Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Ga3+ Doping Induced Simultaneous Size/Shape Control, Enhanced Red Upconversion Luminescence, and Improved X‑ray Imaging of ZnO:Yb/Tm for Multifunctional Nanoprobes Yuemei Li,† Rui Wang,*,† Wei Zheng,† and Yongmei Li*,‡ †
School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150001,China Key Laboratory of Hormones and Development (Ministry of Health), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital & Tianjin Institute of Endocrinology, Tianjin Medical University, 300070 Tianjin, China
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ABSTRACT: We report that the efficient Ga3+-doped ZnO:Yb/Tm (7/0.5 mol %) upconversion nanoparticles (UCNPs) can simultaneously control size/shape and enhance red upconversion luminescence (UCL) by transition-metal Ga3+ doping. The dynamic decay time reveals that the intensity of red upconversion luminescence increases with increasing Ga3+ content. Furthermore, upconversion nanoparticles are fabricated through silica layer with Stöber method. The lung of mouse with the ZnO:Ga/Yb/Tm@ SiO2 injection can be readily visualized using X-ray imaging, which will influence the field of biological probe based on UCNPs@SiO2.
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INTRODUCTION In recent years, the search for high efficiency, sensitivity, and resolution for fluorescence imaging has been occurring in increasingly active fields such as biomedicine and biological probes.1−5 The near-infrared (NIR; 700−1000 nm) is generally considered as the “optical transmission window” of the biological tissues owing to their high tissue penetration depth.6,7 Moreover, the NIR radiation has no negative influence on organelles and cell function, comparing with traditional UV radition. Lanthanide (Ln = Yb, Tm, Er, and Ho) codoped upconversion nanoparticles (UCNPs) have been a promising fluorescence material for bioimaging, due to their unique energy upconversion luminescence (UCL) capabilities.8 UCNPs can convert the NIR to visible light by energy transfer, which indicates that UCNPs can be indirectly excited by NIR light. Therefore, the UCNPs can significantly decrease thermal loading and minimize the tissue damage.9−13 The use of UCNPs for the biological appliations has received increasing attention. However, as an optimal biological probe, the high UCL efficiency and multicolor UCL output are simultaneously required for UCNPs, which is still a challenge.14,15 It is wellknown that the UCL efficiency is related to particle size, crystallite phase, dopant ions, and host system.16−18 In addition, size, shape, and phase of UCNPs have also great influence on their luminescence and biological application.19−22 Compared with the sulfide hosts and fluoride hosts, oxide systems were addressed as the efficiency UCL hosts, owing to their high chemical stability and low toxicity.23−25 Currently studies on host of UCNPs have been focused on diverse oxide-based materials such as Y2O3 or Gd2O3.26,27 In © XXXX American Chemical Society
particlular, ZnO has the low toxicity and hexagonal structures. It is reported that the hexagonal phase is benefical for UCL emission.28,29 Moreover, as a semiconductor, the exciton Bohr radius of ZnO is larger than that of insulators, resulting in pronounced quantum confinement effect for nanoparticles. Therefore, the UCL properties of Ln3+ doped in semiconductor nanoparticles can be tailored thourgh size/shape control or bandgap change, which have attracted great interest in fabricating a biogical probe and bioimaging applications.30,31 However, it is still a challenge to successfully achieve incorporation of Ln3+ into the lattices of ZnO semiconductor nanoparticles. There is a large discrepancy of ionic radius and charge between Ln3+ and ZnO host materials. In addition, most of UCNPs doped with Yb/Tm generally performed blue UCL emission, which reduced their application in biological probe due to the tissue absorption of wavelengths less than 600 nm.32,33 Enhancing the red UCL efficiency in Yb/Tm codoped system is of utmost importance. A few reports have been related to realize the UCL emission in Ln3+ doped semiconduction system via metal ions doping, such as Mg2+ and Mn2+.34,35 For ZnO:Yb/Tm UCNPs, Ga3+ ions doped (
