Niobium oxide influence on the structural properties and NIR luminescence of Er3+/Yb3+ co-doped and single-doped 1−xSiO2−xNb2O5 nanocomposites prepared by an alternative sol–gel route

• Published in: Journal of luminescence 2016-12, Vol.180, p.355-363
• Main Authors: Caixeta, Fábio José, Aquino, Felipe Thomaz, Pereira, Rafael Ramiro, Gonçalves, Rogéria Rocha
• Format: Article
• Language: English
• Subjects: Niobium(V) oxide; NIR emission; Photoluminescence; Rare earth; Sol–gel
• ISSN: 0022-2313
• DOI: 10.1016/j.jlumin.2016.08.057

We have investigated how the Nb content influences the structural and luminescence properties of Er3+/Yb3+ co-doped SiO2–Nb2O5 nanocomposites prepared by an alternative sol-gel process at different Si/Nb molar ratios of 90:10 up to 20:80. X-ray diffraction (XRD), Transmission electron microscopy (TEM), Diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), and Photoluminescence spectroscopy (PL) provided a detailed structural and spectroscopic analysis of the composites. Formation of the Nb2O5 crystalline phases depended on the Si/Nb ratio. Nanocomposites with 20 up to 40 and 80mol% of Nb contained the T crystalline phase, whereas nanocomposites with 50mol% of Nb presented both the T and M crystalline phases. The average crystallite size increased from 5.9nm to 33.8nm as the niobium content, as revealed by XRD. The λcutoff increased with the Nb content, and the band gap energy ranged from 4.27eV to 3.54eV. Full elimination of OH groups was suitable for the highest Nb concentrations, which influenced the luminescence properties. Efficient Yb3+ → Er3+ energy transfer occurred under 977-nm excitation, leading to broad and intense 1.5-µm emission for Nb30 and Nb40, with FWHM of 67nm and 69nm, respectively. Under 520-nm and host excitations, Er3+ and Yb3+ emissions at 1.0µm took place. The different Nb2O5 crystalline phases influenced the energy transfer processes between Er3+ and Yb3+ ions, which affected the relative intensity of the 1.0/1.5-μm emissions. Tuning of this relative intensity is possible depending on the Nb content, which paves the way for the application of these nanocomposites as optical amplifiers at 1.5μm, solid-state lasers and energy converters. The Er3+/Yb3+ co-doped nanocomposites with 30 and 40mol% of Nb amount displayed the most promising luminescence properties for photonic applications.