Photoluminescence study of terbium-exchanged ultrastable Y zeolites: Number of species, photoluminescence decays, and decay-associated spectra

Abstract

Terbium-exchanged ultrastable Y ͑USY͒ zeolites were investigated by using time-resolved photoluminescence spectroscopy techniques and methods. To determine the distribution of terbium species in USY zeolites together with their photoluminescence properties, several analysis methods for the time-resolved luminescence spectra were used such as the area normalization of time-resolved photoluminescence spectra, singular value decomposition, global nonlinear least squares, and the maximum entropy. Except for a questionable long lifetime, small contribution of a terbium species with lifetime of 1.9-2.1 ms, all the experimental and analysis results converged to a two terbium species distribution with lifetimes varying between 410-440 and 1000-1100 s. The effects of the silylation of terbium-exchanged USY zeolites with phenyl-, vinyl-, and hexadecyltrimethoxysilanes on the lanthanide's photoluminescence properties were also described.

Order and disorder effects in nano-ZrO2 investigated by micro-Raman and spectrally and temporarily resolved photoluminescence

“…It is well-known that the ED 5 D 0 -7 F 2 transition is hypersensitive to local symmetry at Eu 3+ sites whereas the MD 5 D 0 -7 F 1 transition is much less sensitive being used as an internal standard in the quantitative estimation of Eu 3+ f-f intensities. [55][56][57][58][59] The intensities ratio corresponding to two transitions (asymmetry ratio, R) has been extensively used as an indicator of the local asymmetry and/or degree of the covalency of the Eu 3+ -oxygen coordination polyhedron. Generally, the lower the R value, the higher the local symmetry at Eu 3+ sites.…”

“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]58 The evolution with the delay time, dt, after the laser/lamp pulse of the asymmetry ratio R can be also used as an indicative for the existence of multiple luminescent species or distribution effects. 35,59 The illustration of the evolution with time of the asymmetry ratio measured at different excitation wavelengths is included in Fig. S7 (ESIw) for ZEB-500 and ZEB-1000.…”

Polymer–microporous host interactions probed by photoluminescence spectroscopy

“…A detailed description of the method is reported in the literature. [31][32][33][34][35] The TRES total area within two spectral ranges 580-600 nm and 605-630 nm corresponding to the 5 D 0 -7 F 1 and 5 D 0 -7 F 2 transitions of europium were analyzed by MaxEnt. The method provides the distribution of the exponential amplitudes versus exponential time constants which best describes the data (as judged by the w 2 ) while being at the same time as simple as possible (as judged by an entropy expression).…”

“…The heterogeneous distribution of the exchanged lanthanides species in faujasites is well documented in the literature and assigned to the dehydration-induced migration of lanthanide's cations. 34,[42][43][44] It is generally assumed that the lanthanides are initially located in the large cages (or supercages) of Y zeolites. Following dehydration, induced by thermal treatment, the ions diffuse through the six-membered rings into the sodalite cages.…”

“…Following dehydration, induced by thermal treatment, the ions diffuse through the six-membered rings into the sodalite cages. 42 Depending on various parameters such as the ionexchange conditions and dehydration protocol, the migration can be partial 34,43 or complete. 44 The exact location of the europium ions in NaY zeolites is beyond the scope of the present study.…”