Practical PPP molecular orbital calculations of absorption maxima of quinones.Part 2. Evaluation of the spectrochemical softness based on the absolute hardness

We report low temperature luminescence studies of a series of pure and treated anatase pigments. The intensity of the green excitonic emission correlated with the photoactivity of the pigment, recombination being enhanced in milled and coated samples. Weak emission was also detected from amorphous titania gels and the photocatalytically active Degussa P25 pigment. The latter gave no evidence for segregation of photocarriers because of the multiphasic nature of the material.