BaYF₅:Yb³⁺,Tm³⁺ Upconverting Nanoparticles with Improved Population of the Visible and Near-Infrared Emitting States: Implications for Bioimaging

Abstract

The necessity to enhance specific emissions in lanthanide-doped upconverting nanomaterials in view of a specific application is particularly challenging when Tm3+ is used as a dopant ion due to the plethora of possible cross-relaxation mechanisms. By exploring a host material with a greater Tm3+–Tm3+ interionic distance, it is possible to improve the population of the lower-energy 1G4, 3F2,3, and 3H4 emitting states. The longer Tm3+–Tm3+ interionic distance in cubic Ba1–x Y x F2+x reduces cross-relaxation mechanisms between Tm3+ ions, which results in less probable population of the high-energy Tm3+ levels and weak UV luminescence. Using a thermal decomposition synthesis, nanoparticles are proven to crystallize in the cubic Ba1–x Y x F2+x phase in a CaF2-related structure. Nanoparticles of best quality were obtained for the composition BaYF5 (when x = 0.5), with a cubic lattice parameter a = 5.9073(3) Å. The upconversion mechanisms of BaYF5: Yb3+, Tm3+ nanoparticles are investigated by varying the dopant concentration and characterized by luminescence spectra and decay time measurements. These results prove the absence of the population of the 1D2 level, thus favoring the lower-energy transitions. Quantum yield results also show improved efficiencies of the lower-energy emissions, compared to previously reported results on larger Tm3+ emitting nanoparticles. In summary, using BaYF5: Yb3+, Tm3+ represents a successful strategy to improve the emissions from the lower-energy states, which is advantageous for bioimaging applications that rely on these transitions.

Cation-Ligand Complexation Mediates the Temporal Evolution of Colloidal Fluoride Nanocrystals through Transient Aggregation

“…Because of their unique physical, chemical, and electronic properties, colloidal inorganic fluoride nanocrystals (NCs), namely, nanofluorides, have found applications over the last two decades as functional materials in a variety of fields, including photonics, bioimaging, biomedicine, sensing, catalysis, and more. A case in point are colloidal CaF 2 , which were developed for upconversion fluorescence, time-resolved luminescent, antifungal coating, in vivo magnetic resonance imaging (MRI), − prodrug activation, photodynamic therapy, remineralization of dental caries, and in situ NMR studies .…”

Multi-Mode Lanthanide-Doped Ratiometric Luminescent Nanothermometer for Near-Infrared Imaging within Biological Windows

“…The diffraction peak of the Ba 2 LuF 7 @Ba 2 LaF 7 nanoparticles was slightly offset from the Ba 2 LaF 7 (PDF # 49-0099), which was due to the substitution of La 3+ ions by Lu 3+ ions in the lattice position, forming the cubic phase Ba 2 LuF 7 . For the sake of deeply comprehending the impact of the Yb 3+ /Nd 3+ /Er 3+ ions doping on the crystal structure of the studied samples, the Rietveld refinements of the typical Ba 2 LuF 7 : Yb 3+ /Nd 3+ /Er 3+ @Ba 2 LaF 7 nanoparticles based on their XRD data were carried, as depicted in Figure 1 f. As expected, these calculated diffraction bands were identical to those of the experimental data, which implied that the resultant nanoparticles exhibited a pure cubic phase [ 32 ]. As shown on the upper right in Figure 1 c, the high-resolution TEM image consisted of clear lattice fringes with a spacing of around 0.213 nm.…”

Synthesis and emission dynamics of ultrasmall (sub-3 nm) UCNPs containing a reduced number of emitters

“…Time constants are provided in Table 3. From the simplified Diecke diagram (Figure 7A), 59,60 a kinetic equation for the decay of the population of the 1 D2 state can be derived, neglecting Tm 3+ -to-Yb 3+ back energy transfer (this assumption is justified as the increase of Yb concentration does not imply a decrease of 1 D2 lifetime under UV irradiation, Table 3):…”