稀土掺杂上转换(upconversion, UC)发光材料是一种把两个或多个长波长、 低能量的近红外光子转换成一个短波长、 高能量的可见或紫外光子的发光材料。 由于其锐线发射、 长寿命和无背底荧光等特性, 在生物成像、 检测与治疗、 太阳能电池、 药物输送和光催化等诸多领域具有极大的应用价值。 目前, NaYF4∶Yb3+/Er3+微/纳晶体是公认的最重要的上转换发光材料之一, 其相关的上转换发光机理、 制备方法、 光谱调制以及实际应用方面均已被科学家们进行了大量的研究。 然而, 荧光效率低这一严重问题一直制约着上转换发光材料实际应用的进程。 另外, 关于单颗粒上转换NaYF4∶Yb3+/Er3+微/纳晶体中荧光的产生、 输运和耦合特性还不清楚。 一维微/纳材料作为一种二维受限体系, 为研究电子和光子的输运特性提供了一个理想模型。 通过柠檬酸钠辅助的水热法合成了长径比可控的一维NaYF4∶Yb3+/Er3+微米棒和一维NaYF4∶Yb3+/Er3+@NaYF4∶Yb3+/Tm3+核-壳棒结构。 采用激光共聚焦激发系统, 在单颗粒一维NaYF4∶Yb3+/Er3+微米棒中, 通过控制棒的长径比、 激发方式和制备特殊的核-壳结构等方式, 研究了荧光的产生和同步荧光图案, 揭示了在一维棒结构中荧光光线的输运模式为: 垂直于棒轴方向的荧光沿棒横截面的戒指形谐振腔趋肤传播和近似沿棒轴方向的荧光在棒介质中反复全反射以波导方式输运至棒端后靶向输出; 在NaYF4∶Yb3+/Er3+@NaYF4∶Yb3+/Tm3+核-壳一维棒结构中, 在单一波长激发下, 获得了源自单颗粒的Tm3+的蓝色和Er3+绿色特征发射。 采用点激发方式激发一维核-壳微米棒样品一端时, 呈强烈蓝色荧光空间不对称的哑铃状分布, 且中间出现了微弱绿色荧光, 构筑出单颗粒单一波长激发下的局域色彩调制发射, 并为微量稀土发光中心局域掺杂的检测提供了一种途径。 在波导激发和点激发方式下, 在对单颗粒一维NaYF4∶Yb3+/Er3+和NaYF4∶Yb3+/Er3+@NaYF4∶Yb3+/Tm3+核-壳微米棒的荧光产生和输运的调制中, 实现了对离子荧光发射颜色的控制, 并揭示了荧光在一维棒中传输耦合过程中, 沿棒长模式荧光比沿径向模式荧光更容易传输耦合。 该研究的一维棒荧光的输运和耦合特性, 暗示了其在光子耦合器件、 上转换波导激光以及荧光成像方面的潜在应用。

Rare earth doped upconversion material is a luminescent material that converts two or more long-wavelength, low-energy near-infrared photons into one short-wavelength, high-energy visible or ultraviolet photon. Due to its sharp line emission, long lifetime and no background luminescence characteristics, it has great application value in many fields such as bio-imaging, detection and treatment, solar cell, drug delivery and photocatalysis. Among them, NaYF4∶Yb3+/Er3+ micro/nanocrystal is one of the most important upconversion materials, and there is a lot of research in upconversion luminescence mechanism, preparation method, spectral modulation and practical application. However, low luminescence efficiency is still a bottleneck that restricts various practical applications. In addition, the transport and coupling properties of a single NaYF4∶Yb3+/Er3+ micro/nanocrystal are unclear. One-dimensional micro/nanomaterial is a restricted system in two dimensions. Therefore, it provides an ideal model for studying the transport properties of electrons and photons. In this study, one-dimensional NaYF4∶Yb3+/Er3+ microcrystals and NaYF4∶Yb/Er@NaYF4∶Yb/Tm core-shell structure microcrystals with controllable length to diameter ratio are synthesized by the hydrothermal method assisted by sodium citrate. The laser confocal excitation system is used to study the generation of luminescence and synchronous luminescent pattern in a single one-dimensional NaYF4∶Yb3+/Er3+ microrod by controlling the length to diameter ratio of the rod, the excitation mode and the preparation of special core-shell structures. It reveals that in one-dimensional rod structure, the transport mode of luminescence is: luminescence that is perpendicular to the direction of the rod axis skin-spreads along the ring-shaped cavity of the cross section of a rod, luminescence approximately along the axis of the rod targetedly transports to a rod end with total reflection waveguiding approach. In the one-dimensional NaYF4∶Yb3+/Er3+@NaYF4∶Yb3+/Tm3+ core-shell rod structure, a single-particle functional material that is excited by single wavelength with local multicolor light emitting is constructed. It also provides a way for the detection of local doping of traced rare earth luminescence centers. We have achieved the controllable emission colors in the modulation of luminescence generation and transport in single-particle one-dimensional NaYF4∶Yb3+/Er3+ and NaYF4∶Yb3+/Er3+@NaYF4∶Yb3+/Tm3+ core-shell microrods in waveguide-excitation mode and point-excitation mode. Moreover, we also reveal that luminescence spreading along the rod length mode is easier to couple than that spreading along the radial mode. The properties of luminescence transport and coupling in one-dimensional microrods suggest their potential applications in photonic coupling devices, upconversion waveguide lasers and luminescence imagings.