Photoluminescence Properties Of CdSe Quantum Dots

The quantum dots (QDs) have the good properties about the spectral tenability, light stability and chemical versatility. In recent years, there are many reports about the physical and chemical properties of QDs, as well as their application in the field of optoelectronics, for example,quantum laser rods, CdSe/ZnS quantum dot lasers, solar cells, etc..In this work, the QDs are marked from NO.1 to NO.5 according to the chemical reaction time increasing at a same time interval. All the samples undergo the UV-visible absorption and the photoluminescence (PL) experiments, the absorption peaks are followed by the 532 nm,552 nm,566 nm,573 nm and 583nm, and for the PL results, they are 558 nm,575 nm,585 nm,591 nm and 600 nm respectively. Thus, with the reaction time increasing, the absorption peak has a red shift. The different samples exhibit size-tunable PL spectrum. After spin-coating the QDs on the Ag particles, we conducted PL experiment of the samples. It is found that when the Ag particles with a thickness of 30 nm as deposited, and annealed at 150℃for 1h, the PL intensity of the QDs/Ag sample is enhanced by 4.6 times. Then ZnS as the insulating layer was embedded between the Ag particles and the QDs.Because of the good photo stability and the low cost of the QDs, we mainly studied the CdSe quantum dot microcavity formed between two distributed Bragg reflectors (DBRs). The active region consisting of CdSe quantum dots embedded in PMMA. We used the transfer matrix method (TMM) to simulate the reflectivity spectrum of the microcavity. An enhancement of the spontaneous emission from the colloidal CdSe quantum dots in the microcavity is demonstrated. After embedding the QDs in the cavity, the full width at half maximum (FWHM) is narrowed down to 7.5nm compared with that of QDs in free space about 27.9 nm. The emission of the quantum dots is enhanced by a factor 3.7 due to the microcavity effect.The periodic arrays of Ag islands were prepared by the polystyrene spheres (PSs) template method. The QDs were spin coated on the Ag islands with the concentration of 8×1015/ml. In the PL experiments, we collected the information from the area of 1um×1um, the PL intensity ratio of the defect emission compared with the band-edge emission is changed from 1:20 to 1.2:1. So it is possible to characterize the photoluminescence properties of the QDs on the islands of Ag particles in the small size range.