“…The PL blue shift for Sr 3 YAl 2 O 7.5 :Eu, due to the Eu 2+ at the Y 3+ site, suffers an insignificant centroid shift, and the crystal‐field splitting, due to Y 3+ , has a larger ion radius than that of Lu 3+ (IR = 0.86 Å for CN = 6). [ 10 ] The slightly narrower emission and smaller Stokes shift for Sr 3 YAl 2 O 7.5 :Eu are related to the more restricted structural relaxation for Eu 2+ on the larger Y 3+ site. [ 16–17 ] Identical emission behaviors were found in our previously studied narrow‐band MBe 2 (PO 4 ) 2 :Eu 2+ (M = Ca, Sr) phosphors, wherein Eu 2+ is located at the larger Sr 2+ site, showing narrower emission, smaller Stokes shift, and higher emission energy as compared to that of Eu 2+ at the Ca 2+ site.…”