Transport Property of Upconversion Luminescence in Er/Yb Doped One-Dimensional NaYF4 Microcrystals
WANG Dan1, GAO Dang-li1*, DAI Hui-li2, ZHAO Dan1, LIANG Yu-qian1, WU Jia-ling1, ZHAO Jin1, ZHANG Chun-ling1
1. School of Science, Xi’an University of Architecture and Technology, Xi’an 710055, China
2. Physics Experiment Center, Engineering University of PAP, Xi’an 710086, China
Abstract：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.
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