The strong red emission peak further suggested that Eu3+ existed in the surface of the SiO2 hollow sphere. The emission spectrum of SiO2 · Eu2O3 HSs consisted of peaks mainly located in the wavelength range from 570 to 700 nm. These peaks corresponded to transitions from the excited state 5 D 0 to the ground state 7 F J (J = 0, 1, 2, 3, 4) of the 4f 6 configuration of Eu3+, as marked in Figure 3. Luminescence originating from

transitions between 4f levels is predominant due to electric dipole or magnetic dipole interactions [40–44]. As can be seen in Figure 3, the strong red emission peak at 612 nm originating from the electric dipole transition 5 D 0 to 7 F 2 was the dominant Crenigacestat chemical structure band in the measured spectrum. The emission peak at around 590 nm was attributed to the 5 D 0 to 7 F 1 transition. The peaks located at 648 and 695 nm corresponded to 5 D 0 to 7 F 3 and 5 D 0 to

7 F 4 transitions, respectively. Figure 3 The emission spectrum of SiO 2 ∙Eu 2 O 3 HSs. The insert is digital image of SiO2∙Eu2O3 HSs under UV light. Figure 4 shows the Brunauer-Emmett-Teller (BET) N2 adsorption-desorption isotherms and the pore size distribution of the as-prepared SiO2 · Eu2O3 HSs. The BET specific surface area and the total pore Mocetinostat concentration volume of the SiO2 · Eu2O3 HSs were measured to be 308.6 m2/g and 0.307 cm3/g, respectively. The pore diameter distribution was relatively wide according to the data of the adsorption branch of the isotherm. The

as-prepared SiO2 · Eu2O3 HSs with a mesoporous Selleckchem YH25448 structure may possess good performance in drug delivery efficiency, catalytic activity, and so on. Figure 4 N 2 adsorption-desorption isotherm and pore size distribution (insert) of SiO 2 ∙Eu 2 O 3 HSs. Influencing factors of the synthetic process of SiO2 · Re2O3 (Re = Y, Eu, La, Sm, Tb, Pr) hollow structures The experiments showed that the pH value of the solution, reaction temperature and time, and different rare-earth ions and concentrations played an outstanding role in the synthesis of SiO2 · Re2O3 hollow structures, which are discussed in detail as follows. Effect of the pH value of the solution The pH value of the solution was adjusted with dilute nitric acid. The Rolziracetam studied pH range was from 7 to 3 under the following reaction conditions: Re3+ = 0.06 mol/L and T = 250°C. Hollow-structure particles could be obtained under the range of 4 ≤ pH < 5.5, and the optimum pH value was 4.5. No hollow structure products appeared when 6 ≤ pH ≤ 8. No HSSs appeared when 2 < pH < 3. Normally, a few HSSs could have emerged in the product at the conditions of 3 < pH < 4.0 or 5 < pH < 6 if the reaction time was more than 10 h. The detailed results are shown in Additional file 1: Table S1 and Figure S3. It is known that SiO2 is an amphoteric oxide which can dissolve into an acidic or basic solvent. The experiments showed that a weak acid solution was in favor of hollow structure formation.

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