Self-sensitization induced upconversion of Er³⁺ in core–shell nanoparticles

Abstract

A mechanistic study of upconversion from lanthanides is of great importance for the fundamental research of upconversion materials and their diverse frontier applications. However, the most efficient upconversion of lanthanides is still obtained in a commonly used sensitizer-activator coupled system. Here we report a mechanistic investigation on the upconversion of Er3+ through self-sensitization which is applicable for 808, 980 and 1530 nm excitations. It is found that the cooperative energy transfer upconversion followed by cross-relaxation occurring among Er3+ ions plays a critical role in producing and enhancing the red upconversion for the samples with high dopant concentrations (e.g., >20 mol%). The red upconversion color can be further purified and enhanced by mediating the upconversion dynamics through introducing the lanthanides of Ho3+, Tm3+ and Yb3+, which can effectively contribute to the population in the red emitting state. Moreover, the energy migration in the Er-sublattice was also found to be a possible origin for quenching upconversion, which was proved and effectively suppressed by designing a tri-layered nanostructure where the distribution of Er3+ is spatially controllable. Our results gain access into the insight of upconversion dynamics in self-sensitization induced upconversion which would help the search for other new kinds of upconversion materials.

Dual-Wavelength Excited Intense Red Upconversion Luminescence from Er3+-Sensitized Y2O3 Nanocrystals Fabricated by Spray Flame Synthesis

“…To meet diverse application needs, great efforts have been done to find new sensitizers with multiple effective excitation wavelengths. With the recent 808 and 980 nm lasers showing efficient excitations, Er 3+ sensitizers have become promising candidates [ 13 , 14 , 15 ]. For instance, under the excitation of 980 nm laser, the various emission wavelengths of Er 3+ -sensitized UCNPs provide the ability of multicolor tuning from green to red, which is important for anticounterfeiting and multiplexed labeling applications [ 4 ].…”

NIR‐II/III Luminescence Ratiometric Nanothermometry with Phonon‐Tuned Sensitivity

“…This conclusion is further supported by the observation of the decrease of 1545 nm emission when increasing Ho 3+ doping concentration from 1% to 1.5%. An enhancement of 1545 nm emission was observed when increasing Ho 3+ from 1.5% to 2%, implying the existence of another PAT from the 5 I 6 of Ho 3+ back to the 4 I 13/2 of Er 3+ that can well explain Ho 3+ ‐concentration‐dependent 1545 nm emission decay profiles (Figure S6, Supporting Information) . Measured I 1545 /I 1194 (LIR) was plotted versus temperature in Figure g and Figure S7 (Supporting Information), and fitted with Equation that involves a phonon mode.…”

Understanding the Role of Yb3+ in the Nd/Yb Coupled 808-nm-Responsive Upconversion

“…Note that this Yb 3+ content (50 mol%) in the interlayer is much higher than that from the NaYF 4 :Yb/Er@NaYF 4 :Nd/Yb core-shell nanostructure (10 mol%), revealing that there might exist a possibility of energy migration over to the surface which can quench the upconversion. In this case, the designs with high doping of migratory lanthanides need an optically inert shell layer to isolate the interactions between lanthanide emitter and surface quencher (Liu et al, 2018; Yan et al, 2018). Notably, the upconversion emission intensity is much weaker for these samples without the outermost shell layer (Figure S6).…”