Quantum confined Tb 3+ ion doped in YBO 3 nanocrystal yield enhancement in luminescence under 254nm (UV) excitation as compared to Tb 3+ ion doped in YBO 3 bulk phosphor. The terbium ion doped YBO 3 nanocrystals have particle size 9–20nm, while, YBO 3 :Tb 3+ bulk phosphor particles are of 100–300nm in size. Photoluminescence excitation peak shifts to higher energy with decrease of particle size. Enhanced luminescence in YBO 3 nanocrystal is explained on basis of modulation of f–f transition due to qunatum confinement of Tb 3+ ion in YBO 3 host. The enhancement in emission intensity in YBO 3 :Tb 3+ nanophosphor was not observed at 147nm (VUV) excitation. It is considered that the diminished emission intensity at 147nm excitation may be due to low penetration depth of VUV radiation as well as increase of surface defects responsible for non-radiative transition in nanoparticles.