Study On The Fabrication And The Influential Factors Of Photoluminescence For EuPO₄:Zn@MCM-41 Composites

Due to the ordered arrangement, large surface area and chemical stability of mesoporous silica materials MCM-41, the pore size and volume of MCM-41 materials, which make them suitable for hosts to various guest extensively. The composites of photoluminescence (PL), which were obtained by encapsulating the luminescent guest, have many advantages such as high emission intensity, uniform particle size and less expensive.A series of MCM-41 with the pore sizes ranged from 2.73 to 6.56 nm were synthesized by hydrothermal method under microwave irradiation, and the EuPO₄:Zn@MCM-41 composites were obtained through a simple Pechini sol–gel process. The EuPO₄:Zn crystals were deposited onto MCM-41 surface and the amorphous phase of EuPO₄:Zn was also encapsulated into its pores. The influential factors which including the adding amount of Eu(NO₃)₃·6H₂Oand Zn(NO₃)₂·6H₂O, the calcination temperature and calcination time, and the pore sizes of MCM-41 were investigated by the PL intensity emitted at 593nm. Besides, all of the influential mechanisms were investigated. The physicochemical properties of the samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption/desorption, energy-dispersive spectrometry (EDS), and selected area electron diffraction (SAED).The PL spectra indicated that the Pure EuPO₄: Zn powders didn't show any PL emission, but the EuPO₄:Zn @ MCM-41 composites had strong blue (468nm) and orange (593nm) PL emission. The main bands at 593 nm ascribe to the 5D0–7F1 transitions of Eu³⁺ and are the magnetic-dipole (M1) allowed transition, decided by the symmetry of the Eu³⁺ centers. The PL results showed that the agglomeration of EuPO₄:Zn particles decreased and the particles became small, due to the dispersing effect of MCM-41. Besides, larger splitting of Eu³⁺ centers and less overlapping of Eu³⁺ electron atmosphere were achieved by the MCM-41, suggesting that MCM-41 was an effective host for Eu³⁺ complex for lowering the luminescence quenching effect.The PL intensity of EuPO₄:Zn@MCM-41 was affected seriously by the preparation conditions and the pore size of MCM-41. There was strong PL emission for the composites when the attending mount of Eu(NO₃)₃·6H₂O,Zn(NO₃)₂·6H₂O were 0.001mol and 0.002mol. Under this condition, the ration for Eu³⁺(the PL centers in the composites) and Zn²⁺( the taps in the lattice) was 9.44%:0.37%, which can coordinated with the residual PO43- (9.80%) at ration of 1:1properly. When the composites heated under 800℃for 5h,the good crystal structure were obtained. The PL intensity of EuPO4:Zn@MCM-41 depended on the mesoporous silicate material's pore size. The PL intensity was increased along with MCM-41 pore size until d≤3.1125 nm, but decreased generally when d continued increasing. There are three factors responsible for the PL intensity of Eu³⁺, including the density of QDs (Quantum Dots), the splitting of the centers of Eu³⁺ and the degree of agglomeration of QDs. All of the above factors have a relation to pore size of MCM-41 finally, which changed selection rules and effected magnetic-dipole allowed transition probabilities of particular f–f transitions. Besides, the dispersion effect of MCM-41 was also proved. Using of a suitable pore size, the PL material with much stronger emission can be synthesized which will have potential applications on optoelectronic devices.