Photo-quenched of the luminiscence signal in Co(II)-doped alumina prepared by the sol–gel method

Co(II)-doped alumina monoliths prepared by the sol–gel method were laser irradiated producing fluorescence. The intensity of this defect-induced fluorescence was exponentially reduced with the irradiation time to practically disappear. The rate the fluorescence intensity decays was modeled as a double exponential function of the irradiation time; the characteristic times associated with the decays are in the range of seconds. The suppression of the luminescence was associated with the local heating produced by the highly focused laser beam in a small area (≈ 2 μm in diameter) on the sample. This heating process reduces physical (grain boundaries and surface states) and chemical (oxygen vacancies) defects present in the sol–gel samples. Some residual fluorescence still remains after long periods of illumination. The characteristic times for alumina samples are compared with those obtained for other metal oxides prepared also by the sol–gel method.