Cadmium selenide nanocrystal quantum dots: From fundamental physics to optical nanodevices

The optical properties of CdSe nanocrystal quantum dots (NQDs) have been studied experimentally. Femtosecond transient absorption spectroscopy is applied to investigate carrier dynamics and mechanisms responsible for the development of the optical gain and stimulated emission in NQD samples. An analysis of pump-dependent nonlinear absorption signals for solid-state NQD films indicates that the optical gain is due to the multiparticle states with the dominant contribution from the doubly excited nanoparticles (biexcitons). Optical gain dynamics are controlled by Auger recombination of biexcitons. Despite the theoretical predictions of temperature independent optical gain the regime of stimulated emission is achieved more easily at cryogenic temperatures. It is determined that ultrafast hole trapping is responsible for this observation.; Studies of nonlinear optical signals in solution-based NQD systems reveal the presence of photoinduced absorption (PA) overlapping with the region of the optical gain. Strong size dependence of the PA on the particle size is observed. For small NQD sizes PA completely suppresses optical gain.; Development of stimulated emission (SE) in solid-state NQD films is observed. In addition to SE, true lasing action using NQDs incorporated into microcapillary tubes is demonstrated. This demonstration indicates the feasibility of miniature solid-state laser devices based on NQDs. NQD films are also used to demonstrate efficient dynamic gratings. These gratings can be applied for ultrafast switching and optical correlation devices. These results show large potential for the NQD-based devices, particularly for the use in optical communication technologies.