This research studied the preparation of luminescent glasses using 18SiO2-35B2O3-22ZnO-20K2O glass frits. The glass frits were first mixed with 15 wt.% of commercial SrAl2O4:Eu2+,Dy3+ phosphors and different B2O3 concentrations of 0-15 wt.%. The raw materials were then melted at 750-800°C for 1 hr. The results showed that the addition of B2O3 as a flux induced the crystallization of α-Zn2SiO4 phase and suppressed the luminescent properties of phosphor-in-glasses. This could be due to the dissociation of SrAl2O4 by the reaction of SrAl2O4 and B2O3. The higher sintering temperature at 800°C also further degraded the luminescent properties as a result of further phosphor degradation and the oxidation of Eu2+.