Blue-shift of absorption edge in LaTiO2N by controlling the anion nonstoichiometry

The perovskite-type oxynitride LaTLiO2N was prepared by heating an oxide precursor at 950 degrees C for 5 hours under NH3 atmosphere at a flow rate of 1 dm(3)/min. The precursor was prepared by the polymerized complex method. The oxynitride obtained was almost stoichiometric, LaTi(O0.68N0.32)(2.9), with a reddish orange color. The oxynitride was successively annealed at 950 degrees C for 3 hours under a NH3 atmosphere at flow rates of 50 cm(3)/min, 30 cm(3)/min and 10 cm(3)/min, respectively. The color and composition varied from yellow LaTi(O0.89N0.11)(2.8) through green-yellow LaTi(O0.93N0.07)(2.9) to light-blue LaTi(N-0.98(0.02))(2.9) in accordance with the decreased flow rate. The absorption edges varied from 2.28 eV for the reddish orange, 2.56 eV for the yellow, 3.17 eV for the green-yellow, to 3.44 eV for the light-blue oxynitrides. Annealing under NH3 is therefore effective in color tuning, mainly resulting in a blue-shift of the absorption edge. DV-X alpha calculations support the conclusion that the lower flow rate of NH3 led to a lower amount of nitrogen and higher oxygen levels in the oxynitrides. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.