Luminescence of nanoporous C12A7 compound

Abstract

A comparison of excitation spectra of photostimulated and ordinary luminescence enabled us for the first time to determine experimentally the framework energy gap value E g = 6.5 eV of 12CaO · 7 Al 2 O 3 (C12A7). The most short-wavelength luminescence band (peaked at ~4.5 eV) detected at 10 K can be interpreted either as luminescence of intrinsic excitations or as recombination of electrons, captured in subnanometer sized cages of C12A7 crystal structure, with holes of valence band. The main peak of thermostimulated luminescence (134-137 K) is composed of two emission bands peaked at 2.8 and 4.5 eV. The calculated activation energy 0.44 eV of spectrally resolved (at 4.5 eV) thermally stimulated luminescence peak at 137 K is close to the value (0.4 eV) needed to initiate the inter-cage charge transfer of electrons (polaron hopping) between cages.

VUV and cathodoluminescence spectroscopy of 12CaO · 7Al2O3

“…[8], their energy states, strongly influence the top of the valence band (VB) of C12A7 and consequently modulate the electronic structure. Samples of C12A7 thermally treated in the atmosphere of various oxygen content were investigated in our previous work [9], where we got preliminary estimate for E g * 6.5 eV by means of the photostimulated luminescence method. In present work, we used samples where the encaged oxygen was partly replaced by electrons using the melt-solidification process in reducing atmosphere [12].…”

“…Our first results on luminescence properties of C12A7 were published recently in [9]. The aim of the present study is to elucidate the electronic structure of this unique compound benefiting from the recent progress in synthesis and post-synthesis treatment of C12A7 ceramics and single crystals.…”

Characteristics, Thermodynamics, and Preparation of Nanocaged 12CaO·7Al2O3 and Its Derivatives

“…In addition to its special structure and outstanding performances, C12A7 is considered as a functional oxide with broad band gap (~5.9 eV) compared with other compounds constituted of CaO and Al 2 O 3 . Feldbach et al . experimentally determined energy gap of C12A7 framework to be 6.5–6.8 eV.…”

“…experimentally determined energy gap of C12A7 framework to be 6.5–6.8 eV. They discovered that nanoporous C12A7 compound showing luminescence properties at low temperature with the most intensive short‐wave length luminescence band of ~4.5 eV appeared at 10 K in 2007 …”

“…Hosono and his team in Tokyo University have studied C12A7 since 1980s. They first found superoxide radical ion in C12A7 in 1987 .…”