Modifying the size and uniformity of upconversion Yb/Er:NaGdF4 nanocrystals through alkaline-earth doping

Abstract

NaGdF4 is regarded as an ideal upconversion (UC) host material for lanthanide (Ln(3+)) activators because of its unique crystal structure, high Ln(3+) solubility, low phonon energy and high photochemical stability, and Ln(3+)-doped NaGdF4 UC nanocrystals (NCs) have been widely investigated as bio-imaging and magnetic resonance imaging agents recently. To realize their practical applications, controlling the size and uniformity of the monodisperse Ln(3+)-doped NaGdF4 UC NCs is highly desired. Unlike the routine routes by finely adjusting the multiple experimental parameters, herein we provide a facile and straightforward strategy to modify the size and uniformity of NaGdF4 NCs via alkaline-earth doping for the first time. With the increase of alkaline-earth doping content, the size of NaGdF4 NCs increases gradually, while the size-uniformity is still retained. We attribute this "focusing" of size distribution to the diffusion controlled growth of NaGdF4 NCs induced by alkaline-earth doping. Importantly, adopting the Ca(2+)-doped Yb/Er:NaGdF4 NCs as cores, the complete Ca/Yb/Er:NaGdF4@NaYF4 core-shell particles with excellent size-uniformity can be easily achieved. However, when taking the Yb/Er:NaGdF4 NCs without Ca(2+) doping as cores, they could not be perfectly covered by NaYF4 shells, and the obtained products are non-uniform in size. As a result, the UC emission intensity of the complete core-shell NCs increases by about 30 times in comparison with that of the cores, owing to the effective surface passivation of the Ca(2+)-doped cores and therefore protection of Er(3+) in the cores from the non-radiative decay caused by surface defects, whereas the UC intensity of the incomplete core-shell NCs is enhanced by only 3 times.

Simultaneous morphology manipulation and upconversion luminescence enhancement of β-NaYF4:Yb3+/Er3+ microcrystals by simply tuning the KF dosage

“…As shown in Fig. 7a, the characteristic UC emission bands centered at 521 nm, 540 nm and 656 nm can be ascribed to 2 H 11/2  →  4 I 15/2 (green), 4 S 3/2  →  4 I 15/2 (green) and 4 F 9/2  →  4 I 15/2 (red) transitions of Er 3+ , respectively39. It is worth noticing that the UC luminescence intensities in both the green and red regions increase notably with the increment of molar ratio of KF to RE 3+ .…”

Decrease in particle size and enhancement of upconversion emission through Y3+ions doping in hexagonal NaLuF4:Yb3+/Er3+nanocrystals

“…25,26 To explore the local symmetry of as-prepared samples, Eu 3+ ions were taken as the structural probe to investigate the modification of the symmetry of the local crystal field induced by Y 3+ ions doping. Therefore, the intensity ratio of the 5 D 0 → 7 F 2 transition to the 5 D 0 → 7 F 1 transition can act as an efficient fingerprint of local symmetry for a luminescent center.…”

Enhanced temperature sensing response of upconversion luminescence in ZnO–CaTiO3: Er3+/Yb3+ nano-composite phosphor

“…The rare earth ions doped materials are well known for upconversion emission and have drawn much interest since last one decade as many potential applications of these materials in three dimensional displays, lasers, solar cells, photo-dynamic therapy, etc. [4][5][6][7][8][9][10] were suggested. The Er 3+ ion has enough number of long lived energy levels and thus showing strong upconversion emissions in UV-Visible region on infrared excitation.…”