Sol–gel synthesis and characterization of SiO₂@CaWO₄,SiO₂@CaWO₄:Eu³⁺/Tb³⁺core–shell structured spherical particles

Abstract

Nanocrystalline CaWO 4 and Eu 3+ (Tb 3+)-doped CaWO 4 phosphor layers were coated on non-aggregated, monodisperse and spherical SiO 2 particles by the Pechini sol-gel method, resulting in the formation of SiO 2 @CaWO 4 , SiO 2 @CaWO 4 :Eu 3+ /Tb 3+ core-shell structured particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core-shell structured materials. Both XRD and FT-IR indicate that CaWO 4 layers have been successfully coated on the SiO 2 particles, which can be further verified by the FESEM and TEM images. The PL and CL demonstrate that the SiO 2 @CaWO 4 sample exhibits blue emission band with a maximum at 420 nm (lifetime = 12.8 µs) originated from the WO 2− 4 groups, while SiO 2 @CaWO 4 :Eu 3+ and SiO 2 @CaWO 4 :Tb 3+ show additional red emission dominated by 614 nm (Eu 3+ : 5 D 0-7 F 2 transition, lifetime = 1.04 ms) and green emission at 544 nm (Tb 3+ : 5 D 4-7 F 5 transition, lifetime = 1.38 ms), respectively. The PL excitation, emission and time-resolved spectra suggest that there exists an energy transfer from WO 2− 4 to Eu 3+ and Tb 3+ in SiO 2 @CaWO 4 :Eu 3+ and SiO 2 @CaWO 4 :Tb 3+ , respectively. The energy transfer from WO 2− 4 to Tb 3+ in SiO 2 @CaWO 4 :Tb 3+ is more efficient than that from WO 2− 4 to Eu 3+ in SiO 2 @CaWO 4 :Eu 3+ .

Monodisperse and core–shell structured NaYF4:Ln@SiO2 (Ln=Yb/Er, Yb/Tm) microspheres: Synthesis and characterization

“…For pure SiO 2 in Fig. 5a, the absorption bands due to OH (3445 cm −1 ), H 2 O (1629 cm −1 ), Si-O-Si ( s , 1083 cm −1 ; as , 802 cm −1 ), Si-OH ( s , 964 cm −1 ), and Si-O (ı, 464 cm −1 ) (where s represents symmetric stretching, as asymmetric stretching, and ı bending) are clear [24][25][26][27][28][29][30]. The strong bands of OH (3445 cm −1 ) and H 2 O (1629 cm −1 ) reveal that a large number of OH groups present, which are important for bonding metal ions from the impregnating colloid.…”

“…Furthermore, this kind of core-shell phosphors are superior to conventional pure rare-earth-based phosphors in actual applications because silica is much cheaper than most of the phosphors, which often use the expensive rare-earth elements as the activators and/or host components. Therefore, a series of core-shell structured materials by coating down-conversion phosphors on spherical silica have been prepared [24][25][26][27][28][29][30].…”

Luminescent silicate core–shell nanoparticles: Synthesis, functionalization, optical, and structural properties

“…For the fabrication of many inorganic phosphor materials, these temperatures are too low. Traditionally, macroscopic phosphor materials are produced by solid-state reaction at temperatures of about 200-1500°C or under pressure in an autoclave [1,[13][14][15][16][17][18]. The disadvantage of such reactions is the difficulty to control the particle size and size distribution and to obtain a homogeneous product [19].…”

Sol–gel preparation and characterization of uniform core-shell structured LaInO3:Sm3+/Tb3+@SiO2 phosphors

“…However, in most cases, the uniformity of the coating layer (shell) is low and it is difficult to control the shape and size of the final products. Among all the synthesis methods, a modified Pechini sol-gel process has been proved an efficient methodology to coat uniform crystalline thin film on the surface of silica spheres, using inorganic salt as precursor, citric acid as chelating agents, and poly (ethylene glycol) (PEG) as cross-linking ligands [37][38][39][40][41][42].…”