Passivation of lanthanide surface sites in sub-10 nm NaYF4:Eu3+ nanocrystals

Abstract

We examined in detail the optical properties of NaYF4:Eu3+ nanocrystals of ~9 nm in diameter. For such small nanocrystals roughly 17 % of Y3+ ions occupy surface sites and can be efficiently substituted by optically active Eu3+ ions. In order to determine the influence of surface Eu3+ on the optical properties of the whole nanocrystal, small β-NaYF4:Eu3+ nanocrystals with homogenous size distribution were prepared using trioctylphosphine oxide as a coordinating solvent. In order to passivate the surface sites, a thin β-NaYF4 shell was further deposited on nanocrystals core and the optical properties were investigated. For this purpose absorption, photoluminescence, photoluminescence excitation, and photoluminescence decays were recorded and analyzed. The optical characteristics of surface Eu3+ significantly diminish for surface passivated nanocrystals. We calculated the increase of quantum yield to the value of 64 % when NaYF4:Eu3+ core was capped by undoped shell. The optical spectroscopy techniques were shown to be sufficient in determination of surface passivation of nanocrystals with high surface to volume ratio.

Rapid Synthesis of Sub‐10 nm Hexagonal NaYF4‐Based Upconverting Nanoparticles using Therminol® 66

“…Thisr esults in manipulated host lattices, which has ad etrimentale ffect on the luminescent properties of the final materials. [25][26][27][28][29] Other popular strategiest oo btain sub-10 nm UCNPs involve the use of an additional high-boiling solvent such as oleylamine (OM) [30] or trioctylphosphine oxide (TOPO) [31][32][33][34] in the reaction formulation under harsh synthesis conditions (high temperatures and long reaction times), which limits the choice of compatible solvent systemsthat can be used.…”

Triluminescent Functional Composite Pigment for Non‐Replicable Security Codes to Combat Counterfeiting

“…The downshift PL excitation and emission spectra of the triluminescent functional composite pigment are shown in Figure c, d. The obtained excitation spectrum exhibits the broad peak at 210–260 nm centered at 254 nm as well as some other peaks between 320–500 nm at fixed emission of 609 nm, as shown in Figure c. The broad peak originates due to the charge transfer state (CTS), and the other peaks arise from f‐f transitions within the 4f 6 electron shell of Eu 3+ ion . The peaks originated due to the f‐f transitions are corresponding to 7 F 0 (ground state) to different excited states: 5 H 0 (321 nm), 5 D 4 (362 nm), 5 G 2 (381 nm), 5 L 6 (393 nm), 5 D 3 (414 nm) and 5 D 2 (466 nm).…”

“…The broad peak originates due to the charge transfer state (CTS), and the other peaks arise from f-f transitions within the 4f 6 electron shell of Eu 3 + ion. [28] The peaks originated due to the f-f transitions are corresponding to 7 F 0 (ground state) to different excited states: 5 H 0 (321 nm), 5 D 4 (362 nm), 5 G 2 (381 nm), 5 L 6 (393 nm), 5 D 3 (414 nm) and 5 D 2 (466 nm). Figure 3b shows the photoluminescence emission spectra of NaYF 4 :Eu 3 + nanophosphor.…”

(Invited) Designing, Synthesis and Optical Properties of Ultrasmall β-NaYF4 Nanocrystals Doped by Lanthanides Ions for Bio-Medical Applications

“…This variety of emission sublines for NaYF 4 :Eu has been related with different sites of Eu ions (surface and volume related). For core-shell sample number of these lines is reduced indicating efficient surface passivation and reducing number of Eu sites [4].…”