XRF revealed Mo content in every set of crystals, including the separated tip lacking the green-yellow hue. Accounting for Eu and Mo only, XRF results range from 0.33(2) at% to 5.55 (8) at% Mo (99.67 at% to 94.45 at% Eu). Mo 3+ and Mo 5+ ions can incorporate due to excess molybdenum in the flux, which by stoichiometry should only include Mo 6+ . Mo 3+ inclusions are expected to substitute preferentially on Al 3+ sites and can quench fluorescence in EuAl 3 (BO 3 ) 4 . Even though the K 2 Mo 3 O 10 flux does not significantly reduce inclusions when compared to Bi 2 O 3 -B 2 O 3 , the Mo ions' preference for Al 3+ sites may reveal the influence of non-rare-earth site substitutions on stoichiometric compounds' inhomogeneous linewidths. In comparison, for Eu 3+doped Y 2 SiO 5 , additional percent-level substitutions of Sc 3+ on Y 3+ sites led to a 50-fold increase in inhomogeneous linewidth.