This work assesses the incorporation of dopant ions such as Al3+, Ga3+, Zr4+, Nb5+, Ta5+ and Er3+ into the core of germanosilicate optical fibres via modified-chemical-vapour-deposition plus solution doping fabrication techniques. We find that highly-charged smaller ions, like Al3+ and Ta5+, behave similarly. These ions are more efficiently incorporated, assist in the incorporation of Er3+, and have the same influence on the fluorescence spectra of Er3+. The structural role of these ions appear to be their ability to provide nonbridging oxygens around Er3+. The waveguide and lasing characteristics of Er3+ codoped with Ta5+ are presented.