Crystal Growth of a New Series of Complex Niobates, LnKNaNbO5 (Ln = La, Pr, Nd, Sm, Eu, Gd, and Tb): Structural Properties and Photoluminescence

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Single crystals of LnKNaNbO5 (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb) were grown out of a reactive high temperature hydroxide melt. The structures were solved by single crystal X-ray diffraction. All compounds of the series LnKNaNbO5 crystallize in the space group P4/nmm. The niobium is located in a rare square pyramidal coordination environment in this layered structure. EuKNaNbO5, GdKNaNbO5, and TbKNaNbO5 exhibit room temperature photoluminescence with bright orange-red, pink-purple, and green emissions, respectively. Unlike in many oxide structures, the photoluminescence is not quenched, although the rare earth elements fully occupy a position in the crystal structure.