A narrow-band UVB emitting phosphor is described wherein the phosphor has a preferred composition represented by the general formula (Y.sub.1-x-y-zGd.sub.xCe.sub.yPr.sub.z)MgB.sub.5O.sub.10 where x has a value in a range from 0.02 to 0.80, y has a value in a range from 0.01 to 0.97, and z has a value in a range from greater than 0 to 0.05 and x+y+z<1. The phosphor has a narrow emission centered at about 312 nm when excited by radiation from a low-pressure mercury discharge.