Upconversion luminescence with tunable lifetime in NaYF₄:Yb,Er nanocrystals: role of nanocrystal size

Abstract

Despite recent achievements to reduce surface quenching in NaYF(4):Yb,Er nanocrystals, a complete understanding of how the nanocrystal size affects the brightness of upconversion luminescence is still incomplete. Here we investigated upconversion luminescence of Yb,Er-doped nanocrystals in a broad range of sizes from 6 nm to 45 nm (cubic or hexagonal phases), displaying an increasing red-to-green luminescence intensity ratio and reduced luminescence lifetimes with decreasing size. By analyzing the upconversion process with a set of rate equations, we found that their asymptotic analytic solutions explain lower decay rates of red compared to green upconversion luminescence. Furthermore, we quantified the effect of the surface on luminescence lifetime in a model where nanocrystal emitters are divided between the near-surface and inside regions of each nanocrystal. We clarify the influence of the four nonradiative recombination mechanisms (intrinsic phonon modes, vibration energy of surface ligands, solvent-mediated quenching, and surface defects) on the decay rates for different-size nanocrystals, and find that the defect density dominates decay rates for small (below 15 nm) nanocrystals. Our results indicate that a defect-reduction strategy is a key step in producing small upconversion nanocrystals with increased brightness for a variety of bioimaging and biosensing applications.

Precisely Tailoring Upconversion Dynamics via Energy Migration in Core–Shell Nanostructures

“…Note that without the long‐distance energy migration, such a large time span modulation of the rise is hardly achieved in traditional Yb 3+ /Er 3+ co‐doping systems 7e, 9. Importantly, such a tuning effect is well predicted by our simulation model (Figure 3 c, dotted traces).…”

Phase angle encoded upconversion luminescent nanocrystals for multiplexing applications

“…In view of this, we developed a simple method to generate phaseangle encoded UCNPs while maintaining high luminescence intensity, i.e., nanoparticle size adjustment regulated by opticallyinert-ion doping. This method takes advantages of the inherent surface quenching effect for UCNPs, i.e., that the lifetimes of involved states of both the sensitizers and activators are susceptible to environments 43,53,54 . (Fig.…”

“…We initiated the luminescence kinetics-management study by manipulating the homogenously-doped emitting layer by means of the doping concentration effect, given that upconversion luminescence is highly dependent on dopant concentrations 28,43 . A typical core-shell structure, NaYF 4 :x%Yb 3+ ,y%Er 3+ @NaLuF 4 , was concentration in the isolated pumping core on the temporal behaviors of 543 nm upconversion luminescence (Upper) and the resulting phase angles.…”

White-light upconversion emission of lanthanide double-doped oxide nanoparticles via defect state luminescence of ZnO

“…However, the relatively low efficiency of white UCL sources still poses a challenge to researchers today. It is well-known that the efficiency of white UCL is highly dependent on host matrix, particle morphology, crystallite phase, and lanthanide dopants [18][19][20][21][22][23]. Therefore, the study of their host matrix is important for obtaining a good white UCL emission and white light [24].…”