d), the emission spectra at defect-free sites have multiple sharp peaks superposed on a collapsed broad emission spectrum, similar to those for typical random obtained (figure 1(a)); these were almost mono-dispersive and spherical, in contrast to the commercially available, irregularly shaped poly-dispersive ZnO nanoparticles. After dispersing these ZnO nanoparticles in water, we added commercially available green fluorescent polystyrene nanoparticles with diameters of 300, 900 and 2000 nm into the solution as point defects. After confirming the locations of the defects, we measured the emission spectra by changing the excitation intensity

Result and discussion

Conclusion