Syntheses of optically efficient (La 1  x  y Ce x Tb y )F 3 nanocrystals via a hydrothermal method Qiang Wang a , Yumin You b , Richard D. Ludescher b , Yiguang Ju a,n a Department of Mechanical & Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA b Department of Food Science, Rutgers University, New Brunswick, NJ 08901, USA article info Article history: Received 1 March 2009 Received in revised form 21 January 2010 Accepted 26 January 2010 Available online 1 February 2010 Keywords: Fluorescence lifetime Hydrothermal Lanthanide fluoride Nanomaterials Photoluminescence Quantum yield UV nanophosphors X-ray nanophosphors abstract Optically efficient cerium and terbium doped lanthanide fluoride (La 1 x y Ce x Tb y )F 3 nanocrystals with different doping concentrations have been synthesized by a hydrothermal route in the presence of ethylenediamine tetraacetic acid disodium salt (EDTA). The results showed that the formation of nanocrystals with different morphologies depends on terbium ion Tb 3+ doping concentration, but independent of cerium ion Ce 3+ doping concentration. With increase in Tb 3+ doping concentration, the morphologies of nanocrystals evolved from a spherical shape to a plated-like one. In addition, both the photoluminescence quantum yield (PL QY) and the fluorescence lifetime of nanocrystals increased with the increase in Ce 3+ doping concentration in cerium and terbium co-doped system. The PL QY reached up to 55%, and the lifetime up to 7.3 ms. Transmission electron microscopy (TEM), X-ray diffraction (XRD), selected area electron diffraction (SAED), X-ray fluorescence (XRF), energy dispersive spectro- scopy (EDS), ultraviolet–visible (UV–vis) absorption, photoluminescence (PL) and infrared (IR) spectroscopies were employed to characterize the properties of nanocrystals. The growth mechanism of nanocrystals with different morphologies and optical properties of nanocrystals with different doping concentrations were investigated. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Lanthanide doped nanocrystals have drawn increasing re- search attention due to their various attractive applications in field emission displays [1,2], optical telecommunications [3], novel optoelectronic devices [4], solar cells [5,6], blue LED-based solid state lighting [7–9], and biological labeling [10–12]. Especially, due to the concerns of toxicity and optical instability of quantum dots and organic dye molecules used as biomarkers, lanthanide doped fluorescent nanocrystals have become promis- ing alternative materials due to their superior physical and chemical properties for applications in immunoassay, cell ima- ging, and photodynamic therapy (PDT) [10–14]. In PDT studies, recent research has demonstrated that rare earth doped up- conversion NaYF 4 nanocrystals can be used to convert low-energy infrared light to high-energy visible light to activate photosensi- tizers to produce singlet oxygen, which can kill cancer cells [14]. In the past decades, lanthanide doped down-conversion nanocrystals with different host matrixes such as fluoride, phosphate, orthovanadate, and oxides have been synthesized [15–29]. Among them, the rare earth doped lanthanum fluoride (LaF 3 ) nanocrystals have received a particular attention because lanthanum fluoride matrix has much lower vibrational energy (  350 cm 1 ) than other host matrixes and less non-radiative quenching via phonon relaxation [30]. Furthermore, LaF 3 exhibits superior thermal and environmental stabilities and is considered as an ideal host materials for various rare earth ions doped phosphors [18]. However, one of the main challenges for rare earth ion doped phosphors is the energy conversion efficiency. To enhance energy conversion efficiency and photoluminescence quantum yield (PL QY), some nanocrystals with core/shell structure have been synthesized to reduce the energy loss arising from non-radiative quenching, which undoubtedly increases the complexity of the synthetic process of nanomaterials [17,22,25]. In addition, synthesis of optically efficient nanocrystals with a narrow size distribution in a desired size range is another challenge. To date, many approaches have been developed to synthesize down-conversion fluoride nanocrystals with various doped lanthanide ions such as Eu 3+ , Nd 3+ , Ho 3+ , Tb 3+ , Ce 3+ , and Er 3+ [15–22]. These methods include the co-precipitation approach [16,19,22], the polyol method [17], the hydrothermal method [18], and organometallic thermolysis [31]. For X-ray and deep ultraviolet (UV) based PDT technique, Ce 3+ and Tb 3+ co-doped fluoride nanocrystals are among the best choices because of their excellent excitation spectrum in the UV and the X-ray spectral ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2010.01.028 n Corresponding author. Tel.: + 1 609 258 5644; fax: + 1 609 258 6233. E-mail address: yju@princeton.edu (Y. Ju). Journal of Luminescence 130 (2010) 1076–1084