Simultaneous Realization of Phase/Size Manipulation, Upconversion Luminescence Enhancement, and Blood Vessel Imaging in Multifunctional Nanoprobes Through Transition Metal Mn²⁺ Doping

Abstract

A strategy is demonstrated for simultaneous phase/size manipulation, multicolor tuning, and remarkably enhanced upconversion luminescence (UCL), particularly in red emission bands in fi xed formulae of general lanthanidedoped upconverting nanoparticles (UCNPs), namely NaLnF 4 :Yb/Er (Ln: Lu, Gd, Yb), simply through transition metal Mn 2+ -doping. The addition of different Mn 2+ dopant contents in NaLnF 4 :Yb/Er system favors the crystal structure changing from hexagonal (β) phase to cubic (α) phase, and the crystal size of UCNPs can be effectively controlled. Moreover, the UCL can be tuned from green through yellow and to dominant red emissions under the excitation of 980 nm laser. Interestingly, a large enhancement in overall UCL spectra of Mn 2+ doped UCNPs (∼59.1 times for NaLuF 4 host, ∼39.3 times for NaYbF 4 host compared to the UCNPs without Mn 2+ doping) is observed, mainly due to remarkably enhanced luminescence in the red band. The obtained result greatly benefi ts in vitro and in vivo upconversion bioimaging with highly sensitive and deeper tissue penetration. To prove the application, a select sample of nanocrystal is used as an optical probe for in vitro cell and in vivo bioimaging to verify the merits of high contrast, deeper tissue penetration, and the absence of autofl uorescence. Furthermore, the blood vessel of lung of a nude mouse with the injection of Mn 2+ -doped NaLuF 4 : Yb/ Er UCNPs can be readily visualized using X-ray imaging. Therefore, the Mn 2+ doping method provides a new strategy for phase/size control, multicolor tuning, and remarkable enhancement of UCL dominated by red emission, which will impact on the fi eld of bioimaging based on UCNP nanoprobes.

Selectively enhanced red upconversion luminescence and phase/size manipulation via Fe 3+ doping in NaYF 4 :Yb,Er nanocrystals

“…These results indicate that the phase and size of NaYF 4 : Yb,Er can be conveniently manipulated via adjusting the doped Fe 3+ contents. The crystalline size increases firstly as in Fe 3+ -free to 10 mol% Fe 3+ samples and decreases subsequently when Fe 3+ is further introduced up to 40 mol%, which is quite different from the literature, 23 in which smaller size Mn 2+ ions doped into NaLuF 4 nanocrystals can induce a continuous growth of the particles. It is natural and rational to understand the size increase upon Fe 3+ codoping by the formation of transient electric dipoles originated from smaller substitution ions for larger ions in the host lattice, which can accelerate the diffusion of F − from the solution to the grain therefore enlarge the nanoparticles.…”

“…1(a)). There shows an apparent discrepancy between the results herein and the literature, 23,28 in which it is generally believed that introducing dopants with smaller radii compared to the substituted ions in the host lattice could induce hexagonal-to-cubic phase transformation. To understand this "anomalous" discrepancy, we propose that it is not the size itself but the size difference between the dopants and substituted ions in the host lattice that functions the phase manipulation mechanism.…”

Low-temperature open-air synthesis of PVP-coated NaYF 4 :Yb,Er,Mn upconversion nanoparticles with strong red emission

“…This trend was reflected in a shift towards higher 2θ angles for all samples between 0 and 35 mol% Mn 2+ , with a similar reversal for 40% Mn 2+ (see electronic supplementary material, figure S8c,d,f,g,h). Similar shifts in 2θ angle have been reported for upconversion materials co-doped with Fe 3+ and Mn 2+ [55,[57][58][59][60].…”

Multicolor tuning towards single red-emission band of upconversion nanoparticles for tunable optical component and optical/x-ray imaging agents via Ce3+ doping

“…Liu and his co-workers [33] successfully obtained UC emissions from blue to NIR based on Ln 3+ -doped NaYF 4 UCNPs, demonstrating that the R/G ratio was highly enhanced by increasing the doped Yb 3+ concentration in a Yb 3+ /Er 3+ codoped NaYF 4 system. As reported in Zhao's and our previous reports [34,35], tunable multicolor and remarkably enhanced red emission can be realized in NaLnF 4 :Yb 3+ /Er 3+ (Ln 3+ =Y 3+ , Lu 3+ , Gd 3+ , and Yb 3+ ) UCNPs by Mn 2+ doping, where Mn 2+ substituted at the sites of Ln 3+ in the host lattice. In addition, single-band red emission can be obtained from Yb 3+ /Er 3+ (Ho 3+ ) co-doped KMnF 3 UCNPs [36].…”