The invention is a tape cartridge including a single tape reel around which a length of magnetic tape is wound and which is turnably held within a housing. The blue phosphor is a compound represented by Ba1-xMgAl10O17:Eux or Ba1-x-ySryMgAl10O17:Eux, wherein 0. The degree of stretching varies across the width of the tape in proportion to the degree and local density of the selective perforations.