Colouring Mechanism of Red Ceramic Pigments Based on Perovskite Structure

The origin of colour in Cr-doped ceramic pigments with AIIIBIIIO3 perovskite structure was investigated by high resolution X-ray diffraction and LTV-Vis-NIR spectroscopy. The development of red colour is related to different phenomena: symmetry lowering from hexagonal (Nd) to orthorhombic (Sm-Yb); crystal field strength decrease due to an octahedral tilting distortion with longer (Al,Cr)-O distances in HREE perovskites; shift of a broad absorption band in the bluegreen spectrum depending on the lanthanide ion.