Thermal Annealing Effects in Vanadium Pentoxide Films Intercalated with Eu 3+
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H.P. OLIVEIRA *t, J.M. ROSOLEN +, P.S. CALEFI t, C.A. BRUNELLO# AND C.F.O. GRAEFF # .Departamento de Quimica, FFCLRP/Universidade de Sao Paulo, Ribeirao Preto, SP, CEP 14040-901, Brazil. (*[email protected]) #Departamento de Fisica e Matematica, FFCLRP/Universidade de Sao Paulo. ABSTRACT This work reports on the spectroscopic properties of europium ions intercalated in a vanadium pentoxide matrix, as well as the effects of thermal treatment on its structural and electronic properties. X-ray diffraction, TG/DTA, ESR, luminescence as well as XANES were used in order to characterize the intercalation compound. For the as grown samples, the intercalation of Eu3 • is observed to have little effect in the V 20 5 lamellar structure, however the inter-planar spacing grows from 1.19 nm to 1.33nm for a 10% Eu3 content. The luminescence for the as grown samples are dominated by the host, the same happening with the ESR spectra. However ESR data show that the presence of Eu3 • in the host induces the partial reduction of vanadium to V4 -. For samples treated above 873K the luminescence excitation spectra presents a new shoulder at 300 nm, which when excited shows emissions bands typical of the Eu3". In ESR the same thermal treatments are marked by the appearance of a new broad line assigned to ferromagnetic EuO, as well as the partial oxidation of V4- to V5-. This result may be correlated to suppression of Eu3 " luminescence due to the presence of water in the neighborhood of Eu3 ". INTRODUCTION As a result of its potential use in a variety of applications vanadium pentoxide films have been extensively investigated [1-3]. The hydrated oxide can be generated by sol-gel process and
exhibits a layered structure which is suitable for host-guest intercalation chemistry with a variety of species (e.g. polyaniline, [M(bpy) 3]2, complexes, alkali-metal ions and porphyrins), retaining its basic integrity during the course of reactions [4-7]. In fact, vanadium oxide bronzes MKV 205 can be synthesized by sol-gel process with promising applications as rechargeable cathodic material in secondary lithium batteries and electrochromic devices [3,8]. The chemical and physical properties of the lanthanide compounds have been used in heterogeneous catalysts, ceramics materials and in opto-electronic applications. [9,10]. The present work reports the spectroscopic properties of europium ions intercalated in a vanadium pentoxide matrix, as well as the effects of thermal treatment on its structural and opto-electronic properties. EXPERIMENTAL Preparative procedure The preparation of vanadium pentoxide via sol-gel processing has been reported in the literature [11]. The V20 5.1.8H 20 films were obtained by the slow evaporation of the V2 0 5 gel on a glass plate at room temperature (297 K) and in air. The intercalation compounds were obtained by reacting the vanadium pentoxide films deposited on a glass plate with small portions of a 0,01M aqueous solution of the EuCli. The mixture was allowed to stand at room 137 Mat. Res. Soc. Symp. Proc. Vol.
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