Photoluminescence spectroscopy of Cr3+ in ceramic Al2O3

Photoluminescence (PL) spectroscopy is applied to study the radiative processes of ceramic Al2−xCrxO3 (0.002≦x≦0.15) with the excitation light of 295 nm wavelength together with the optical absorption characterization by photoacoustic (PA) spectroscopy. I (694 nm), the relative intensity of R line (∼694 nm) for ceramic Al2−xCrxO3, decreases with increasing mole fraction x, indicating the concentration quenching by the increase of interaction between Cr3+ ions. I (704 nm) and I (775 nm), those of N line (∼704 nm) and broad band (∼775 nm), increase with increasing mole fraction x, indicating the increases of pair state of Cr3+ ions (N line) and the state by groups of more than two Cr3+ ions (broad band). The ratios, I (704 nm)/I (694 nm), increases linearly with increasing mole fraction x up to 0.15, indicating that it is different from the early results under the assumption that the states of pair and groups of more than two Cr3+ ions obtain some excitation by energy transfer from single ions.