The impact of shell host (NaYF₄/CaF₂) and shell deposition methods on the up-conversion enhancement in Tb³⁺, Yb³⁺codoped colloidal α-NaYF₄core–shell nanoparticles

Abstract

Lanthanide doped, up-converting nanoparticles have found considerable interest as luminescent probes in the field of bio-detection. Although the nanoparticles (NPs) have already been successfully applied for fluorescent bio-imaging and bio-assays, the efficiency of the up-conversion process seems to be the bottle-neck in rigorous applications. In this work, we have shown enhancement of the up-conversion in colloidal α-NaYF₄:Yb(3+), Tb(3+) doped nanocrystals owing to passivation of their surface. We have studied quantitatively the influence of the shell type (NaYF₄ and CaF₂), its thickness, as well as the shell deposition method (i.e. single thick shell vs. multi-layer shell) on the luminescent properties of the nanoparticles. The results showed that up to 40-fold up-conversion intensity enhancement may be obtained for the core-shell nanoparticles in comparison with the bare core nanoparticles, irrespective of the shell type and deposition method. Moreover, the suitability of the NaYF₄:Yb(3+), Tb(3+) core-shell NPs for multi-color emission and spectral multiplexing has been presented.

Revisiting the classification of NIR-absorbing/emitting nanomaterials for in vivo bioapplications

“…Examples of such novel possibilities include broadening the temperature sensitivity range of nanothermometers (Figure 11d) 160 or generating different spectral features from unusual lanthanide activators (for example, Tb 3+ emitting at 540 and 580 nm and Eu 3+ at 580 and 620 nm- Figure 11e), thus enabling the creation of more individual spectral signatures for multiple labeling. 161,162 Although the lanthanide-based UC mechanism is more efficient than other anti-Stokes phenomena, this anti-Stokes NIR-to-VIS/NIR is not very efficient in absolute terms. 163 This is especially true for NPs where both the sensitizer and activator ions are susceptible to surface quenching.…”

The effect of intentional potassium co-doping on the luminescent properties of Yb3+ and Tm3+ doped α-NaYF4 core and core–shell nanoparticles

“…the ones modifying crystallographic structure, e.g. Li þ , Ca 2 þ , Sr 2 þ ) ions or intentionally designed core-shell architectures of nanocrystals [9][10][11][12][13][14][15]. For instance, the influence of Ca 2 þ and Sr 2 þ ions on the structure, size and luminescent properties of hexagonal NaYF 4 :Yb 3 þ Er 3 þ disclosed new way to tune the properties of up-converting materials [11].…”

Modulation of the up-converting optical properties of Yb3+/Tm3+ doped α-NaYF4 nanocrystals with calcium co-doping

“…The much lower quantum efficiency of up-conversion (UC) process in lanthanide doped nanomaterials as compared to their bulk counterparts has led to devising many different approaches towards UC luminescence improvement such as selection of appropriate low phonon matrices, minimizing concentration quenching by optimizing activators concentration [1,2], diminishing nanoparticle's surface quenching by employing core-shell designs [3,4], synthesizing hybrid material with plasmon enhanced up-conversion luminescence [5,6] and doping with variety of passive ions [7][8][9].…”