This paper presents some encouraging features on Tb3+-doped LaPO4, used for the first time as nanoparticles (NPs) for photo-structured composite material. First, LaPO4:Tb3+ nanorods are hydrothermally synthesized. TEM analysis point out that their size distribution and their morphology are well defined. Then, a small amount of NPs (2 or 3.9 wt%) is dispersed in acrylate monomers mixture and the photo-patterning is performed by using holography, a technique among the others. It is interesting to note that even if the loading of the NPs is weak, these last ones significantly influence the physical properties of the gratings. Indeed, the observed increase in the refractive index modulation depth is ascribed to both phenomena: the sequestration of LaPO4:Tb3+ nanorods within the periodic structure and the change in the kinetics of photopolymerization. The localization of NPs in the non-illuminated zones, evidenced by fluorescence microscopy, is favoured by the decrease in the rate of polymerization, revealed by infrared spectroscopy.