Particle size effects on the structure and emission of Eu3+:LaPO4 and EuPO4 phosphors

Abstract

This paper provides the detailed study of (nano)particle's size effect on structural and luminescent properties of LaPO 4 :Eu 3+ synthesized by four different methods: high temperature solid-state, co-precipitation, reverse micelle and colloidal. These methods delivered monoclinic monazite-phase submicron particles (> 100 nm), 4 × 20 nm nanorods and 5 nm spheres (depending on the annealing temperature), 2 × 15 nm nanorods, and ultrasmall spheres (2 nm), respectively. The analysis of emission intensity dependence on Eu 3+ concentration showed that quenching concentration increases with a decrease of the particle size. The critical distance for energy transfer between Eu 3+ ions is found to be 18.2 Å, and the dipole-dipole interaction is the dominant mechanism responsible for the concentration quenching of emission. With the increase in Eu 3+ concentration, the unit-cell parameter slightly increases to accommodate larger Eu 3+ ions at sites of smaller La 3+ ions. Photoluminescent emission spectra presented four characteristic bands in the red spectral region: at 592 nm (5 D 0 → 7 F 1), at 612 nm (5 D 0 → 7 F 2), at 652 nm (5 D 0 → 7 F 3) and at 684 nm (5 D 0 → 7 F 4), while in small colloidal nanoparticles additional emission bands from host defects appear at shorter wavelengths. Intensities of f-f electronic transitions change with particles size due to small changes in symmetry around europium sites, while emission bandwidths increase with the reduction of particle size due to increased structural disorder. Judd-Ofelt analysis showed that internal quantum yield of Eu 3+ emission is strongly influenced by particle's morphology.

Surface Plasmon Enhancement of Eu3+ Emission Intensity in LaPO4/Ag Nanoparticles

“…The mole percentages (mol %) of Ag NPs in the samples were calculated relative to the overall content in the Ag/La 0.95 Eu 0.05 PO 4 nanostructures. According to our previous results [13], there is no concentration quenching in RE 3+ -doped LaPO 4 NPs and the emission intensity increases with an increase in RE 3+ dopant concentration up to the full substitution of La 3+ with RE 3+ . We chose the La 0.95 Eu 0.05 PO 4 system where the Eu 3+ emission is strong enough so that the effect of Ag NPs on the luminescence efficiency can be clearly observed.…”

“…The absence of impurity phases indicates that the dopant Eu 3+ ions are successfully incorporated into the LaPO 4 matrix due to the equal valence (+3) and similar ionic radii between the Eu 3+ (a = 0.112 nm) and La 3+ ions (a = 0.122 nm) [35]. In this crystal structure, the lanthanide ions are coordinated with nine oxygen atoms forming polyhedrons (LaO 9 ) that a share corner with PO 4 tetrahedra in which all four P-O bonds are equivalent (Figure 2b,c) [13,36]. The average crystallite size of~6 nm was determined using built-in software and was similar for all the samples.…”

“…In recent years, the lanthanum orthophosphate (LaPO 4 ), non-toxic, biocompatible, thermally, chemically, and photo-stable material has been recognized Materials 2020, 13, 3071 2 of 10 as an excellent choice for rare-earth ion doping [8][9][10][11][12]. Due to the similar ionic radii and charge, lanthanum ion (La 3+ ) can be easily replaced with different rare-earth (RE 3+ ) ions (e.g., Eu 3+ , Dy 3+ , Sm 3+ ) at a wide range of concentrations without significantly affecting the lattice structure [13].…”

High resolution luminescence spectroscopy and thermoluminescence of different size LaPO4:Eu3+ nanoparticles

“…The LaPO 4 :10mol%Eu 3+ nanoparticles of different sizes and morphologies were synthesized by reverse micelle and co-precipitation technique by analogy to the methods presented in our previous paper [19].…”

Novel tantalum phosphate Na13Sr2Ta2(PO4)9: synthesis, crystal structure, DFT calculations and Dy3+-activated fluorescence performance

“…As an important family of phosphors, rare-earth phosphate-based phosphors have been developed due to their excellent properties, such as low cost, good chemical stability, low synthesizing temperature and environmental benignity. This research effort originated from a large number of research papers on new efficient phosphors, including K 2 Ba 3 (P 2 O 7 ) 2 :Ce 3+ /Tb 3+ (Meng et al, 2017), ALnP 2 O 7 :Eu 3+ (A = Rb, Cs, TI; Ln = Y, Lu, Tm; Mbarek, 2017), K 8 Nb 7 P 7 O 39 :Eu 3+ (Zhao et al, 2016), Na 3 La(PO 4 ) 2 :Eu 3+ /Tb 3+ /Dy 3+ (Zhao et al, 2017), K 3 Gd(PO 4 ) 2 : Sm 3+ (Gupta et al, 2015), KBaBP 2 O 8 :Dy 3+ (Han et al, 2015), Ba 3 P 4 O 13 :Eu 2+ (Wu et al, 2018), Ca 6 Ba(PO 4 ) 4 O:Eu 2+ (Ji et al, 2016), Ca 3 (PO 4 ) 2 :Eu 2+ (Ji et al, 2015), LaPO 4 :Eu 3+ (Gavrilovic et al, 2018), CdBaP 2 O 7 :Eu 2+ (Derbel et al, 2016), KBa 2 (PO 3 ) 5 :Sm 3+ (Zhao et al, 2018), Ca 6 BaP 4 O 17 :Ce 3+ (Komuro et al, 2015), RbZnPO 4 :Eu 3+ (Xin et al, 2015), Na(Ba/Sr/Ca)PO 4 :Eu 2+ (Bai et al, 2017) and Ca 9 Ce(PO 4 ) 7 : Mn 2+ ,Tb 3+ (Zhang, Li et al, 2017). The fundamental building unit of phosphate compounds is the PO 4 tetrahedron, which is flexible and can inhibit various coordination environments by altering the P-O bond lengths.…”