Upconversion Luminescence Properties of Gd₂O₃: Er³⁺ Nanospheres and Gd₂O₃: Er³⁺@Silica Nanocomposites

Abstract

The upconversion luminescence (UCL) of Gd₂O₃: Er³⁺ monodisperse nanospheres, synthesized by multistep chemical method, and nanoparticles, produced by combustion synthesis, are presented for comparison. The UCL of nanospheres Gd₂O₃: Er³⁺ and Gd₂O₃: Er³⁺@Silica have shown strong red or green emission under excitation at 976 nm or 980 nm by a diode laser with a remarkable increase of the bright red color in the nanospheres. In the core/shell structured nanospheres Gd₂O₃: Er³⁺@Silica, we find a higher intensity of upcoversion emission, increased stability and better dispersion capability in solvents and water. The UCL intensities of green and red color while 976 nm or 980 nm excitation were dependent on the diode laser power. The slope values of Er³⁺ ion’s transitions ²H_11/2–⁴I_15/2, ⁴S_3/2–⁴I_15/2 and ⁴F_9/2–⁴I_15/2 in the silica-coated nanospheres are 1.99, 1.62 and 1.66 respectively, which properly indicate the two-photon mechanism of upconversion emission. The synthesized Gd₂O₃ nanospheres codoped with Yb and Er show strong UCL intensity than those of Gd₂O₃: Er³⁺. The obtained Gd₂O₃: Er³⁺ nanospheres and nanoparticles, as well as Gd₂O₃: Yb³⁺, Er³⁺ and its silica-coated versions, are promising materials to develop with potential application in high technology and biomedicine.

HRTEM image of nanospheres Gd₂O₃: Yb³⁺ 18%, Er³⁺ 2.0%. @Silica after heating at 650°C (a); TEM image of Gd₂O₃:Er³⁺ 2.0%@ Silica after heating at 650°C (b); UCL spectra of Gd₂O₃:2.0%Er@silica, λ_exc 980 nm excited powers of 105, 260 and 400 mW (c); Log UCL band of Gd₂O₃:Er³⁺2.0%@Silica versus Log laser pump power (λ_exc 980 nm) (d).