A UVB phosphor of the composition (Laj_,,—y—,Gd,,Yy)PO4:Ce, is described, in which x=0 to 0.5, y=0 to 0.5 and z=0.01 to 0.3 and the sum of x, y and z is less than 1. From a phosphor of this kind, a phosphor layer can be produced that, in fluorescent lamps based on low-pressure mercury discharge lamps, produces a spectrum of 5 UV light that is particularly well suited to the cosmetic or medical treatment of the skin.