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Terbium-exchanged MFI zeolite type materials, i.e., microporous-mesoporous Zeotile-1 with the Si/Al ratio in the range 33-200, Zeogrid with the Si/Al ratio of 75, and nanocrystalline MFI with the Si/Al ratio of 75, were prepared via an ion exchange procedure. All of these zeolites were investigated by means of time-resolved photoluminescence techniques in various hydration states: as-synthesized (hydrated), calcined (heated at 450 degrees C in air), and rehydrated (after a six-month exposure to the atmospheric moisture). The photoluminescence decays and spectra were analyzed by discrete exponential fitting, distribution lifetimes analysis, and area-normalized time-resolved photoluminescence spectra. The results sustained a single average terbium species coordinated to both water molecules and framework oxygens in the hydrated zeolites. The framework contribution increased with the Si/Al ratio in Zeotile-1 and was greatest for the nanocrystalline MFI zeolite. For the calcined Zeotile-1 and Zeogrid, two main terbium species of different environments were found. For the nanocrystalline Tb3+-MFI, a distinct number of species could not be inferred, indicating a more heterogeneous distribution. Rehydration further differentiated among the Tb3+-exchanged zeolites. Photoluminescence line shape and decay of Tb3+-Zeotile-1 were between those of the hydrated and calcined states indicating a slow rehydration rate in contrast with the photoluminescence properties of Tb3+-MFI, which fully recovered the values of the hydrated state. Tb3+-Zeogrid presented an intermediate case: while the PL line shape was fully restored to that measured for the hydrated sample, the decay was still longer than that measured with the hydrated sample. Terbium photoluminescence response related to zeolite texture, Si/Al ratio, and hydration state suggest different sitting and location of terbium in Zeotile-1, Zeogrid, and nanocrystalline MFI materials. In mesoporous Zeotile-1 and Zeogrid, the results sustained two types of terbium sites: one on the internal surface of mesopores, the other inside the pores, while for the nanocrystalline MFI, terbium sites inside the pores predominate.

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Terbium-exchanged BEA zeolites were hydrophobized with phenyl-, vinyl-, and hexadecyltrimethoxysilanes by means of postsynthesis grafting. These materials were investigated using XRD, FT-IR, TGA, physical adsorption, and photoluminescence. Different methods for the analysis of the non-exponential decay of terbium photoluminescence in BEA zeolites were used ranging from discrete exponential to more complex approaches based on maximum entropy and global analysis. Two groups of decay times varying between 480 and 580 micros and 1-1.3 ms were assigned to the lifetimes of terbium exposed to water (unprotected) and protected by the organic groups, respectively. Our results showed that the preservation of terbium PL properties against detrimental effects of moisture adsorption could be ordered in the following sequence: hexadecyl > phenyl approximately vinyl. The photoluminescence results were in good agreement with the FT-IR, TGA, and physical adsorption data.

The optical response of europium ions in the parent (non-silylated) and silylated microporous-mesoporous Zeogrid materials was investigated in detail in relation to Zeogrid structure. All materials were characterized using nitrogen adsorption isotherms, powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry, and time-resolved photoluminescence spectroscopy. A two europium species distribution with distinct luminescence spectra and lifetimes was found for both parent and silylated Zeogrid. In the parent Zeogrid, the short-lived europium species is characterized by the intensity ratio R=I(5D0-(7)F2)/I(5D0-(7)F1) or asymmetry values of approximately 0.4-0.7 and photoluminescence (PL) lifetimes of 110-125 micros and therefore is assigned to an almost fully hydrated europium species. In the silylated Zeogrid, the short-lived europium species is characterized by asymmetry values of 1.0-2.4 and lifetimes of 160-180 micros suggesting a relatively distorted europium environment. The long-lived europium species exhibits similar asymmetry ratios in the parent and silylated Zeogrid, which vary between 5.0 and 6.2 with increasing Si to Al ratio from 25 to 150 and slightly different PL lifetimes. The mechanism responsible for the intensity of the electric and magnetic forbidden 5D0-(7)F0 transition was determined to be J-mixing of the 7F2 into the 7F0 state through the axial second-order crystal-field potential. The comparison between the photoluminescence properties of europium in the parent and silylated Zeogrid demonstrates that the effects of rehydration were strongly suppressed following silylation.