S 38677 The point defects in ferroelectrics may influence the physical properties of phononic crystals LiTaO3 (LT) and LiNbO3 (LN). The initial wafers, periodically poled (PP) structures of LT with 1-mm-domains, and PP-LN with 0.45-mm-domains are investigated. Photoluminescence (PL) is taken at room temperature 310-nm -excitation. The slit width in optical spectrometer is set to 1 nm. The PL spectra of LT reveal multiple impurities including Fe + ,W, Th, Cs, Kr, Cu, Xe. Unlike PL from LN, there are no lines of the F-center, Ar and some other elements. The intensities of PL-lines in both LT and LN demonstrate a saw-type periodicity along the direction normal to the Z-axis. For instance, the PL line of Fe + defect in LT varies ± 15% with periodicity about 200 ± 40 nm. In the case of PP LT phononic crystals, the difference in Fe + line amplitude remains about the same; however, the periodicity becomes equal to a ferroelectric domain length of 1 mm. There is a difference between the two periodicities of charged defects in PP-LT and PP-LN; the positions of maxima in PL-lines are close to the interdomain walls in PP-LN, but it is not the case for PP-LT. Possible practical applications are discussed.