Lanthanide-Ion-Doping Effect on the Morphology and the Structure of NaYF4:Ln3+ Nanoparticles

Abstract

Two series of β-NaYF4:Ln3+ nanoparticles (Ln = La–Nd, Sm–Lu) containing 20 at. % and 40 at. % of Ln3+ with well-defined morphology and size were synthesized via a facile citric-acid-assisted hydrothermal method using rare-earth chlorides as the precursors. The materials were composed from the particles that have a shape of uniform hexagonal prisms with an approximate size of 80–1100 nm. The mean diameter of NaYF4:Ln3+ crystals non-monotonically depended on the lanthanide atomic number and the minimum size was observed for Gd3+-doped materials. At the same time, the unit cell parameters decreased from La to Lu according to XRD data analysis. The diameter-to-length ratio increased from La to Lu in both studied series. The effect of the doping lanthanide(III) ion nature on particle size and shape was explained in terms of crystal growth dynamics. This study reports the correlation between the nanoparticle morphologies and the type and content of doping lanthanide ions. The obtained results shed light on the understanding of intrinsic factors’ effect on structural features of the nanocrystalline materials.

Effect of Gd3+, La3+, Lu3+ Co-Doping on the Morphology and Luminescent Properties of NaYF4:Sm3+ Phosphors

“…In the NaY 0.98−x Sm 0.02 Ln x F 4 (Ln = La, Gd, Lu) series ( Figure 3 b, Figure 4 , Figure 5 and Figure 6 ), the substitution of the yttrium ion by the lanthanum and lutetium ions results in particle size increase, whereas particle size reduction is observed upon gadolinium doping, Figure 7 . This observation can be explained by the mechanism of crystal growth [ 10 ]. We assume that the particle size is determined by nucleation and crystal growth rates.…”

“…In the NaY 1−x Sm x F 4 series, the substitution of Y 3+ by Sm 3+ ions leads to the particle size reduction from 682 nm (NaYF 4 ) down to 78 nm (NaY 0.5 Sm 0.5 F 4 ). Co-doping of NaY 0.98 Sm 0.02 F 4 by La 3+ and Lu 3+ ions results in particle size increases due to faster growth (for La 3+ ) and slower nucleation (for Lu 3+ ) [ 10 ]. In contrast to La 3+ and Lu 3+ , co-doping of these materials by Gd 3+ ions leads to particle size reduction because the lowest growth/nucleation rates are characteristic of Gd 3+ .…”

“…The optical properties of these materials depend on the particles’ size and morphology, crystal symmetry, type, and concentration of rare earth ions in the host matrix [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Sodium yttrium fluoride is one of the best host matrices for luminescent rare earth-doped inorganic materials because this matrix has only low-frequency vibrational modes, and therefore does not quench the luminescence.…”

“…This approach neglects the fundamentally interesting details of the mutual effect of ions on similar electronic structures. Previously we have reported the particle size and shape dependence on the nature of the doping lanthanide (III) ions NaYF 4 :Ln 3+ series and described the correlation between the obtained nanoparticle morphologies and the type and content of doping ions [ 10 ]. We found that the average diameter of particles reaches the least value for Sm 3+ , Eu 3+ , and Gd 3+ doped materials.…”

Novel Sol-Gel Route to Prepare Eu3+-Doped 80SiO2-20NaGdF4 Oxyfluoride Glass-Ceramic for Photonic Device Applications

“…He, F. et al [46] described the preparation of hexagonal NaGdF 4 nanoparticles via hydrothermal synthesis where the crystal size increased from 170 nm to 1 µm when the reaction time increased from 2 h to 24 h. The growth of NaGdF 4 nanoparticles during hydrothermal synthesis is associated with a nucleation process followed by a crystal growth. Thus, the nucleation rate determines the growing crystal rate, and both processes are in competition [47]. Figure 2 shows the HR-TEM images corresponding to 1.5Eu 3+ : NaGdF4-20 nanoparticles heat-treated at 450 °C for 5 h. Figure 2a shows nanoparticles with irregular shapes and sizes around 30 nm, around double of that calculated with the W-H plot, which is associated with the tendency of nanoparticles to agglomerate during synthesis and further centrifugation to obtain powders.…”