Aluminum-gadolinium mixed oxide matrixes doped with optically active lanthanide ions: Potential candidates for biosensing applications

Abstract

The properties of the gadolinium-aluminum-garnet (GAG) crystalline phase allow it to be applied in the medical and technological areas. GAG doping with Eu³⁺, Yb³⁺, and Er³⁺ ions intensifies its spectroscopic properties and paves the way for its use in photovoltaic cells, cancer treatment, and biosensors. In this study, Gd₃Al₅O₁₂ matrixes doped with lanthanide ions were synthesized by the non-hydrolytic sol–gel route, characterized, and spectroscopically evaluated. For the synthesis, precursor aluminum (AlCl₃) and lanthanide (GdCl₃, EuCl₃, YbCl₃, and ErCl₃) salts were employed at 5:3:1:1:10 or 10:3:1:1:10 Al³⁺/Gd³⁺/Eu³⁺/Er³⁺/Yb³⁺ molar ratio. The resulting lanthanide-doped mixed oxide matrixes consisted of a mixture of GdAlO₃ and Gd₃Al₅O₁₂, and the Al³⁺/Gd³⁺ molar ratio influenced phase formation. The effect of the Er³⁺/Yb³⁺ molar ratio (1:10, 1:5, or 1:1) on the spectroscopic properties of the matrixes was assessed. The excitation and emission spectra displayed the typical bands of Eu³⁺ ions. The bands were broadened, which indicated that Eu³⁺ occupied more than one crystallographic site. The emission spectra presented bands due to Gd³⁺ ions in the ultraviolet region. When energy up-conversion was investigated under 980-nm laser, the bands typical of Er³⁺ ions emerged between 550 and 650 nm. Because the lanthanide-doped mixed oxide matrixes synthesized herein have potential application as biosensors, their cytotoxic effects on mammalian cells were tested.