Core-Shell Vanadium Oxide-Carbon Nanoparticles: Synthesis, Characterization, and Luminescence Properties Vilas G. Pol,* ,† Swati V. Pol, † Jose M. Calderon-Moreno, ‡ and A. Gedanken † Center for AdVanced Materials and Nanotechnology, Department of Chemistry, Bar-Ilan UniVersity, Ramat-Gan 52900, Israel, and Institute of Physical Chemistry ‘Ilie Murgulescu’, Academia Romana, 202 Splaiul Independentei, 060021 Bucharest, Romania ReceiVed: March 19, 2009; ReVised Manuscript ReceiVed: April 29, 2009 A single step, solvent-, catalyst-, and template-free synthesis process to prepare core-shell vanadium oxide-carbon nanoparticles from the dissociation of a single vanadium(V) oxytriethoxide precursor is demonstrated. The thermolysis of the VO(OC 2 H 5 ) 3 precursor in a closed reactor at 700 °C under autogenic pressure (450 psi) yielded carbon-coated V 2 O 3 (CVO) nanoparticles. Further thermal treatment of CVO in an air atmosphere at 450 °C for 2 h yielded V 2 O 5 nanoparticles (VON). The rhombohedral V 2 O 3 and orthorhombic V 2 O 5 crystal structures are confirmed by XRD measurement, supported by supplementary TEM and Raman spectroscopy measurements. The overall appearance of CVO and VON is studied by SEM, whereas the TEM distinguished the core-shell morphologies. The photoluminescence (PL) of vanadium oxide has been seldom studied before. The VON showed a room-temperature PL with a broad green emission, whereas the coated carbon in CVO lacks the green emission, revealing only a weak PL. Introduction Vanadium oxide has been in the forefront of applied research due to its important applications in optical switching, optical recording, and sensors. 1 Among all vanadium oxides (V 2 O 5 , V 2 O 3 ,V 3 O 5 , VO 2 , and VO), V 2 O 5 is the most stable form, possessing a unique high oxidation state that could be used as an amphoteric oxide and oxidizing agent. 2 Thick films of V 2 O 5 are employed as antistatic protection layers in the photographic industry, charge-storage material in lithium-ion and magnesium- ion batteries, 3 catalysts, 4 and electrochromic devices 5 and used for quality control in the food industry 6 and medical diagnosis 7 due to redox-dependent properties arising as a result of multiple valence states of vanadium. Nanoscale devices of any material systems exhibit unique chemical, electronic, and thermal proper- ties due to high surface area. Only a small fraction of the species adsorbed near the grain boundaries is enough to modify the electrochemical properties. 8 Additionally, V 2 O 5 is used as one of the cathode materials in rechargeable metal-ion batteries; for example, Li-ion batteries are lightweight and offer higher energy density with more stored energy per unit volume. 9,10 The core-shell V 2 O 5 -carbon nanocomposite is of special interest since it could insert/de-insert Li ions reversibly in nonaqueous Li salt solutions at a capacity close to the theoretical value in the 2-4 V potential range (270 mA h g -1 , corresponding to the insertion of 2 Li per V 2 O 5 ) with higher rates. 11 The high utilization of the active mass is due to the coated carbon, which enables good electrical contact between the particles. 11 Optical absorption and transmittance 12 of V 2 O 5 have been also inves- tigated in connection with its electrochromic properties. How- ever, studies on the luminescence properties of vanadium oxide materials are limited. 13 Thus, the fabrication of V 2 O 3 and V 2 O 5 nanostructures and the study of their optical properties are of importance. Vanadium sesquioxide (V 2 O 3 ) is a typical Mott insulator showing a metal-insulator transition near a critical tempera- ture. 14 Additionally, V 2 O 3 powder is frequently used in conduc- tive polymer composites and in catalysts. 15 Different V 2 O 5 nanostructures are produced by various methods, such as pellet formation by powder compaction, 16 thin films by thermal evaporation, 17 pulsed laser deposition, 18 nanoparticles by ball milling, 19 hydrothermal synthesis, 20 and nanorods by sol-gel 21 and reverse micelle 22 techniques. The synthesis of spherical V 2 O 3 nanoparticles by the reductive 23 pyrolysis of ammonium oxovanadium(IV) carbonato hydroxide and thermal decomposi- tion of divanadium pentoxide 24 to yield V 2 O 3 nanocrystallites has been reported. This article is solely focused on the synthesis of carbon-coated V 2 O 3 (CVO) from the thermal decomposition of single vana- dium(V) oxytriethoxide precursor employing a solvent-free process. The thermolysis (700 °C) of the VO(OC 2 H 5 ) 3 precursor in a closed autoclave created 450 psi pressure, which yielded carbon-coated V 2 O 3 during segregation of the dissociated molecules. Further thermal treatment of CVO in an air atmosphere at 450 °C for 2 h yields V 2 O 5 nanoparticles (VON). The VON showed a room-temperature PL with a broad green emission, whereas CVO lacks PL. The as-prepared CVO and VON have been systematically characterized to determine their morphology, structure, and composition. Experimental Section Vanadium(V) oxytriethoxide [VO(OC 2 H 5 ) 3 , (95%)] was purchased from Sigma-Aldrich and used as received. In a typical synthesis of CVO, 1.5 g of VO(OC 2 H 5 ) 3 was introduced in a 5 mL SS (stainless steel) reactor at room temperature in an inert atmosphere. The 1 / 2 in. diameter SS union part is initially sealed at one end using a cap. The partially filled SS reactor with * To whom correspondence should be addressed. E-mail: vilaspol@ gmail.com. † Bar-Ilan University. ‡ Institute of Physical Chemistry ‘Ilie Murgulescu’, Academia Romana. J. Phys. Chem. C 2009, 113, 10500–10504 10500 10.1021/jp902503w CCC: $40.75  2009 American Chemical Society Published on Web 05/21/2009