Optical properties of beta-Si3N4 single crystals grown from a Si melt in N-2

Large colored beta-Si3N4 single crystals were successfully grown from a Si melt in N-2. The transmission optical absorption of coloring beta-Si3N4 sin gle crystal shows that impurities introduce a midgap level of similar to 2. 4 eV into the wide band gap of similar to 5.3 eV in nondoped Si3N4. The inf rared transmission spectrum and electron probe x-ray microanalysis of beta- Si3N4 samples show that the solution of the Al element affects the silicon- nitrogen molecular vibration and the states within the band gap of beta-Si3 N4. The obtained results mean that the Al impurity acts as the radiative ce nter and is the origin of the color in the beta-Si3N4 single crystal. (C) 1 999 American Institute of Physics. [S0003-6951(99)02823-5].