| Taking the advantages of simple synthesis process,uniform size and morphology,high refractive index,tunable band gap,and narrow exciton line-width,lead halide perovskite quantum dots(PQDs)have attracted significant attention as potential candidates for single photon emitter in nanophotonics.However,the slow spontaneous emission of PQDs at room temperature(excition lifetime ranging 2?30 ns)makes it difficult to match the needs of high-speed photonic sources.In this thesis,the Purcell effect generated by exciton-plasmon coupling is used to increase the spontaneous emission intensity and rate of the thin solid films of PQDs.The effects of silver nanostructures,polymer spacer,as well as the excitation light characteristics on the spontaneous emission intensity and rate of PQD thin films are explored to provide guidance for the development of bright and fast PQD-based photonic source.The main results are achived as follows:Using cesium carbonate and lead halide as precusors,oleic acid and oleylamine as ligands,and octadecene as reaction media,monodisperse colloidal nanocubes(sub-10 nm edge lengths)of fully inorganic cesium lead halide perovskites(Cs Pb X3,X = Cl,Br,and I or mixed halide systems Cl/Br and Br/I)were prepared via the hot-injection method.The bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410?700 nm through compositional modulations.The photoluminescence of Cs Pb X3 nanocrystals is characterized by narrow emission line-widths of 14?40 nm,high quantum yields of up to 90%,and fluorescence lifetimes in the range of 2?30 ns.The anisotropy of fluorescence emission of PQD solution was studied by polarized fluorescence spectra.It was found that the depolarizations of both emission and excitation spectra are close to the unity.A series of planar devices are produced in large scale via chemistry assembly using colloidal Cs Pb Cl0.75Br2.25 QDs,Ag nanoparticles with a diameter of 55 nm,and polyvinylpyrrolidone(PVP)as building blocks.By varying the PVP spacer thickness as well as Ag nanocube surface density,a tunable photoluminescence enhancement is realized in both steady and time-resolved measurements,showing a 3.5-fold enhancement in the total fluorescence intensity and simultaneously an increase in the emission rate of a factor of 4.5.Due to the different functional response of the steady PL enhancement factor and Purcell factor to PVP spacer,it is possible to design a plasmonic encryption device by using nonluminescent and printable PVP inks to encrypt the information,which is difficult to crack by conventional UV irradiation.Our results present a large cavity quantum electrodynamics effect in a planar structure of lead halide perovskite-based quantum emitters with fast emission,spectral tunability,and scalable production,which suggest a route to extend such effects to the hybridintegration using solution chemistry assembly.A series of planar devices are produced in large scale via chemistry assembly using colloidal Cs Pb Cl0.75Br2.25 QDs and silver nanowire(Ag NW)with a diameter of 40 nm and an aspect ratio of 1000,in which polyvinyl alcohol(PVA)is used as a spacer to regulate the lossy characteristics of the plasmonic cavity.Compared with bare quartz,the PVA substrate shows a considerable enhancement effect on the apparent emission intensity,but a reduction in the emission rate of PQD excitons.The efficient NWK-PQD coupling generates an increase in the emission intensity of a factor of 6.0(average 3.4)and simultaneously a 2.4-fold(average 1.9)enhancement in the emission rate.By tuning the PVA spacer thickness,three different spontaneous emission features for NWK coupled PQDs with dark-fast,bright-fast and bright-slow zones are identified in terms of Purcell factor and emission quantum yield. |
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