ABSTRACT
Assembly system with MCM-41 doped with Yb3+ as a host, and Tb(aspirin) 3phen, which had been heat treated, as an active optical guest, was synthesized at room temperature. The structure and physical properties of the composites were characterized by a combination of different techniques such as XRD, N2 adsorption-desorption and IR, while the photoluminescence properties of the composites were analyzed by PL. Excitation and emission spectra were examined to explore the PL properties of the prepared samples and the relationship between the optical guest and the inorganic host. The present paper reports a new synthesis method called "Direct-Calcination" to avoid the loss of rare earth ions in the process of synthesis. Strong reflections at 2theta = 2.6 attributed to (100) reflection were presented in XRD patterns of both Yb/MCM-41 and Tb(aspirin) 3phen-Yb/MCM-41, which always can be observed for regular, spherical structure of MCM-41 materials, and the inorganic framework order increased after Tb(aspirin) 3phen being incorporated into the channels of Yb/MCM-41. The intensity of the band at 963 cm(-1) decreased in IR spectrum of Yb/MCM-41, relative to that in IR spectrum of MCM-41, implying that Yb3+ had been banded with the framwork. And a sharp band at 1 384 cm(-1) in IR spectrum of Tb(aspirin) 3phen-Yb/MCM-41 also gives the characteristic information about the bands in Tb(aspirin) 3phen-MCM-41. The results from the characterization of PL show that the wide excitation band over 240-375 nm of Tb(aspirin) 3phen is assigned to the carbonyl group n --> pi* transition absorption, benzene ring pi --> pi* transition absorption of aspirin, and phenanthrene absorption of phen. The luminescence intensity of Tb(aspirin) 3phen incorporated into the channels of MCM-41 can be enhanced by heat treating in the synthesis process of Tb(aspirin) 3phen, while the intensity also can further increases by doping Yb3+ in the silicon framework of MCM-41. The luminescence intensity of the assembly system gets to maximum when Yb/Si ratio is 7.579 x 10(-3).
ABSTRACT
Highly ordered mesoporous material MCM-41A(after calcination) and MCM-41B (before calcination) were synthesized in ethylenediamine (EDA) medium at room temperature, and the rare earth complexes Tb(aspirin)3phen which had been heat treated as an active optical guest was incorporated into the one-dimensional channels of MCM-41A(B). The photoluminescence properties of the organic/inorganic composites Tb(aspirin)3phen-MCM-41A(B) were investigated based on the analyses of excitation and emission spectra to provide information about the relationship between the organic host and the inorganic optical guest. The results from the characterization of PL show that the wide excitation band in the range of 240-375 nm of Tb(aspirin)3 phen is assigned to the carbonyl group n --> pi* transition absorption, benzene ring pi --> pi* transition absorption of aspirin, and phenanthrene absorption of phen. As no excitation band appears in ultraviolet ranges, the characteristic emission peaks of Tb3+ in the emission spectra are related to antenna effect Relative to the excitation band of Tb(aspirin)3phen, the excitation band of Tb(aspirin)3phen-MCM-41B and Tb(aspirin)3phen/MCM-41A splits obviously, and only one narrow excitation peak at 353 nm appears in the excitation spectrum of Tb(aspirin)3 phen-MCM-41A. The excitation bands of Tb(aspirin)3 phen-MCM-41B and Tb (aspirin)3 phen/MCM-41A at short wavelength weakens and disappears gradually, while excitation peaks at long wavelengths is enhanced gradually, and the IL/ILn ratio I, where IL is the emission intensity at 405 nm under 335 nm excitation, and I(Ln) is the emission intensity at 544 nm under 335 nm excitation, also decreases correspondingly. It is suggested that the triplet states and single states of aspirin and phen reduce with different degree after Tb(aspirin)3phen is banded with MCM-41 framework, and the effect of silicon framework on the states of phen is more than that of aspirin. The degree of the effect on the states of organic ligands is in the order of: MCM-41B external surface > MCM-41A external surface > MCM-41A inside surface. In addition, the ratio I also could indicates the degree of the effect of MCM-41 surface lattice field on the ligand energy level and the content of Tb (aspirin)3phen on the MCM-41 surface.
