Synthesis and optical absorption properties of LaxCe1-xB6 submicron powders

Abstract

According to original knowledge, lanthanum hexaboride (LaB6) as an excellent thermionic electron emitter is characterized by a low work function, a high emission density, and a high brightness. Recently, much attention has been drawn to its another excellent optical properties: strong light absorption in near infrared rays (NIR), and transparency in visible light (VL), which result from the free electron plasmon resonance. However, up to now the optical properties and syntheses of ternary rareflearth hexaborides have been very rarely reported in the literature. In this paper, ternary LaxCe1-xB6 submicron crystallines are successfully synthesized using a solid-state reaction, in which La2O3 and CeO2 are used as rareflearth sources and NaBH4 as boron sources in a continuous vacuum condition. Effects of La doping content on the LaxCe1-xB6 phase composition, microstructure, and optical absorption properties are investigated by X-ray diffraction, scanning electron microscope (SEM), and transmission electron microscope (TEM). It is found that all the synthesized samples are composed of CaB6-type single-phase alloy with a space group Pm3m at the reaction temperature of 1200 ℃ held by 2 h. The SEM results indicate that the cubic-shaped ternary LaxCe1-xB6 crystals with a mean size of 200 nm are obtained and the energy dispersive spectrometer results confirm that the La atoms are randomly distributed at the lattice sites of CeB6. High resolution transmission electron microscope images refleal the single-crystalline nature, and the FFT pattern indicates the lattice fringe d=0.42 nm which agrees well with the (100) crystal plane. EDS analysis of TEM also indicates the La element has been doped into CeB6. And the optical absorption result shows that the absorption valley of CeB6 is 62 nm. With increasing La doping content to x=0.6 and 0.8, the absorption valleys of La0.6Ce0.4B6 and La0.8Ce0.2B6 decrease to 613 and 610 nm respectively indicating the blueshifts of the wavelength of absorption valley From the view point of practical application, the tunable characteristic of LaxCe1-xB6 may extend the optical applications in improving the efficiency of organic photovoltaics, replacing the expensive gold and silver nanoparticles, which may have a good usage in optical filters.