We fabricated three series of glasses in which the Y 2 O 3 , Bi 2 O 3 and Al 2 O 3 contents of Bi-doped Y 2 O 3 :Al 2 O 3 :SiO 2 glass were varied. We optimized the content of each component based on quantum efficiency (QE) and other optical properties. The strength of the Bi absorption bands decreased with increasing Y 2 O 3 content. The optimized composition was: 63.5SiO 2 :22.5Al 2 O 3 :13Y 2 O 3 :1Bi 2 O 3 . With 808nm excitation this glass had a QE, lifetime, emission width and peak of 20%, 375μs, 293 and 1240nm, respectively. The Bi absorption strength had a quadratic dependence on Bi 2 O 3 content. This indicates that the optically active Bi center is Bi 2 dimers.