Synthesis of Compositionally Defined Single-Crystalline Eu3+-Activated Molybdate鈥揟ungstate Solid-Solution Composite Nanowires and Observation of Charge Transfer in a Novel Class of 1D CaMoO

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• 作者：Jinkyu Han ; Coray McBean ; Lei Wang ; Cherno Jaye ; Haiqing Liu ; Daniel A. Fischer ; Stanislaus S. Wong
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：February 19, 2015
• 年：2015
• 卷：119
• 期：7
• 页码：3826-3842
• 全文大小：961K
• ISSN：1932-7455

文摘

As a first step, we have synthesized and optically characterized a systematic series of one-dimensional (1D) single-crystalline Eu³⁺-activated alkaline-earth metal tungstate/molybdate solid-solution composite CaW_1鈥?i>xMo_xO₄ (0 鈮?鈥?i>x鈥?鈮?1) nanowires of controllable chemical composition using a modified template-directed methodology under ambient room-temperature conditions. Extensive characterization of the resulting nanowires has been performed using X-ray diffraction, electron microscopy, and optical spectroscopy. The crystallite size and single crystallinity of as-prepared 1D CaW_1鈥?i>xMo_xO₄:Eu³⁺ (0 鈮?鈥?i>x鈥?鈮?1) solid-solution composite nanowires increase with increasing Mo component (鈥?i>x鈥?. We note a clear dependence of luminescence output upon nanowire chemical composition with our 1D CaW_1鈥?i>xMo_xO₄:Eu³⁺ (0 鈮?鈥?i>x鈥?鈮?1) evincing the highest photoluminescence (PL) output at 鈥?i>x鈥?= 0.8, among samples tested. Subsequently, coupled with either zero-dimensional (0D) CdS or CdSe quantum dots (QDs), we successfully synthesized and observed charge transfer processes in 1D CaW_1鈥?i>xMo_xO₄:Eu³⁺ (鈥?i>x鈥?= 0.8)鈥?D QD composite nanoscale heterostructures. Our results show that CaW_1鈥?i>xMo_xO₄:Eu³⁺ (鈥?i>x鈥?= 0.8) nanowires give rise to PL quenching when CdSe QDs and CdS QDs are anchored onto the surfaces of 1D CaWO₄鈥揅aMoO₄:Eu³⁺ nanowires. The observed PL quenching is especially pronounced in CaW_1鈥?i>xMo_xO₄:Eu³⁺ (鈥?i>x鈥?= 0.8)鈥?D CdSe QD heterostructures. Conversely, the PL output and lifetimes of CdSe and CdS QDs within these heterostructures are not noticeably altered as compared with unbound CdSe and CdS QDs. The differences in optical behavior between 1D Eu³⁺ activated tungstate and molybdate solid-solution nanowires and the semiconducting 0D QDs within our heterostructures can be correlated with the relative positions of their conduction and valence energy band levels. We propose that the PL quenching can be attributed to a photoinduced electron transfer process from CaW_1鈥?i>xMo_xO₄:Eu³⁺ (鈥?i>x鈥?= 0.8) to both CdSe and CdS QDs, an assertion supported by complementary near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements.