Quantum dot-layered double hydroxide composites for near-infrared emitting codes

Near-infrared (NIR)-emitting PbS-based quantum dots (QDs) and exfoliated layered double hydroxide (LDH) nanosheets were self-assembled to form photostable composites for NIR-emitting codes. PbS QDs prepared by a pyrolysis synthetic method or PbS-CdS (core-shell) QDs prepared by a cation exchange using PbS QDs were transferred to aqueous solutions by surface ligand exchange to dihydrolipoic acid (DHLA). The DHLA-decorated QDs and exfoliated LDH nanosheets were assembled by electrostatic interactions during vortexing. The QD-LDH composite films prepared by drop-casting exhibit more than 500% higher NIR PL intensities than the counterpart QD films (without LDH matrices) under identical conditions (i.e., QD concentration). Photostability tests under continuous light irradiation reveal that the PbS-CdS QD films are more photostable than the PbS QD films. Formation of the QD-LDH composites gives rise to further enhancement in the photostability of the film. The photostable PbS-CdS QD-LDH composite films were used to create novel NIR-emitting codes. NIR fluorescence images of a pattern of two kinds of PbS-CdS QD-LDH composite films were recorded with an InGaAs CCD camera equipped with optical filters

The H+ related defects involved in domain reversal for both near-stoichiometric and heavily Mg-doped lithium niobate crystals

Domain reversal was performed on both near-stoichiometric and heavily Mg-doped lithium niobate crystals. H+ related defect structures in these two types of crystals were studied through the infrared absorption spectra. It is found that the intensity of some decomposed peaks of absorption band change apparently during domain reversal for near-stoichiometric lithium niobate crystals but not for heavily Mg-doped lithium niobate crystals. According to these experimental results, distinct models about H+ related defect structure in LiNbO3 lattice were supposed for them. Nb4+Li and Mg3-Nb were considered as the centers of H+ related defect complex for near-stoichiometric and heavily Mg-doped lithium niobate crystals respectively. Different behavior of them was used to explain the difference of infrared absorption spectra during domain reversal between two types of crystals. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005