Luminescence Studies and Judd–Ofelt Analysis on SiO2@LaPO4:Eu@SiO2 Submicro-spheres with Different Size of Intermediate Shells

Abstract

The novel submicro-spheres SiO2@LaPO4:Eu@SiO2 with core-shell-shell structures were prepared by connecting the SiO2 submicro-spheres and the rare earth ions through an organosilane HOOCC6H4N(CONH(CH2)3Si(OCH2CH3)3 (MABA-Si). The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (IR). It is found that the intermediate shell of the submicro-spheres was composed by LaPO4:Eu nanoparticles with the size of about 4, 5–7, or 15–34 nm. A possible formation mechanism for the SiO2@LaPO4:Eu@SiO2 submicro-spheres has been proposed. The dependence of the photoluminescence intensity on the size of the LaPO4:Eu nanoparticles has been investigated. The intensity ratios of electrical dipole transition 5D0 → 7F2 to magnetic dipole transition 5D0 → 7F1 of Eu3+ ions were increased with decreasing the size of LaPO4:Eu nanoparticles. According to the Judd-Ofelt (J-O) theory, when the size of LaPO4:Eu nanoparticles was about 4, 5–7 and 15–34 nm, the calculated J-O parameter Ω2 (optical transition intensity parameter) was 2.30 × 10−20, 1.80 × 10−20 and 1.20 × 10−20, respectively. The increase of Ω2 indicates that the symmetry of Eu3+ in the LaPO4 lattice was gradually reduced. The photoluminescence intensity of the SiO2@LaPO4:Eu@SiO2 submicro-spheres was unquenched in aqueous solution even after 15 days.

NaGdF4:Eu3+ nanocrystalline: an in-depth study of energy transfer processes and Judd–Ofelt analysis using the luminescence excitation spectrum

“…The variation in the R ratio is insignificant when changing the Eu 3+ concentration. In addition, the R ratio in NaGdF 4 :Eu 3+ nanocrystalline matrices is equivalent to that in some nanocrystalline matrices, such as LaPO 4 :Eu 3+ (1.40), 19 LaAlO 3 :Eu 3+ (1.25), 26 and β-NaGdF 4 :Eu 3+ (1.60), 6 but is lower than that in β-NaGdF 4 :Eu 3+ (2.69), 24 Sr 2 B 2 O 5 :Eu 3+ (2.53), 27 and SrB 2 O 4 :Eu 3+ (3.74). 27 The small value of the R ratio in our case implies that the Eu 3+ ions occur at the high symmetry sites in the NaGdF 4 lattice.…”

“…Thus, the intensity of the 5 D 0 -7 F 2 band is sensitive to the change in the ligand asymmetry, whereas the intensity of the 5 D 0 -7 F 1 MD transition is not affected significantly by the crystal field in the vicinity of the Eu 3+ ions. 17,19 Therefore, the intensity ratio R = I( 5 D 0 -7 F 2 )/I( 5 D 0 -7 F 1 ) is usually used to estimate the asymmetry of the ligand field. For the NaGdF 4 :Eu 3+ nanocrystalline, the R ratio is found to be 1.47, 1.42, 1.49, 1.41, and 1.39 at concentrations of 0.5, 1.0, 2.0, 5.0 and 10.0 at%, respectively.…”

“…where Q is the energy transfer parameter; S represents the interaction mechanism between RE 3+ ions: the S value may be 6, 8, or 10 for the interactions of DD, DQ, or QQ, respectively; and t 0 is the intrinsic lifetime of the donor, which is considered the lifetime of the excited level at a low doping concentration. Because the t 0 value is the lifetime of the Eu 3+ : 5 D 2 level at 0.5 at%, the decay curve at 2.0 at% is fitted to eqn (19). The result is shown in Fig.…”

“…[16][17][18] For these optical properties, the Eu 3+ ion is one of the RE 3+ ions that have been extensively used for spectral applications, such as laser, lighting, and light frequency conversion. [17][18][19][20] Among the MLnF 4 :RE 3+ compounds, the MGdF 4 nanocrystalline exhibits an attractive spectroscopy property, which is the sensitizer role of Gd 3+ ion for the luminescence of RE 3+ under excitation by the characteristic wavelength of Gd 3+ . [21][22][23] Additionally, the energy separation between the 6 G J and 6 P J states in Gd 3+ is equivalent to that between the 7 F 0 and 5 D 0 levels in Eu 3+ ion, so the quantum cutting effect can be observed for MGdF 4 :Eu 3+ matrix under suitable excitation.…”

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

“…Moreover, the modification of the local structure based on strategies such as the control of the doping level, cationic, anionic and cationic/anionic substitution, crystal-site engineering, and the mixing of nanophases are also promising routes [ 14 ]. To date, to improve and optimize the luminescence properties of LaPO 4 -based phosphors, studies have focused on changing the particle size and shape, designing core-shell structures, surface modification, and co-doping with alkali metals [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. However, Ln 3+ activated phosphors suffer from the very low absorption in the near-UV and visible spectral regions due to quantum mechanically forbidden f–f electronic transitions.…”