Ionic to Electronic Conductivity Studies of Lithium-Borate Ruby-Glass-Ceramics Containing Gold Nano Particles

Abstract

Glass-ceramics containing Au nanoparticles have been synthesized in the glass composition 30Li 2 O-70B 2 O 3 with HAuCl 4 .3H 2 O as dopant. The characteristic ruby colour has been observed which is attributed to the surface plasmon resonance of the Au nanoparticles, uniformly embedded in the glass matrix. The imparted red colour due to the presence of gold nanoparticles has been confirmed by studying the optical absorption spectra using UV-VIS spectrometer in the visible range (400-1000 nm) which show a characteristic absorption peak at ~560 nm. In order to check the crystallization/ amorphous nature, the samples were powdered and characterized using X-ray diffraction (XRD). The microstructural modifications in the samples due to the addition of Au have been recorded using scanning electron microscopy (SEM). Further, the electron spin resonance (ESR) studies reveal that the electronic state of gold is either Au 0 or Au + . AC conductivity studies have been performed at room temperature over a frequency range 100 to 10 MHz. The ac conductivity data is fitted by Almond-West law with power exponent 's'. The dc conductivity is found to be increasing with the increase of temperature for a typical ruby glass, but almost constant with dopant concentration.[Keywords : Ruby-glass, Gold nanoparticles, Optical absorption, SPR, Transport properties] IntroductionRuby glasses containing gold nanoparticles or other noble metal nanoparticles have been extensively investigated for the past decades because of their excellent properties such as ultrafast optical response and large third order non-linear susceptibility. [1][2][3][4] This kind of glasses are expected to be promising materials for ultrafast optical switches and optical circuits with micrometer size. Hence, preparation and characterization of materials containing noble metal nanoparticles is the most challenging task for researchers in the area of materials science. Glasses containing metal nanoparticles look very distinctive with different colours. Since the quantum size effects and enhanced surface effects are expected to influence the electronic and optical properties at much smaller particle sizes, it leads to more interest for researchers to fabricate the metal nanoparticles in glasses. 5,6 Such investigated gold-ruby glasses are used not only as decorative glasswares but also for many technological applications in the field of electrical and optical communications. Silicate ruby glasses are synthesized mainly by using HAuCl 4 .3H 2 O along with a reducing agent, such as tin based compounds, and then annealing the glass for several hours at a particular temperature. 7,8 Metal nanoparticles in glasses are also precipitated using electron beam and laser irradiation. In these methods the metal ions are reduced but need thermal treatment.