Stepan Ya. Kuchmiy

Preparation and optical properties of highly luminescent colloidal single-layer carbon nitride

Thermal treatment of graphitic carbon nitride (g-CN) in aqueous solutions of tetraethyl ammonium hydroxide at ∼100 °C yields transparent colloidal solutions retaining stability at a CN concentration of up to 50 g L−1 and upon dilution by a factor of 103. Atomic force microscopy showed that the major part of the CN particles in diluted colloidal solutions are characterized by a lateral size of around 30–50 nm and a thickness of 0.3–0.4 nm typical of a single CN layer. Besides, a small fraction of multi-layer 2–5 nm thick g-CN particles with a size of ∼60 nm is present in the solutions. Photoexcitation of the colloidal CN near the edge of the absorption band results in emission of strong broad-band photoluminescence with a maximum at 460–470 nm and a quantum yield of 45–50%.

Colloidal ZnO nanocrystals in dimethylsulfoxide: a new synthesis, optical, photo- and electroluminescent properties

Stable colloidal solutions of zinc oxide in dimethylsulfoxide were synthesized via interaction between zinc(II) acetate and tetraalkylammonium hydroxides (alkyl-ethyl, propyl, butyl, and pentyl). Colloids of ZnO emit photoluminescence in a broad band with a maximum at 2.3-2.4 eV with quantum yields of up to 9-10% at room temperature and 15-16% at 80 K. The photoluminescence is supposed to originate from the radiative recombination of conduction band electrons with holes captured by deep traps having corresponding states in the band gap 1.0-1.2 eV above the valence band edge. The size of colloidal ZnO nanocrystals depends on the duration and temperature of the post-synthesis treatment and varies in the range of 3-6 nm. Growth of the ZnO nanocrystals can be terminated at any moment of the thermal treatment by freezing the colloidal solution or by addition of tetraethyl orthosilicate which hydrolyses forming core-shell ZnO@SiO2 particles. ZnO nanocrystals introduced into polyethyleneimine films can be used as an active component of an LED emitting at an applied voltage higher than 13 V.

A spectroscopic and photochemical study of Ag+-, Cu2+-, Hg2+-, and Bi3+-doped CdxZn1−xS nanoparticles

A combination of stationary and time-resolved absorption and photoluminescence spectroscopy with flash and steady-state photolysis of Ag(+), Cu(2+), Hg(2+), or Bi(3+)-doped Cd(x)Zn(1-)(x)S nanoparticles was used to assess the nature of the doping influence upon the optical properties of Cd(x)Zn(1-x)S nanoparticles. The relationships between the type and the concentration of a dopant and the dynamics of the photoinduced processes in the doped nanoparticles are derived and discussed. A correlation is found between the magnitude of doping-induced changes in the intensity and decay dynamics of the deep trap photoluminescence and an enhancement of the transient bleaching recovery and acceleration of the photocorrosive degradation of the doped Cd(x)Zn(1-x)S NPs compared to the undoped ones. The impact of the dopant upon the intensity of the luminescence and microsecond transient bleaching bands was found to grow substantially from Ag(+) to Cu(2+), Hg(2+) and Bi(3+). The same trend was found to hold for the acceleration of the steady-state photochemical corrosion of doped Cd(x)Zn(1-x)S nanoparticles. The differences among the effect of the dopant ions studied were interpreted in terms of the depth and charge of surface states created by Cd(2+) (Zn(2+)) substitution by a dopant.