A family of mesoporous silica microspheres with fibrous morphology and different particle sizes ranging from about 400 to 900 nm has been successfully synthesized through a facile self-assembly process. The structural, morphological, and textural properties of the samples were well characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), N(2) adsorption/desorption, and thermal gravimetry (TG). The results reveal that this silica-based mesoporous material exhibits excellent physical properties, including a fibrous spherical morphology, good thermal stability, large pore volume, high specific surface area and narrow size distribution. Additionally, the size and textural properties can be tuned by altering the silica precursor/template molar ratio. The formation and the self-assembly evolution process have also been proposed. The obtained materials were further used as a drug delivery carrier to investigate the in vitro drug release properties using doxorubicin (DOX) as a representative model drug. It was found that this kind of silica exhibits good biocompatibility and obvious sustained drug release properties, suggesting its potential application in biological fields.
Yttrium tungstate precursors with novel 3D hierarchical architectures assembled from nanosheet building blocks were successfully synthesized by a hydrothermal method with the assistance of sodium dodecyl benzenesulfonate (SDBS). After calcination, the precursors were easily converted to Y(2)(WO(4))(3) without an obvious change in morphology. The as-prepared precursors and Y(2)(WO(4))(3) were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra, respectively. The results reveal that the morphology and dimensions of the as-prepared precursors can be effectively tuned by altering the amounts of organic SDBS and the reaction time, and the possible formation mechanism was also proposed. Upon ultraviolet (UV) excitation, the emission of Y(2)(WO(4))(3):x mol% Eu(3+) microcrystals can be tuned from white to red, and the doping concentration of Eu(3+) has been optimized. Furthermore, the up-conversion (UC) luminescence properties as well as the emission mechanisms of Y(2)(WO(4))(3):Yb(3+)/Ln(3+) (Ln = Er, Tm, Ho) microcrystals were systematically investigated, which show green (Er(3+), (4)S(3/2), (2)H(11/2)→(4)I(15/2)), blue (Tm(3+), (1)G(4)→(3)H(6)) and yellow (Ho(3+), (5)S(2)→(5)I(8)) luminescence under 980 nm NIR excitation. Moreover, the doping concentration of the Yb(3+) has been optimized under a fixed concentration of Er(3+) for the UC emission of Y(2)(WO(4))(3):Yb(3+)/Er(3+).
In the present paper, we first demonstrate a facile and rapid precipitation process to fabricate Y(OH) 3 with tailored well-defined shapes and excellent uniformity in the presence of sodium citrate. The morphologies and sizes of the products can be controlled by simply tuning the sodium citrate amounts, the reaction temperature, and the amount of NaOH. After calcination, the Y(OH) 3 precursors were easily converted to pure Y 2 O 3 with no obvious change in morphology. The phases, morphologies, sizes as well as up-conversion (UC) photoluminescence of as-prepared products were well characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra, respectively. The UC emission properties of the prepared Y 2 O 3 :Yb 3+ /Ln 3+ (Ln ¼ Er, Tm and Ho) were investigated in detail. Under 980 nm NIR excitation, the emission intensity and the corresponding luminescent colors of Y 2 O 3 :Yb 3+ /Ln 3+ (Ln ¼ Er, Tm and Ho) could be precisely modulated by changing the doping concentration of Yb 3+ ions. Furthermore, the experimental results also reveal that the optical properties of the Y 2 O 3 :1%Yb 3+ /1%Ho 3+ phosphors with different morphologies are strongly dependent on their morphologies and sizes.
Highly uniform α-NaYF4:Yb/Er hollow microspheres have been successfully prepared via a simple two-step route. First, the core-shell structured MF@Y(OH)CO3:Yb/Er precursor was fabricated by a urea-based homogeneous precipitation method using colloidal melamine formaldehyde (MF) microspheres as template. Then the Y(OH)CO3:Yb/Er precursor was transformed into hollow NaYF4:Yb/Er (α and β mixed phase) by a subsequent solvothermal method, and MF microspheres were dissolved in the solvent simultaneously. The mixed phase of NaYF4:Yb/Er was transferred into pure α-NaYF4:Yb/Er by calcination. The as-prepared hollow microspheres were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrum (EDS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and upconversion (UC) luminescence spectroscopy. It is found that the template can be removed without additional calcination or etching process. α-NaYF4:Yb/Er hollow microspheres exhibit bright upconversion (UC) luminescence under 980 nm laser diode (LD) excitation. Furthermore, the hollow microspheres show sustained and pH-dependent doxorubicin hydrochloride (DOX) release properties; in particular, the emission intensity increases with the release amount of drug, making the release process able to be tracked or monitored by the change of the emission intensity, which demonstrates the high potential of this kind of hollow fluorescent material in drug delivery fields.
In the present paper, NaLa(WO 4 ) 2 microcrystals with diverse morphologies, sizes and dimensions have been synthesized via a mild and controllable hydrothermal process using polyvinylpyrrolidone (PVP) as surfactant. The phases, morphologies, sizes, and photoluminescent properties of the as-prepared products were well characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra, respectively. The results indicate that the phase, morphology, and size of the NaLa(WO 4 ) 2 microcrystals can be tuned in a controlled manner by altering the amount of PVP, pH value of the initial solution, and the reaction time. The crystal growth was thoroughly investigated, and a possible formation mechanism was proposed. It is expected that the synthetic strategy can be extended to controllable synthesis of other types of microcrystals as well. Upon ultraviolet (UV) excitation, the NaLa(WO 4 ) 2 :Ln 3+ (Ln ¼ Eu, Tb) microcrystals exhibit bright red (Eu 3+ , 5 D 0 / 7 F 2 ) and green (Tb 3+ , 5 D 4 / 7 F 5 ) luminescence. The dependence of NaLa(WO 4 ) 2 :Tb 3+ luminescence intensity on different morphologies has been investigated in detail. Furthermore, the upconversion (UC) luminescent properties as well as the emission mechanisms of NaLa(WO 4 ) 2 :Yb 3+ /Ln 3+ (Ln ¼ Er, Tm, Ho) microcrystals were systematically investigated, which show respective green (Er 3+ , 4 S 3/2 , 2 H 11/2 / 4 I 15/2 ), blue (Tm 3+ , 1 G 4 / 3 H 6 ) and yellow (Ho 3+ , 5 S 2 / 5 I 8 ) luminescence under 980 nm NIR excitation.
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