Lasing from CdSe/ZnS Quantum Rods in a Cylindrical Microcavity
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Lasing from CdSe/ZnS Quantum Rods in a Cylindrical Microcavity Miri Kazes, David Y. Lewis, Yuval Ebenstein, Taleb Mokari and Uri Banin Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Isreal
ABSTRACT Lasing from CdSe/ZnS quantum rods and quantum dots both in solution and in a film is studied by utilizing a high Q cylindrical microcavity, showing Whispering Gallery Mode (WGM) lasing. CdSe/ZnS quantum rods, in comparison to quantum dots, exhibited remarkably reduced lasing thresholds. In addition, polarization measurements revealed that quantum rods have a linear polarized lasing, in contrast to quantum dots that show no preferable lasing polarization. Furthermore, an efficient and reproducible method is employed for preparation of nanocrystal films inside capillaries by laser irradiation for achieving robust lasing. Further irradiation of the film resulted in a room temperature stable lasing over hundreds of pump pulses, lasing thresholds as low as 0.02mJ and lasing intensities that are three orders of magnitude larger than the saturated fluorescence intensity. This was successfully applied to CdSe/ZnS quantum rod samples of varied dimensions and was also demonstrated for quantum dot samples.
INTRODUCTION Semiconductor nanocrystals show potential for applications ranging from photonics and resonator on-a-chip devices to biosensing. An obvious advantage of such nano particles is the remarkable spectral coverage for luminescence that is afforded via the quantum confinement effect by merely controlling the size and composition of the nanocrystals using well-developed colloidal synthesis [1,2]. Recent synthesis efforts led to the shape control of such colloidal prepared CdSe nanocrystals by a modification of the colloidal synthesis to obtain rod shaped particles – quantum rods [3,4,5]. In contrast to the spherical shaped quantum dots, quantum rods have linearly polarized emission as demonstrated by single crystal measurements and theoretical calculations [6,7]. Nanocrystal's low dimensionality is expected to provide low lasing thresholds and lasing that is insensitive to temperature thus making the nanocrystals interesting new candidates as optical gain materials. However, there are also very fast loss mechanisms and mainly the fast Auger recombination process that prevents efficient lasing [8,9]. In order to overcome the losses we utilize glass capillary tubes that serve as both convenient microcontainers for the samples i.e. the gain medium, as well as the microcavity for Whispering Gallery Mode (WGM) lasing [10,11]. The short round-trip times in the microcavities and the very high quality factors make it possible to compete with rapid loss mechanisms that counteract population inversion necessary for lasing [12].
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EXPERIMENTAL DETAILS The CdSe quantum dots were grown using the methods of colloidal nanocrystal synthesis utilizing high temperature pyrolysis of organometallic precursors in coordinating solvents and are overco
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