Origins of colour in Yb–Si–Al–O–N glasses

Previous work has shown that some RE-Si–Al–O–N glasses are coloured. In particular, oxynitride glasses containing Ytterbium were observed to display a wide range of colours depending on their composition. The reasons for this were not immediately evident. As Ytterbium and Europium have been reported to display valency variations in silicate glasses and α-sialons, the current study prepared a range of Yb–Si–Al–O–N glasses, characterised them by means of X-ray photoelectron, Raman, FTIR and UV–vis spectroscopy as well as thermal analysis and X-ray diffraction. The correlation between the structural features of the glasses with the changes in colour occurring when varying the Yb:Al ratio were investigated. Ytterbium garnet was found to be the source of colour change in the Yb–Si–Al–O–N in the compositions studied.