We present a detailed investigation on the effect of functional group modulation at the edges of carbon quantum dots (CQDs) on the fluorescence from the CQDs. The CQDs attached by N, S, and P elements are synthesized via pyrolysis of a mixture of citric acid and NH 3 H 2 O, H 2 SO 4 , and H 3 PO 4 , respectively. Thus, part of –COOH at the edges of CQDs can be converted into –C=O and functional groups such as –NH 2 , –SO 2 , –HSO 3 , and –H 2 PO 4 can connect to the carbon bonds. We find that the formation of the N/S/P-CQDs can reduce the amount of –COOH that attaches to the edges of sp 2 -conjugated π -domains located at centers of these CQDs. This effect can result in the reduction of the non-radiative recombination for electronic transition in these CQDs. As a result, the quantum yield (QY) for fluorescence from the CQDs can be efficiently enhanced. We demonstrate experimentally that the QYs for N/S/P-CQDs can reach up to 18.7%, 29.7%, and 10.3%, respectively, in comparison to 9% for these without functional group modulation. This work can provide a practical experimental approach in improving the optical properties of fluorescent CQDs.

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Temperature dependence of dark current (I d) and photocurrent (I ph) is reported for Si-based amorphous HgCdTe (a-MCT) infrared photoconductive detector at 80-300 K. It is indicated that an uncooled a-MCT infrared detector can be fabricated based on the Si-based a-MCT. To describe the transport process, the Mott and Davis model [Davis and Mott, Philos. Mag. 22, 903 (1970)] is proposed as the conducting model originally developed for amorphous silicon. A possible mechanism of the carrier transports is shown in the a-MCT materials. The transport transition between the localized and extended carriers leads to the maximal I ph /I d above 200 K. V

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