Synthesis and Upconversion Luminescence of Gd2O3:Yb3+, Er3+, Tm3+ and Gd2O2S:Yb3+, Er3+, Tm3+ Compounds

Abstract

The synthesis and upconversion properties of Gd₂O₃:Yb³⁺, Er³⁺, Tm³⁺ oxide and Gd₂O₂S:Yb³⁺, Er³⁺, Tm³⁺ oxysulfide are the subjects of study in this paper. The aim of the work is to develop a method for synthesizing phosphors by sulfiding (temperature 900°C, 4 h) Gd₂O₃:Yb³⁺, Er³⁺, Tm³⁺ oxide obtained by the hydrothermal method with subsequent calcination at 900°C, with morphological certification of the particles, and to study the upconversion properties of the oxide and oxysulfide. The distribution of elements in the obtained samples was analyzed using the method of energy-dispersive X-ray spectroscopy. The chemical composition was confirmed by inductively coupled plasma atomic emission spectroscopy. The results of refinement of the crystal parameters of the oxysulfide using the Rietveld method are P\(\bar {3}\)m1, a = 3.8529(5) Å, c = 6.6659(1) Å, V = 86.15 ų. The upconversion luminescence of the Gd₂O₃:Yb³⁺, Er³⁺, Tm³⁺ oxide and the Gd₂O₂S:Yb³⁺, Er³⁺, Tm³⁺ oxysulfide is caused by energy transfer from the ytterbium ions to the thulium and erbium ions and the subsequent radiative transitions ¹G₄ → ³H₆, ³F_2,3 → ³H₆, ³H₄ → ³H₆ of the Tm³⁺ ion and ²H_11/2/⁴S_3/2 → ⁴I1_5/2, ⁴F_9/2 → ⁴I_15/2 of the Er³⁺ ion. A two-photon upconversion mechanism in the green, red, and near-IR spectral regions was identified based on the results of measuring the luminescence intensity of the oxide and oxysulfide. The color coordinates according to the CIE chromaticity diagram of Gd₂O₃:Yb³⁺, Er³⁺, Tm³⁺ and Gd₂O₂S:Yb³⁺, Er³⁺, Tm³⁺ correspond to orange and yellow-green emission, respectively. It is concluded in the paper that the synthesis ensures efficient upconversion and controlled emission, which is confirmed by spectra and morphology. Biological labeling and visualization are the fields of application of the results.