Impact of photoinduced processes on the plasmonic enhancement of colloidal quantum dot emission
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Impact of photoinduced processes on the plasmonic enhancement of colloidal quantum dot emission S. M. Sadeghi1,2 R. G. West1, and Kira D. Patty1 1 Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899, USA 2 Nano and Micro Device Center, University of Alabama in Huntsville, AL 35899, USA ABSTRACT We study the mutual effects of photoinduced processes (irradiation effects) and plasmonic emission enhancement in close-packed CdSe/ZnS colloidal quantum dots in the vicinity of gold metallic nanoparticles with two significantly different size distributions. For this we examine the impact of the heat generated by the metallic nanoparticles, the strength of plasmonic field enhancement, and the rate of energy transfer from the quantum dots to metallic nanoparticles in the presence of a laser field with low and moderate intensities. Our results show that the interplay between the photophysics of the quantum dots and their plasmonic emission enhancement is significantly pronounced when the metallic nanoparticles are large. In such a case we observed large suppression of photoinduced fluorescence enhancement (PFE). For smaller metallic nanoparticles the results suggest mostly an overall time-independent suppression of the quantum dots’ emission with no significant impact on PFE. INTRODUCTION The narrow emission spectra, tunability, and high quantum yields of colloidal quantum dots (QDs) have made them quite appealing candidates for various applications, including fluorescence probes for biomolecular and in vivo analytical applications, light emitting diodes, solar cells, etc. Currently significant research efforts are being devoted towards utilizing the plasmonic properties of metallic nanoparticles (MNPs) to improve the optical properties of QDs and envision new applications. This includes, for example, chemical and biological sensors [1,2], nano-devices [3], solar cells [4,5], etc. In addition to plasmonic emission enhancement, excitonplasmon coupling in QD-MNP systems have also been used for investigation of chemically or biologically triggered ultra-fast nanoswitches [6], exciton coherent dynamics and tunable Rabi oscillation [7,8], and sensors based on their molecular-like resonances (plasmonic metaresonances) [9]. A main feature of colloidal QDs, however, is that when they are irradiated, their fluorescence and physical structures can change significantly. One of the main reasons for this is the fact that the photophysics and photochemistry of such QDs strongly depend on the environment, including surrounding atmosphere, the impacts of QDs on each other, irradiation intensity, and even the substrate [10-12]. Irradiation of such QDs can increase their emission efficiencies (photoinduced fluorescence enhancement or PFE) or can suppress them via photooxidation. Many research activities have been devoted to explain the underlying mechanisms behind PFE. These include passivation of surface states by photoabsorbed molecules [13-14], photoinduced surface transformation or photoinduced rearrangement of c
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