Upconversion improvement by the reduction of Na⁺-vacancies in Mn²⁺ doped hexagonal NaYbF₄:Er³⁺ nanoparticles

Abstract

Hexagonal-phase NaYbF4:Er(3+) upconversion nanoparticles (UCNPs) have been synthesized via a co-precipitation method in high-boiling-point solvents, and remarkably enhanced upconversion luminescence, particularly in red emission bands (650-670 nm) in NaYbF4:Er(3+) UCNPs, has been achieved by Mn(2+) doping. The underlying reason for luminescence enhancement by Mn(2+) doping is explored by a series of controlled experiments, and a mechanism of enhancement based on the decrease of Na(+)-vacancies and organic adsorption is proposed. The Mn(2+) substitution disturbs the equilibrium of the charge and crystal lattice in the hexagonal-phase NaYbF4:Er(3+) UCNPs, which makes the Na(+)-vacancies that quenched luminescence become filled with Na(+) or Mn(2+) to offset the imbalance of the charge and electron cloud distortion. In addition, the Mn(2+) doping at the surface of UCNPs could reduce the organic adsorption on the surface of the UCNPs by an extra F(-) ion on the grain surface resulting in luminescence enhancement. Therefore, the Mn(2+)-doping approach provides a facile strategy for improvement of luminescence, which will impact on the field of bioimaging based on UCNP nanoprobes.

Synthesis of a novel bifunctional nanocomposite with tunable upconversion emission and magnetic properties

“…18 Tian's group found the total luminescence intensity of NaYbF 4 :Er 3+ UCNPs doped with 20 mol% Mn 2+ ions is about 20 times higher than that of NaYbF 4 :Er 3+ UCNPs doped without Mn 2+ ions. 19 J. Kim doped 30 mol% Fe 3+ in NaGdF 4 :Yb, Er nanocrystals and observed enhancement up to 34 and 30 times in the visible green and red UC emissions. 20 All of the above results show that transition metal ions doping into the host lattice can modify the optical and magnetic properties.…”

Time-Gated Imaging of Latent Fingerprints with Level 3 Details Achieved by Persistent Luminescent Fluoride Nanoparticles

“…These positively charged V F • might adsorb free F – ions in the solution and form a negatively electrostatic layer to hinder further diffusion of F – ions toward the surface during nanoparticle growth. , The XPS spectra demonstrated that Mn dominantly existed in the valence state of Mn 2+ (Figure c,d). The high-resolution details of the binding energies for the 2p 1/2 (652.1 eV) and 2p 3/2 levels (639.6 eV) of Mn 2+ were consistent with the literature. , …”

Upconversion Composite Nanoparticles for Tumor Hypoxia Modulation and Enhanced Near-Infrared-Triggered Photodynamic Therapy

“…In C@S, Yb 3+ , doping would cause the increase of the lattice space in the CaF 2 crystal. Subsequently, when Mn 2+ ions were incorporated into the lattice, Mn 2+ ions may possibly act as the interstitial atoms in the lattice of CaF 2 nanocrystals at the initial stage when the low amount of Mn 2+ ions are diffused and then occupy Yb 3+ sites as the further increase of Mn 2+ doping. , The existence of Mn 2+ disturbs the transition possibilities between green and red emissions of Er 3+ and facilitates the dominate occurrence of red emission, resulting in an emission color output from green to red by ratio controlling of the Mn 2+ doping level (Figure S3). Besides influencing the lattice distortion by Mn 2+ doping, quenching of UCL emission by MnO 2 would occur with the coating of the MnO 2 shell.…”