Synthesis of luminescent thin-film CdSe/ZnSe quantum dot composites using CdSe quantum dots passivated with an overlayer of ZnSe

Electronic and chemical passivation of CdSe nanocrystals (quantum dots) has been achieved with a thin ZnSe overlayer grown in solution from trioctylphosphine selenide and diethylzinc. Layered particles with a [ZnSe/CdSe] ratio ranging from 0 to similar to 5.0 were prepared and characterized by optical absorption spectroscopy, photoluminescence, high-resolution transmission electron microscopy, Auger electron spectroscopy, and X-ray scattering. The overgrown particles were crystalline and displayed band-edge absorption and emission characteristic of the initial CdSe nuclei. Thin-film quantum dot composites incorporating bare and overcoated CdSe nanocrystals in a ZnSe matrix were synthesized by electrospray organometallic chemical vapor deposition (ES-OMCVD). The photoluminescence spectra of the composites with bare CdSe dots were dominated by broad deep-level emission and the photoluminescence yield deteriorated with increasing deposition temperature. In contrast, the composites incorporating the overcoated dots showed sharp band-edge emission. The presence of a preformed ZnSe layer resulted in a dramatic enhancement of the band-edge photoluminescence yield (by 2 orders of magnitude). The photoluminescence properties of composites with the passivated dots were insensitive to deposition temperature over the range studied.