In this work, we report the low-temperature phase transition of sodium niobate (NaNbO 3 ) ceramics at the antiferroelectric-ferroelectric phase studied by the Raman scattering technique over the temperature range 10-300 K. The spectral shape indicates that the phase transition occurs at 160 K on the cooling cycle and at 260 K on heating. The recorded spectra are discussed following the separation of modes into the internal stretching modes of the NbO 6 octahedron and Na + cation translational modes. The 62 and 75 cm −1 peaks are proposed as the translational modes of Na + cation against the NbO 6 octahedron.

Raman studies of crystalline iron perchlorate hexahydrate (Fe(ClO 4 ) 2 ·6H 2 O) in the region of lattice and anion internal modes were carried out in the temperature range 80-385 K. The temperature-dependent Raman results are consistent with those from previous works, showing that two phase transitions occur around 336 and 245 K. The transition at 336 K may be considered as an order-disorder transformation, while the one at 245 K is associated with the configurational disorder of the tetrahedron of the perchlorate ions.

This work studies the two-photon luminescence spectra of a Yb3+doped YAG crystal grown using the Czochralski method. To study the spectral performance of a 50 at.% Yb:YAG crystal, intense green light (centered at about 544nm) was generated by the crystal upon excitation using a 973nm InGaAs LD pump source. The luminescence spectra were obtained for various Yb concentrations and the emission intensity were plotted versus Yb3+concentration. The green emission light attributed to Yb3+two-photon transition.