Power-Dependent Optimal Concentrations of Tm³⁺ and Yb³⁺ in Upconversion Nanoparticles

Abstract

Lanthanide-doped upconversion nanoparticles (UCNPs) have enabled a broad range of emerging nanophotonics and biophotonics applications. Here, we provide a quantitative guide to the optimum concentrations of Yb 3+ sensitizer and Tm 3+ emitter ions, highly dependent on the excitation power densities. To achieve this, we fabricate the inert-

Universal Emission Characteristics of Upconverting Nanoparticles Revealed by Single-Particle Spectroscopy

“…The emission intensity proportional to the volume of single particle, which is consistent with those from Yb 3+ ,Er 3+ -doped UCNPs of 2% Er 3+ with different sizes in the photon saturation regime (>1 MW cm −2 ), 5 is now extended to the unsaturated regime. Combining the dependence on volume with the emission intensity proportional to the activator concentration of 2%, 4%, and 8% Tm 3+ in Yb 3+ ,Tm 3+ -doped UCNPs in the saturation regime (>10 MW cm −2 ), 23 we recognize that the emission intensity from a single UCNP is proportional to the number of activators, that is, its volume times activator concentration.…”

“…For a wide range of applications, UCNPs that can achieve high brightness have been pursued via various strategies, including surface passivation using the core–shell structure − or ligand coordination with an inert layer to reduce surface-mediated energy loss, dye sensitization using organic fluorophores , to boost light absorption, and high doping of lanthanide ions under a high excitation power density − to provide sufficient incident photons for upconversion. To reduce the excitation power requirement, the emission intensity as a function of irradiance has been analyzed for various compositions at the ensemble level; ,,− however, this strongly depends on the measurement environment, such as powder or suspension, and the concentration of the UCNPs.…”

“…To reduce the excitation power requirement, the emission intensity as a function of irradiance has been analyzed for various compositions at the ensemble level; ,,− however, this strongly depends on the measurement environment, such as powder or suspension, and the concentration of the UCNPs. Therefore, the irradiance-dependent emission intensity of UCNPs at the single-particle level has been actively investigated to determine the individual features of single particles, mostly using confocal microscopy. ,− Nevertheless, it is difficult to determine the relationship between the number of incident and emitted photons for a single nanoparticle because this relationship is highly dependent not only on the nanoparticle size or nonlinearity-dependent resolution but also on the instrumentation settings, such as the pixel size, pinhole size, and optical alignment in confocal microscopy. Single-particle irradiance-dependent imaging at low irradiance down to 8 W cm –2 has been demonstrated using Yb 3+ ,Er 3+ -doped core–shell–shell structure UCNPs under wide-field illumination .…”

Enhanced two-step two-frequency upconversion luminescence in a core/shell/shell nanostructure

“…The UCNPs were prepared by a solvothermal method 57,58 . The core/shell/shell UCNPs were prepared by layer-by-layer epitaxial growth method 59,60 . NaYF 4 :0.5%Er UCNPs were first prepared and then covered by NaGdF 4 :2%Yb and NaYF 4 :1%Er shell gradually (Figure 2).…”

An overview of boosting lanthanide upconversion luminescence through chemical methods and physical strategies

“…These include core-shell structure design, dye sensitization and high-density power excitation, which are highly desirable for breaking the dopant thresholds of Yb 3+ , Er 3+ , Tm 3+ and Nd 3+ ions. [34][35][36] In order to avoid repetitive discussion, we here skip over cases exemplifying these strategies, which will be discussed in detail in subsequent sections (see section 2.2, 2.4 and 3.1.1).…”