Confining excitation energy of Er3+-sensitized upconversion nanoparticles through introducing various energy trapping centers

Abstract

Luminescence concentration quenching significantly limits the upconversion (UC) performance of lanthanide-doped luminescent materials. Efficient confinement of the excitation energy in a lanthanide activator can alleviate the concentration quenching caused by cross-relaxation and energy migration to surface defects. In this work, a series of new energy trapping centers with varied migrating energy levels (²F_5/2 of Yb³⁺, ³H₅ of Tm³⁺, ⁵I₆ of Ho³⁺, ⁷F₆ of Eu³⁺, and ³F₃ of Pr³⁺etc.) are introduced into NaErF₄@NaYF₄ nanoparticles. The results show that a great enhancement in Er³⁺ UC processes of converting multi-band NIR photons into visible emissions is achieved in NaErF₄@NaYF₄ after adding energy trapping centers. The energy level compatibility between Er³⁺ activators and the energy trapping centers determines the excitation energy confinement, energy-back-transfer efficiency and luminescence output. By incorporating the energy trapping center doped upconversion nanoparticles (UCNPs) into the TiO₂ photoanode of dye-sensitized solar cells (DSSCs), the photon–electron conversion efficiency of DSSCs increases from 6.82% to 7.86% due to the improved multi-band NIR photon harvest of the TiO₂ photoanode with NaErF₄: 10% Yb@NaYF₄.