Controllable synthesis and upconversion emission of ultrasmall lanthanide-doped Sr2GdF7 nanocrystalsby Lijun Xiang, Guozhong Ren, Yifu Mao, Jin He, Rui Su

Optical Materials


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em e a l of nive

Sr2GdF7 nanocrystal


White-color s c r so s (N ion size distribution. The average crystalline size of the products can be controlled less than 10 nm. The energy transfer UC mechanisms for the fluorescent intensity were also investigated. Following Yb3+, r highl as bee ocryst multifunctional nanoscale carriers for integrated imaging and therapy [4–6]. b-NaYF4 is considered to be the most important host material due to its highest UC efficiency among all the hosts of

UC materials [7], but the size of b-NaYF4 NPs can hardly be tuned to sub-10 nm [8–11]. The smaller crystal size of UCNCs usually means weaker UC emission intensity, so, how to synthesize out synthesis of inescent p ion (LSS) m esize man of inorganic NCs, as well as many organic nanoparticles [25] method, many factors affect the phase structure, crystal siz phology and shape of UCNC including pH-value, doping, r temperature and time, the dosage of solvent and solute with their relative quantity and the type and dose of surfactant etc. [26].

Sr2GdF7 NCs possess good stability and have high UC efficiency compared to some other fluorides that have been reported previously. Pure tetragonal phase Sr2GdF7 NCs could be easy to be synthesized by LSS method, and the size of Sr2GdF7 NCs could be tuned⇑ Corresponding author.

E-mail address: (G. Ren).

Optical Materials 49 (2015) 6–14

Contents lists availab

Optical M .e lupconversion emission makes UCNCs as promising probes for biomedical imaging with attractive features, such as no autofluorescence from biological samples, large penetration depth [3], tumor-targeted imaging, vascular imaging, cell tracking, and even [24]. However, there are only a few reports ab ultrasmall Sr2GdF7 nanocrystals and its photolum tyes [32–35]. The method of liquid–solid–solut reported by Li has been extensively used to synth 0925-3467/ 2015 Elsevier B.V. All rights reserved.roperethod y kinds . In this e, moreactionunique narrow photoluminescence with high energy when excited by continuous-wave near-infrared light [3]. Among them, lanthanide doped inorganic nanocrystals (NCs) were chosen as one of the major objects for the potential boilogical application because they possess good stability, are free of toxicity and have high upconversion (UC) luminescence properties compared to some organic dyes and semiconductor quantum dots [4,5]. The special

Alkaline-earth fluorides (MF2, M = Ca, Sr, and Ba, fluorite phase) and LnF3 are promising host materials for luminescent lanthanide ions [12,14–16]. and so the alkaline-earth rare-earth fluorides with affirmed stoichiometric composition, such as BaYF5 [15,17–19],

Ba2LaF7 [20], BaGdF5 [21] and Sr2LaF7 [22]. The photoluminescent properties of Sr2GdF7 NCs were investigated in glass ceramics [23], and the UC properties of Sr2GdF7: Yb/Er NCs were studied1. Introduction

During past decades, the search fo luminescent fluorescent materials h [1,2]. Rare-earth upconversion nanEr3+, Tm3+ and Ho3+ ions doping, the Sr2GdF7 NCs show intense green, yellow, and white-color UC emission under the excitation of a 980 nm laser, and the doping concentration of lanthanide ions was optimized, which makes the NCs show maximum intensities under the excitation of a 980 nm laser.  2015 Elsevier B.V. All rights reserved. y emitting and efficient n a hot research field als (UCNCs) exhibit a sub-10 nm UCNCs with intense UC emission for biomedical imaging always be challenging [12,13].

Fluorides are more attractive as UC host materials than traditional oxide-based systems owing to their low vibrational energies, high chemical stability and versatile synthetic strategies [8,9,31].Keywords: sion (UC) emission properties of the products were investigated. The results reveal that apropos Gd ions content (0.30–0.45 mmol) is favorable to the formation of pure phase Sr2GdF7 NCs with more uniformControllable synthesis and upconversion lanthanide-doped Sr2GdF7 nanocrystals

Lijun Xiang a,b, Guozhong Ren a,b,⇑, Yifu Mao a,b, Jin H aHunan Key Laboratory for Micro-Nano Energy Materials and Devices, Faculty of Schoo bKey Laboratory of Low Dimensional Materials and Application Technology, Xiangtan U a r t i c l e i n f o

Article history:

Received 27 July 2015

Received in revised form 12 August 2015

Accepted 14 August 2015 a b s t r a c t

The effect of rare-earth ion system were studied unde phase Sr2GdF7 nanocrystal ligands. The effects of react journal homepage: wwwission of ultrasmall ,b, Rui Su b

Physics and Optoelectronics, Xiangtan University, Xiangtan 411105, Hunan, China rsity, Ministry of Education, Xiangtan 411105, China ontent on the phase structure, crystal size and morphology of SrF2–GdF3 lvothermal conditions. By tuning the molar ratio of reactants, tetragonal

Cs) were synthesized via solvothermal method using oleic acid as capping conditions on the phase structure, crystal size, morphology, and upconver3+ le at ScienceDirect aterials sevier .com/locate /optmat to less than 10 nm by changing some conditions. We also found that with appropriate lanthanide ions doping, the Sr2GdF7 NCs show intense UC emission under the excitation of a 980 nm laser.

These advantages make Sr2GdF7 NCs can be considered to be a kind of important host materials, and the ultrasmall Sr2GdF7 NCs with intense multicolor UC have potential applications in multicolor three-dimensional display devices, fluorescent labels for biomedical imaging and miniaturized solid-state light sources.

Furthermore, Sr2GdF7 NCs were synthesized via solvothermal method using oleic acid as capping ligands, which is very simple, environmentally friendly and well dissolved in cyclohexane. In the paper, we describe the synthesis of lanthanide-doped Sr2GdF7

NCs with LSS method. Pure ultrasmall Sr2GdF7 NCs can be successfully synthesized by manipulating the content of Gd3+ and Sr2+, and the influence of rare-earth ions content on the phase structure, crystal size and morphology of SrF2–GdF3 system were investigated. The upconversion emission color of Sr2GdF7 NCs can be readily tuned through lanthanide ions doping, and the UC luminescence mechanism has also been discussed in detail. 2. Experimental 2.1. Materials