The introduction of SiO2 affects the glass's micro-structure and micro-defects as well as the corresponding optical and physical properties of the B2O3-containing multicomponent phosphate glasses. The addition of SiO2 increases the transition temperature and causes shifts of the UV cut-off wavelength (lambda(cut-off)). The changes of lambda(cut-off) are closely related to the PO3-EC and PO4-EC defect centers that are associated with the Q(2) tetrahedral in phosphate chains. The corresponding variations of Q(2) units can also be found in the Raman, XPS, and P-31 MAS-NMR spectra. With increasing the content of SiO2, the ratio of nonbridging oxygen (associated with Q(2) units) is gradually decreased down to a critical level when SiO2/B2O3 ratio is 4/1.5, whereas the ratio of non-bridging oxygen increases when SiO2/B2O3 ratio is larger than 4/1.5, which suggests that the doping SiO2 can influence the concentration of PO3-EC and PO4-EC defects. Those results can be better obtained when the sample is exposed to gamma irradiation. As the SiO2 content increased gradually up to 4/1.5, the concentration of the PO3-EC defects declined, while the concentration of PO4-EC and the POHC defects increased when considering the irradiation dose, indicating that the addition of SiO2 can regulate the structure-related defects in phosphate based glasses. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement