Irfanullah Mir, Sharma Dharmendar Kumar, Chulliyil Ramya, Chowdhury Arindam
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India.
Dalton Trans. 2015 Feb 21;44(7):3082-91. doi: 10.1039/c4dt03249g.
Visible light excitable and color tunable ∼5% Eu(3+)-doped LaF3 nanocrystals (NCs), containing 9-oxidophenalenone ligands bound to the surface as visible light sensitizers for Eu(3+) dopants, have been synthesized by a facile solution-based method. The crystalline phase structure, size, composition, morphology and luminescence properties of the NCs are characterized using X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and steady-state and time-resolved emission spectroscopy. The results show that these NCs are very small in size (<10 nm), display high degree of crystallinity and have pure tysonite structure of LaF3 with P3[combining macron]c1 space group. The visible light excitation of the capping ligands triggers an alternate display of steady-state, short-lived blue emission (τ < 1 ns) and time-delayed, long-lived sensitized red Eu(3+) emission (τ = 0.41 ms), allowing photoluminescence chromacity tuning as a function of delay time within a specific inorganic composition. The visible light sensitization of the dopant Eu(3+) sites proves more efficient than direct excitation of 5% Eu(3+)-doped LaF3 NCs capped by citrate ligands. The dopant Eu(3+) ions are well protected from non-radiative deactivation through high-energy vibrations of the organic capping ligands which is proved by the long lifetime of the sensitized Eu(3+) emission. The time-resolved emission spectra collected over a period of several milliseconds reveal that the dopant Eu(3+) ions occupy at least three different sites in the NC host. It is further inferred that the sensitized Eu(3+) emission primarily comes from surface dopant sites and sites just underneath the surface of the NCs. We propose that some of the interior Eu(3+) sites also display sensitized emission, which are indirectly populated via Eu(3+) → Eu(3+) energy migration from surface-sensitized Eu(3+) sites of the NCs.
通过一种简便的溶液法合成了可见光激发且颜色可调的约5% Eu(3+)掺杂的LaF3纳米晶体（NCs），其表面含有与Eu(3+)掺杂剂结合的9-氧化菲醌配体作为可见光敏化剂。使用X射线衍射、高分辨率透射电子显微镜、能量色散X射线光谱以及稳态和时间分辨发射光谱对NCs的晶相结构、尺寸、组成、形态和发光特性进行了表征。结果表明，这些NCs尺寸非常小（<10 nm），具有高度结晶性，且具有纯的具有P3[combining macron]c1空间群的LaF3的钛钇矿结构。封端配体的可见光激发引发了稳态、短寿命蓝色发射（τ < 1 ns）和时间延迟、长寿命敏化红色Eu(3+)发射（τ = 0.41 ms）的交替显示，使得在特定无机组成内光致发光色度可作为延迟时间的函数进行调节。掺杂剂Eu(3+)位点的可见光敏化被证明比直接激发由柠檬酸盐配体封端的5% Eu(3+)掺杂的LaF3 NCs更有效。掺杂剂Eu(3+)离子通过有机封端配体的高能振动得到很好的保护，免受非辐射失活，这通过敏化Eu(3+)发射的长寿命得到证明。在几毫秒内收集的时间分辨发射光谱表明，掺杂剂Eu(3+)离子在NC主体中至少占据三个不同的位点。进一步推断，敏化Eu(3+)发射主要来自表面掺杂位点和NCs表面正下方的位点。我们提出，一些内部Eu(3+)位点也显示敏化发射，这些位点是通过NCs表面敏化的Eu(3+)位点的Eu(3+)→Eu(3+)能量迁移间接填充的。
