Influence of Li+ doping on up-conversion and structural properties of Yb3+/Tm3+-doped cubic NaYF4 nanocrystals

• Published in: Journal of luminescence 2014-01, Vol.145, p.956-962
• Main Authors: Misiak, Małgorzata, Cichy, Bartłomiej, Bednarkiewicz, Artur, Stręk, Wiesław
• Format: Article
• Language: English
• Subjects: Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Cubic NaYF4; Emission; Exact sciences and technology; Lattice parameters; Lattices; Li+ co-doping; Lithium ions; Luminescence; Materials science; Nanocrystalline materials; Nanocrystals; Nanoscale materials and structures: fabrication and characterization; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Physics; Quenching; Treatment of materials and its effects on microstructure and properties; Up-conversion luminescence; Upconversion
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/j.jlumin.2013.09.021

The impact of Li+ doping on luminescence and structural properties of cubic NaYF4:Yb3+/Tm3+ colloidal nanocrystals was studied. The Yb3+/Tm3+ co-doped samples demonstrated significant red to blue emission ratio changes and high concentration quenching. By substituting Na+ with smaller Li+ ions within NaYF4 lattice, we expected to induce distortions in order to prevent the concentration quenching process, which is responsible for decrease of the luminescence intensity. The results indicated that the substitution of sodium ions by Li+ did not enhance Tm3+ up-conversion emission significantly in α-NaYF4:Yb3+/Tm3+. However, the influence of lithium ions on luminescence was not entirely the same in the case of 2% Tm3+ and 0.1% Tm3+ doped samples. The slight up-conversion intensity enhancement in the case of samples doped with 2% Tm3+ could result from the increase in the crystallites size and changes in the surface to volume ratio. The observed increase in lattice parameter and thus the increased distance between thulium ions in the lattice might also result in breaking apart of pairs responsible for cross-relaxation processes. Interestingly, in the 0.1% Tm3+ co-doped samples, initial luminescence intensity decrease followed by increase correlated with Li+ substitution was observed. Due to the existence of two different sites for incorporation of lithium ions into the host lattice, the changes in lattice parameters and resulting optical properties are not straightforward functions of variable amount of Li+. •Li+ influence on luminescence of colloidal α-NaYF4:Yb3+/Tm3+ was studied.•The influence of Li+ differed for 2% Tm3+ and 0.1% Tm3+ samples.•UC-luminescence was enhanced with increasing concentration of Li+ in 2% Tm3+ samples.•The luminescence decreased with increasing Li+ concentration in 0.1% Tm3+ samples.