Nanocrystalline Eu-doped PrB6 hexaborides with tunable optical absorption: A combined experimental and density functional theory study

Nanocrystalline Eu-doped PrB6 ultrafine powders have been successfully fabricated through solid-state chemical reaction of Eu2O3, PrCl3 and NaBH4 as raw materials. The optical absorption properties of the synthesized samples were investigated by experimental measurement and theoretical calculation. As a result, a strong red-shift of transmittance wavelength of nanocrystalline PrB6 is achieved via altering the Eu doping. Theoretically, the doping of divalent Eu into trivalent PrB6 reduces the plasma frequency excitation energy and increases the corresponding transmittance wavelength. Additionally, the synchrotron radiation absorption shows that Pr and Eu atoms exist in the form of Pr3+ in PrB6 and Eu2+ in EuB6, and X-ray photoelectron spectroscopy results also indicate that Eu exists in the state of Eu2+ in the nanocrystalline Pr0.4Eu0.6B6, which confirms that the Eu doping reduces the number of conduction electrons in PrB6 and decreases the plasma frequency excitation energy.