CuCr 1−x Mg x O 2 , a wide band gap semiconductor with the delafossite structure, has been synthesized in bulk and thin-film form. Bulk undoped CuCrO2 is almost black and has moderate conductivity with p-type carriers. Upon doping with 5% Mg, the conductivity increases by a factor of 1000. In films, the best p-type conductivity is 220 S cm−1 in CuCr0.95Mg0.05O2, a factor of 7 higher than previously reported for Cu-based p-type delafossites. Undoped films have a conductivity of order 1 S cm−1. Films are usually polycrystalline on amorphous substrates, but undoped films can be c-axis oriented if deposited at or above 650 °C. Optical and ultraviolet transmission data indicate a direct band gap of 3.1 eV.

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The electronic structures of Cu2S and CuS have been under intense scrutiny, with the aim of understanding the relationship between their electronic structures and commercially important physical properties. Here, X-ray absorption and emission spectroscopic data have been analyzed using a quantitative, molecular orbital (MO) based approach to understand the electronic structure of these two complex systems. Cu2S is shown to have a significant amount of Cu2+ sites and therefore Cu0 centers. The presence of low-valent Cu is correlated with the electrical conductivity of Cu2S, especially at high temperatures. CuS is shown to have tetrahedral Cu2+ and trigonal Cu1+ sites, with crystal planes that have alternating high and low charge on the Cu centers. These alternating charges may contribute to internal energy transitions required for photoluminescence properties. The in-depth electronic structure solutions presented here not only solve a complicated much-debated problem, but also demonstrate the strength of quantitative MO based approach to X-ray spectroscopies

Heavily F-doped SnO(2) nanocrystals were successfully prepared by a novel synthetic approach involving low-temperature oxidation of a Sn(2+)-containing fluoride complex KSnF(3) as the single-source precursor with H(2)O(2). The F-doped SnO(2) powder was characterized by powder X-ray diffraction, TG-MS, BET surface area, diffuse reflectance spectroscopy, XPS, PL, FTIR spectroscopy, Raman spectroscopy, EPR spectroscopy, SEM, and TEM. Broadening of the diffracted peaks, signifying the low crystallite size of the products, was quite evident in the powder X-ray diffraction pattern of SnO(2) obtained from KSnF(3). It was indexed in a tetragonal unit cell with lattice constants a = 4.7106 (1) Å and c = 3.1970 (1) Å. Agglomeration of particles, with an average diameter of 5-7 nm, was observed in the TEM images whose spotwise EDX analysis indicated the presence of fluoride ions. In the core level high-resolution F 1s spectrum, the peak observed at 685.08 eV was fitted by the Gaussian profile yielding the fluoride ion concentration to be 21.23% in the SnO(2) lattice. Such a high fluoride ion concentration is reported for the first time in powders. SnO(2):F nanocrystals showed greater thermal stability up to 300 °C when heated in a thermobalance under flowing helium, after which generation of small quantities of HF was observed in the TG coupled mass spectrometry analysis. The band gap value, estimated from the Kubelka-Munk function, showed a large shift from 3.52 to 3.87 eV on fluoride ion doping, as observed in the diffuse reflectance spectrum. Such a large shift was corroborated to the overdoped situation due to the Moss-Burstein effect with an increase in the carrier concentration. In the photoluminescence (PL) spectrum, SnO(2):F nanocrystals exhibited a broad green emission arising from the singly ionized oxygen vacancies created due to higher dopant concentration. The evidence for singly ionized vacancies was arrived from the presence of a signal with a g value of 1.98 in the ESR spectrum of SnO(2):F at room temperature. The disordered nature of the rutile lattice and the enormous oxygen vacancies created due to fluoride ion doping were evident from the broad bands observed at 455, 588, and 874 cm(-1) in the room-temperature Raman spectrum of SnO(2):F. As the consequence of the oxygen vacancies, F-doped SnO(2) was examined for the function as a photocatalyst in the degradation of aqueous RhB dye solution under UV irradiation. A very high photocatalytic efficiency was observed for the F-doped SnO(2) nanocrystals as compared to pure SnO(2). The BET surface area of pure SnO(2) was quite high (207.81 m(2)/g) as compared to the F-doped SnO(2) nanocrystals (45.16 m(2)/g). Pore size analysis showed a mean pore diameter of 1.97 and 13.97 nm for the pure and doped samples. The increased photocatalytic efficiency was related to the very high concentration of oxygen vacancies in SnO(2) induced by F doping.