Free Current Carrier Concentration and Point Defects in Bi2-xSbxSe3 Crystals

Organic nanocrystals of N-4-nitrophenyl- -prolinol (NPP) have been grown in sol–gel matrices prepared from silicon alkoxide precursors. Our process is based on the control of the nucleation and growth kinetics of the dye in the pores of dense gels. Nanocomposites gel–glasses are obtained with a high optical quality due to the small size of the nanocrystals (10–20 nm). Differential scanning calorimetry experiments evidenced clearly the melting point of NPP nanocrystals, which is registered 51°C above that of NPP powder. Micro-Raman and solid state NMR spectroscopies allowed us to demonstrate that our nanocrystallization process does not chemically modify NPP molecules. We specified also the nature of interactions existing between the NPP nanocrystals and the xerogels. These strong interactions, which explain the important increase of the melting point of the nanocrystals in comparison to the NPP powder, are hydrogen bonds between nitro groups of NPP and uncondensed silanol functions of the silicate network.