This paper describes and compares the local environments of Er3+ ions in pure SiO2, SiO2-Al2O3, SiO2-TiO2, and SiO2-HfO2, glasses, and in SiO2-HfO2 glass-ceramic waveguiding systems. This structural information is useful for selecting waveguides with optimised functional properties. This comparison has emphasised the peculiarity of the SiO2-HfO2 glass, in which the Er3+ ions are incorporated in HfO2-rich regions. By appropriate heat treatment, a transformation of SiO2-HfO2 system from glass to glass-ceramic occurs, where Er3+ remains incorporated in HfO2 nanocrystals as substituent of Hf4+. The spectroscopic interpretations are coherent with the present structural results.