Preparation of quaternary tungsten bronze nanoparticles by a thermal decomposition of ammonium metatungstate with oleylamine

We report the synthesis of quaternary tungsten bronze nanocrystals (QTBN) doped with sodium and cesium, Na x Cs y WO z , which were prepared via a simple thermal decomposition process involving the combination of ammonium metatungstates with oleylamine as both the surfactant and the solvent. The QTBN capped with oleylamine had an average diameter of about 30 nm and exhibited a shielding property of approximately 97% of near-infrared radiation across a wavelength range of 780–2100 nm, while transmitting 64% of visible light at 432 nm upon dispersion in a non-polar solvent of toluene. Our characterizations showed that both sodium and cesium ions could successfully be intercalated into the framework of the cubic pyrochlore structure of tungsten oxide at a relatively low reaction temperature and within a short time, generating the quaternary compound of tungsten bronze nanoparticles. As a result, our procedure conferred near infrared absorption properties upon the QTBN that are superior to those of ternary tungsten bronze nanoparticles in terms of absorption range and intensity, suggesting a significantly advanced solution process capable of producing useful near infrared absorbents.