Investigation of Upconversion Photoluminescence of Yb3+/Er3+:NaLaMgWO6 Noncytotoxic Double-Perovskite Nanophosphors

Bright fluorescent rare-earth-ion-doped upconversion nanomaterials are attractive choices for photonic devices. A remarkable green upconversion emission has been obtained by the sensitizing effect of Yb³⁺ in a Yb³⁺/Er³⁺:NaLaMgWO₆ (NLMWO) nanophosphor under near-infrared (NIR) excitation. A citrate sol-gel method was employed to synthesize the nanophosphor samples. The lack of a secondary phase in the X-ray diffraction pattern confirms that the Er³⁺ and Yb³⁺ ions are incorporated in the ordered double-perovskite structure. Surface analysis and particle evaluation are performed by field-emission scanning electron microscopy and transmission electron microscopy analysis. Upconversion and downconversion emission performances were systematically studied by varying the dopant concentrations. A strong upconversion green emission can be observed with the naked eye, and it resembles the upconversion spectra of Er³⁺-doped phosphors. Remarkably, because of an energy-transfer process, the green upconversion emission can be converted into a strong red emission by codoping with Yb³⁺ ions. We observed the color tuning effect from green to red, which can be controlled by varying the Yb³⁺ concentration in the codoped phosphors during NIR excitation. A systematic investigation of the upconversion mechanism from Yb³⁺ to Er³⁺ doubly doped NLMWO nanocrystals is demonstrated. The upconversion mechanism was evaluated only by varying the excitation power of the laser as well. A strong NIR emission at 1.57 μm corresponding to Er³⁺ can be significantly enhanced by increasing the codoping concentration of Yb³⁺ ions. The energy migration pathway is accurately presented. The Commission internationale de l'éclairage color coordinates were analyzed for singly and doubly doped nanophosphors. The cytotoxicity of the codoped nanophosphor system was evaluated using WI-38 cell lines. This optimized codoped nanophosphor material is noncytotoxic; thus, it can be useful for in vitro studies in biological studies. On the basis of the obtained results, the NLMWO:Yb³⁺/Er³⁺ nanophosphors can be a promising choice for novel upconversion photonic applications.