Effect of Heat-Treatment and Composition on Structure and Luminescence Properties of Spinel-Type Solid Solution Nanocrystals

The compositional dependence of the structure and properties of spinel-type solid solutions, Zn(Al,Ga)(2)O-4 was investigated by comparison with samples hydrothernnally prepared and those after heat treatment at 1000 degrees C in air. Nanocrystalline spinel-type solid solutions in the whole composition range in the ZnAl2O4-ZnGa2O4 system were directly formed from the aqueous precursor solutions of ZnSO4, Al(NO3)(3) and Ga(NO3)(3) under hydrothermal conditions at 180 degrees C for 5 h in the presence of tetramethylammonium hydroxide. The incorporation of aluminum into the lattice, Zn(AlxGa1-x)(2)O-4, resulted in lower crystallinity of the spinel. The relationship between the lattice parameter of as-prepared samples and the Al atomic ratio in the spinel composition was slightly apart from the ideal linear relationship that was obtained in the samples after heat treatment at 1000 degrees C. The optical band gap of both as-prepared solid solutions and those heat treated linearly increased from 4.1 similar to 4.2 to 5.25 eV by the incorporation of aluminum ion into the lattice, Zn(AlxGa1-x)(2)O-4. Two main broad-band emission spectra centered at around 360 and 430 nnn in the range of 300 similar to 600 nm were observed in the spinel solid solutions under excitation at 270 nm, thought their broad-band emission spectra and their peak wavelengths subtly changed depending on the composition and heat treatment.