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23 Feb 2016 Scientists in NUS have developed a very low threshold, multi-photon pumped laser based on a solution of colloidal semiconductor nanoplatelets in a thin quartz cuvette.Wet-chemically synthesized colloidal semiconductor nanoparticles (whose spherical form is often referred to as quantum dots) are attractive as the active material in lasers because they (i) can easily be incorporated into almost any optical cavity; (ii) are straightforward to fabricate at industrially relevant quantities; (iii) exhibit different emission colours by simply varying their physical dimensions. However, their small size results in a highly efficient non-radiative process known as multiexcitonic Auger recombination. This makes it extremely challenging to achieve lasing with such particles, especially in the liquid phase where the concentration of nanoparticles is relatively low.A team led by Prof CHAN Yin Thai from the Department of Chemistry in NUS has demonstrated that semiconductor nanoparticles in the form of nanoplatelets can exhibit low threshold multi-photon pumped lasing in solutions when placed within a commercially available cuvette. The researchers also showed that the nanoplatelet cuvette-based laser showed no signs of photodegradation over many hours of continuous optical pumping. More importantly, the team demonstrated the existence of a pump threshold minimum as the lateral size of the nanoplatelets was varied (with all other conditions made the same).
The primary findings of this work provide guidelines for designing low threshold, solution-based semiconductor nanoparticle lasers. These solution-based lasers can easily be utilised in nonlinear optical sensors or for studying cavity behaviour in the presence of a chemically-tunable gain medium (see Figure).
Figure above shows a solution of colloidal semiconductor nanoplatelets in a thin quartz cuvette undergoing two-photon excitation (A) below and (B) above the pump threshold. (C) is the emission spectrum at various pump intensities. (D) Transmission electron microscope image of the nanoplatelets. [Image credit: CHAN Yin Thai]
Reference
Li M, Zhi M, Zhu H, Wu WY, Xu QH, Jhon MH, Chan Y. ”Ultralow-threshold multiphoton-pumped lasing from colloidal nanoplatelets in solution” Nat. Comm. 6 (2015) 8513.
