As can be seen from Table 2, for the undoped LaPO4 samples the Raman peak of ν1(A1) modes is at 974.6 cm 1 with FWHM of 5.5 cm 1 and when increasing Tb3 þ dopant concentration up to 20 mol%, the corre- sponding Raman peak of ν1(A1) modes is at 979.1 cm 1 with FWHM of 12.9 cm 1, i.e. is shifted by 5.5 cm 1 and broadened by 7.4 cm 1 towards the higher frequency.