Effect on photoluminescence, mechanical and structural properties of various rare-earth doped NaNbO3 for optoelectronic applications.

This study investigates the synthesis and characterization of four different rare earth doped NaNb0.995RE0.005O3-δ (RE3+ = Pr3+, Sm3+, Eu3+, and Dy3+) ceramics prepared via a solid-state reaction process. The orthorhombic crystal structure with the Pbcm space group is observed with Pr3+, Sm3+, and Eu3+ doped samples, whereas Dy3+ substitution results in a symmetry modification to a different orthorhombic structure with Pbma symmetry. Raman spectroscopy verified the presence of oxygen vacancies and confirmed that the variation in electronegativity leads to increased broadening and a red shift in the Raman bands. UV-vis-NIR spectroscopy revealed a significant reduction in the band gap from 3.49 to 3.42 eV with reduced dopant ionic radii. Photoluminescence (PL) studies demonstrated that the Sm3+-doped NaNbO3 sample contained various oxygen-vacancy-related bands. The bluish-white to white light region was observed as the ionic radius of the dopants decreased, i.e., Pr3+ > Sm3+ > Eu3+ > Dy3+. The potential of these materials for specialized optoelectronic applications was highlighted by the correlated color temperature (CCT), which was found to be very sensitive to the chemical nature of the dopants and ranged from cold white (6348 K for Sm3+) to cool bluish-white light (8889-8952 K for Pr3+ and Dy3+).