Daniel Liu

Abstract

Luminescence quench is common in overdoped upconversion nanoparticles. Various methods have been proposed to counteract the adverse effects of concentration quenching on luminescence, but in upconversion nanoparticles that are highly doped with both sensitizers and activators, the factors that contribute to the diminishing of the emission cannot be summarized by a single cause. Herein, a core-shell design is used to spatially separate the sensitizer (Yb³⁺) and activator (Er³⁺) and to modulate the emission by changes in the distribution position as well as the concentration of the dopant ions in order to probe the factors affecting the luminescence. When the sensitizer ions are located in the core, the luminescence intensity of the nanoparticles is significantly weaker than that of the other distribution, which implies that the effect of sensitizer and activator on luminescence in the highly doped state has a different and more complex mechanism. The intensity of the emission is more affected by Yb³⁺ than Er³⁺, which includes not only the self-quenching of Yb³⁺, but also the dominance in the Yb³⁺–Er³⁺ cross-relaxation. In this finding may provide new ideas for revealing the reasons for the diminished luminescence of highly doped upconversion nanoparticles and thus for enhancing luminescence.

Publication date: 15 November 2018
Source:Applied Catalysis B: Environmental, Volume 236
Author(s): Ioannis Tamiolakis, Dong Liu, Fang-Xing Xiao, Jian Xie, Ioannis T. Papadas, Teddy Salim, Bin Liu, Qichun Zhang, Stelios A. Choulis, Gerasimos S. Armatas
Band edge engineering of semiconductor nanostructures is one of the most appealing approaches to enhance light absorption, carrier separation and, ultimately, solar to fuel conversion efficiency. In this study, we devise a facile polymer-assisted sol-gel chemical method to prepare highly porous, crystalline implanted SrTiO3 (STO) nanoparticles and demonstrate their performance for photocatalytic hydrogen generation from water. X-ray scattering, electron microscopy, and nitrogen physisorption data corroborate that the as-made catalysts comprise 100-nm-sized nanocuboid particles containing a highly internal porous structure (BET surface area ∼176 m² g⁻¹) with uniform mesopores (ca. 5.8 nm in diameter). Interestingly, a partial substitution of N and C for O is attained in STO lattice with this synthetic protocol, according to the elemental analysis, and infrared (IR) and X-ray photoelectron spectroscopy (XPS) studies. Compared to STO:C,N, the STO:C,N mesoporous decorated with Pt nanoparticles (ca. 3 nm) present unique attributes that allow for an impressive improvement of up to 74-fold in photocatalytic H2-production activity. By combining UV–vis/NIR optical absorption, photoluminescence, Raman and electrochemical impedance spectroscopy, we show that this improved performance arises from the unique nanostructure, which provides massive surface active sites, and the proper alignment of defect states and conduction band-edge position of the STO:C,N semiconductor with respect to the interband transitions of metal, which permit efficient plasmon-induced interfacial electron transfer between the Pt–STO:C,N junction.

Graphical abstract