MODULATION ON POSITIONS OF OPTICAL-ABSORPTION BANDS IN POROUS AL2O3 HOST CR2O3

The optical absorption properties of porous Al2O3 host/Cr2O3 nanocompo sites were investigated. The results show that for each optical reflec tion spectrum, four absorption bands (p(1)-p(4)) occur in the waveleng th range 200-800 nm. The p(2), p(3) and p(4) bands are induced by the Cr3+ 3d(3) electronic transitions from the (4)A(2) ground-state energy level to the excited-state energy levels: T-4(1), T-4(2) and T-4(2)' (T-4(2)' is formed from splitting of T-4(2)), respectively. The appear ance of p(1) is closely related to the Cr3+ and Cr4+ ions. For porous Al2O3 host/Cr2O3 nanocomposites, which are formed by assembling the po rous Al2O3 host With nano-Cr2O3 particles, the positions of absorption bands can be modulated by means of pyrolysis of Cr(NO3)(3) at differe nt temperatures in air, reducing the samples in high purity H-2 and th e size confinement of Cr2O3 particles by voids in the Al2O3 host. With increasing pyrolysis temperature, a blue shift of the absorption band s appears and, inversely, a red shift of the absorption bands takes pl ace when heating the samples in H-2.