The photoluminescence (PL) of high-quality CdSe nanocrystals (NCs) incorporated into polymer thin films was found to respond reversibly and rapidly to environmental changes upon photoradiation above their absorption onset. The PL of the NCs may be dramatically enhanced or diminished depending on the properties of the gases. Photostimulation was found to be necessary for the response, which likely makes the original dense-ligands monolayer on the surface of the NCs permeable to gases by the activation of the vibration modes of the NC lattice through photon−phonon coupling.

We report our systematic studies of the environmental effects on the photoluminescence (PL) from colloidal CdSe nanocrystals (NCs) embedded in polymer thin films. The highly luminescent bare-core CdSe NCs were significantly more robust than the core/shell CdSe/ZnS NCs against photoannealing under inert environments, while the core/shell NCs are more resistant to photooxidation. For the case of bare-core NCs, we show the importance of the initial photoactivation as the proper treatment for subsequent studies, a step that is basically irrelevant in the case of core/shell NCs. By measuring the PL wavelength shift, PL line width, and PL intensity, we investigated the dynamic changes of the emission properties of these NCs under different environments, including argon, oxygen, air, water vapor, and wet oxygen, and under different excitation conductions to reveal the photoinduced nature of the interactions between the nanocrystal surface and the environment. Mechanisms related to photoactivation, photooxidation, and PL enhancement are briefly discussed.

Material and optical characterizations have been conducted for epitaxially grown Ge1−xSnx thin films on Si with Sn composition up to 10%. A direct bandgap Ge0.9Sn0.1 alloy has been identified by temperature-dependent photoluminescence (PL) study based on the single peak spectrum and the narrow line-width. Room temperature PL emission as long as 2230 nm has also been observed from the same sample.

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