Photoluminescence characteristics of ZnO clusters confined in the micropores of zeolite L

Sub-nanometric ZnO clusters were prepared in the micropores of zeolite L by the incipient wetness impregnation method. The X-ray patterns (XRD), transmission electron microscope (TEM), N₂ adsorption-desorption isotherms, UV-vis absorption spectra (UV-vis) and photoluminescence spectra (PL) were used to characterize the composite materials. The results indicate that a small amount of sub-nanometric ZnO clusters can be introduced into the channel of zeolite L, however, when the amount of ZnO loading exceeds 20 wt%, macrocrystalline ZnO appears on the external surface of zeolite L. Different from bulk ZnO materials, these sub-nanometric ZnO clusters exhibit their absorption onset below 255 nm and a blue luminescence band in the range of 404-422 nm. The temperature-dependent luminescence demonstrates that the amount of the ZnO loading significantly affects the exciton-phonon interaction between the ZnO clusters and the zeolite host. The ZnO clusters exhibit a picosecond scale emission lifetime at room temperature.