Near-Infrared Absorption of Monodisperse Silver Telluride (Ag2Te) Nanocrystals and Photoconductive Response of Their Self-Assembled Superlattices

摘要

Silver telluride nanocrystals (Ag2Te NCs) have been an enigma showing an anomalous growth process, yielding unusual structure and optical response. ~ Ag2Te is a little explored member in the silver chalcogenide family that possesses interesting physical properties including a transition from semiconductor to ionic conductor6 and large magnetrore-sistance in nonstoichiometric samples. Ag2Te exhibits high electron mobility and low thermal conductivit,y which are desirable for thermoelectric applications.9 This physics becomes richer when studied at the nanoscale dimensions comparable to the natural derealization lengths of the electronic and thermal excitations. Syntheses of Ag2Te nanowires, nanotubes, nano-rods, and nanoparticles~(1-3) have been reported. Although we have synthesized a range of Ag2Te NC sizes, we focused here on the optical and optoelectronic properties of monodisperse 3.1 nm Ag2Te NCs which uniquely exhibit a sharp optical absorption feature at 1154 nm. This wavelength is of particular interest as it falls in a window of transparency for biological tissue. The energy of the optical resonance shows a strong negative linear temperature dependence but unlike other semiconductor NCs the energy is not tunable with size. These NCs also differ from noble metal NCs where me plasmonic peak shifts as a function of the dielectric constant of the surrounding medium. These robust spectral responses could enable the use of Ag2Te NCs as a temperature reporter ' or a transducer ' of infrared energy in biological tissues and chemical environments free of complications stemming from spectral shifts due to the surrounding dielectric constant.