High Density Hydroxyl Anions in a Microporous Crystal: [Ca 24 Al 28 O 64 ] 4+ ·4(OH - )

By retreating the C12A7-O - microporous crystal ([Ca 24 Al 28 O 64 ] 4+ ·4O - ) in a high-temperature (1350 °C) and water vapor environment, almost 100% O - and O 2 - anions in C12A7-O - have been substituted by the OH - anions, leading to the formation of a high-intensity OH - emission material, [Ca 24 Al 28 O 64 ] 4+ ·4OH - (C12A7-OH - ). The formation of OH - in C12A7-OH - was identified by investigating the anionic species both on the surface and in the bulk as well as its emission features with Fourier-transform IR absorption, electron paramagnetic resonance, and time-of-flight mass spectra. The concentration of OH - anions in C12A7-OH - is estimated to be more than 7 × 10 20 cm -3 . Furthermore, a sustainable and stable OH - emission current of 11.7 μA/cm 2 from C12A7-OH - has been obtained at a sample surface temperature of 780 °C under an extraction field of 1300 V/cm. The emission features of C12A7-OH -, such as temperature and field effects, have been also investigated. It is expected that the present material could be practically used as an OH - anions storage and generator.