Titanium dioxide (TiO2) nanoparticles were prepared by the sol-gel method at different pH values (3.2–6.8) with a hydrochloric acid (HCl) solution. Raw samples were calcined at 500 °C for 2 h. The effects of pH on the structural, morphological and optical properties of TiO2 nanoparticles were investigated. At pH 4.4–6.8, only the anatase phase of TiO2 was observed. Under strong acidic condition at pH 3.2 rutile, brookite and anatase co-exist, but rutile is the predominant phase. The strain value increased and the crystallite size decreased as the HCl content increased. The increased crystallite sizes in the range 21–24 nm and enhanced blue emission intensity around 432 nm was obtained for the sample at pH 5.0. Experimental results showed that TiO2 nanoparticles synthesized at pH 5.0 exhibited the best luminescence property with pure anatase phase.

Cu2Zn(Sn1− x In x )Se4 bulks with x = 0–0.6 were prepared by a liquid–phase reactive sintering method at 600 °C. Defect chemistry was studied by measuring electrical properties of In-doped CZTSe (In–CZTSe) as a function of dopant concentration. With increasing the x value from 0 to 0.6, the carrier concentration of In–CZTSe increased from 1017 to 1019 cm−3 but the hole mobility greatly increased from 1.23 cm2 V−1 s−1 to a maximum value of 8.0 cm2 V−1 s−1 then decreased to about 1.4 cm2 V−1 s−1 at x = 0.6. The largely increased carrier concentration and the slightly changed lattice parameters for In–CZTSe with increasing the In content are related to the precipitated In-rich Cu2 B II B IVSe4 compound and the types of their defects such as InSn and B Cu.

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