Enhanced near infrared-to-visible upconversion in the CaTiO3:Yb3+/Er3+ phosphor via the host lattice modification using co-doping of Mg2+ ions

Abstract

The CaTiO₃:Er³⁺/Yb³⁺ upconversion phosphor was synthesized using a simplified co-precipitation method and the effect of Mg²⁺ ion co-doping was investigated on the structural and optical properties focusing on the near-infrared (NIR)-to-visible upconversion. The introduction of Mg²⁺ ions into the host lattice produced substantial changes in the crystal structure, grain size, and absorption, thus leading to the enhancement in upconversion emission intensities. X-ray diffraction (XRD) analysis indicated the formation of polycrystalline CaTiO₃–Ca₄Ti₃O₁₀ composite crystals and an increase in the crystallite size was observed upon increasing the Mg²⁺ ion concentration in the samples. Elemental analysis by energy dispersive spectroscopy (EDS) suggested the substitution of Ca²⁺ ions by Mg²⁺ ions in the CaTiO₃ host lattice. Moreover, a change in the Yb³⁺/Er³⁺ ratio from 0.25 to 1.1 indicated the redistribution of the Er³⁺ or Yb³⁺ ions caused by the Mg²⁺ ions. These lattice deformations further resulted in an improved absorption of Er³⁺ ions, exhibiting a ∼3-fold enhancement in the upconversion emission intensity (at the excitation intensity of ∼1 W cm⁻²).