Effects of doping and epitaxy on optical behavior of NaNbO3 films

Abstract

Cube-on-cube epitaxy of perovskite sub-cell of Pr-doped and undoped NaNbO3 is obtained in 130-nm-thick films on top of (La0.18Sr0.82)(Al0.59Ta0.41)O3 (001) substrates. Experimental studies show that the edge of optical absorption red-shifts and some interband transitions change in the films compared to crystals. Bright red luminescence is achieved at room-temperature under ultraviolet excitation in the Pr-doped film. An interband mechanism of luminescence excitation is detected in the film, which is in contrast to the intervalence charge transfer mechanism in the crystal. The results are discussed in terms of epitaxially induced changes of crystal symmetry and ferroelectric polarization in the films. It is suggested that the band structure and interband transitions in NaNbO3 and the transition probabilities in the Pr ions can be significantly modified by these changes.