Photoluminescence of the inorganic pigments Egyptian blue, Han blue and Han purple

The room-temperature photoluminescence spectra of various samples of Egyptian blue (CaCuSi(4)O(10)) are presented, discussed and compared with those of recently synthesized compounds corresponding to the ancient pigments Han blue (BaCuSi(4)O(10)) and Han purple (BaCuSi(2)O(6)). All the samples of Egyptian blue show identical spectra, in spite of their very different origin. The spectra of Han blue and Han purple are significantly different. Since the Cu(2+) ion may be considered the only luminescent centre in the spectral range under investigation, the differences between the spectra of the various pigments are ascribed to a ligand-field change. This can be related to the larger size of the Ba(2+) ion with respect to Ca(2+). The use of PL spectra for the identification of these pigments in works of art is proposed. (C) 2000 Editions scientifiques et medicales Elsevier SAS