Silica‐modified luminescent LaPO₄:Eu@LaPO₄@SiO₂ core/shell nanorods: Synthesis, structural and luminescent properties

Abstract

Monoclinic-type tetragonal LaPO 4 :Eu (core) and LaPO 4 :Eu@LaPO 4 (core/shell) nanorods (NRs) were successfully prepared using a urea-based co-precipitation process under ambientconditions. An amorphous silica layer was coated around the luminescent core/shell NRs via the sol-gel process to improve their solubility and colloidal stability in aqueous and non-aqueous media. The prepared nano-products were systematically characterized by X-ray diffraction pattern, transmission electron microscopy, energy dispersive X-ray analysis, and FTIR, UV/Vis, and photoluminescence spectroscopy to examine their phase purity, crystal phase, surface chemistry, solubility and luminescence characteristics. The length and diameter of the nanoproducts were in the range 80-120 nm and 10-15 nm, respectively. High solubility of the silica-modified core/shell/Si NRs was found for the aqueous medium. The luminescent core NRs exhibited characteristic excitation and emission transitions in the visible region that were greatly affected by surface growth of insulating LaPO 4 and silica layers due to the multiphonon relaxation rate. Our luminescence spectral results clearly show a distinct difference in intensities for core, core/shell, and core/shell/Si NRs. Highly luminescent NRs with good solubility could be useful candidates for a variety of photonic-based biomedical applications.

Mesoporous Silica Modified Luminescent Gd₂O₃:Eu Nanoparticles: Physicochemical and Luminescence Properties

“…The emission band observed at around 585-598 nm is assigned to magnetic dipole transition which is weak with respect to forced electric dipole transition [30,60]. It is fact that forced electric dipole transition ( 5 D0→ 7 F2) is sensitive to the surrounding chemical environment whereas magnetic dipole transition ( 5 D0→ 7 F1) is independent to the surrounding environment [30,47,60,61]. It is obvious from the emission spectra of all three samples the emission efficiency of hypersensitive transition or electric dipole transition is higher than their respective magnetic dipole transition, it suggests that the trivalent europium ions are in the C2 site symmetry.…”

“…Fig.7 illustrate the excitation spectra of core, core/nSiO2 and core/nSiO2/mSiO2 NPs under monitoring 610 ( 5 D0→ 7 F2) nm emission wavelength at room temperature. The excitation spectra consist of several sharp excitation electronic transitions assigned to 7 F0→ 5 H3,6(321), 7 F0→ 5 D4(362), 7 F0→ 5 G3(381), 7 F0→ 5 L6(394), 7 F0→ 5 D3(415), and 7 F0→ 5 D2(466), which are originating from 4f-4f-intra-configurationally transitions of Eu 3+ ions [30,37,47,54,[57][58][59]. Figure 8 demonstrates the emission spectra of core, core/nSiO2 and core/nSiO2/ mSiO2 NPs upon excitation at 395 nm on room temperature.…”

“…( 5 D1→ 7 F1), 578( 5 D1→ 7 F3), 585-599 ( 5 D0→ 7 F1), 605-631 ( 5 D0→ 7 F2), 644-662 ( 5 D0→ 7 F3) and 684-712 ( 5 D0→ 7 F4) transitions, respectively [6,29,30,47,59,60]. Some weak intensity emission transitions located at 470 and 535 nm assigned to 5 D2→ 7 F0 and 5 D1→ 7 F1 transition of Eu 3+ ion, it indicate the low vibrational energy of the Gd-O band [6,58].…”

“…Consequently, the multiphonon relaxation by gadolinium-oxygen vibration is not able to bridge the gaps between the higher energy levels of 5 D2→ 7 F0 & 5 D1→ 7 F1 transition and the 5 D0→ 7 FJ level of Eu(III) ion completely, resulting in the emission from these levels [59]. A prominent emission transition is observed in between 605-630 nm because of 5 D0→ 7 F2 forced electric dipole transition and is hypersensitive to the environment [30,47,60]. The emission band observed at around 585-598 nm is assigned to magnetic dipole transition which is weak with respect to forced electric dipole transition [30,60].…”

“…A prominent emission transition is observed in between 605-630 nm because of 5 D0→ 7 F2 forced electric dipole transition and is hypersensitive to the environment [30,47,60]. The emission band observed at around 585-598 nm is assigned to magnetic dipole transition which is weak with respect to forced electric dipole transition [30,60]. It is fact that forced electric dipole transition ( 5 D0→ 7 F2) is sensitive to the surrounding chemical environment whereas magnetic dipole transition ( 5 D0→ 7 F1) is independent to the surrounding environment [30,47,60,61].…”