We report x-ray luminescence from LaF3:Ce3+,Tb3+ and LaF3:Tb3+ water-soluble nanoparticles. The x-ray luminescence is dominated by emission from Tb3+ ions, similar to photoluminescence spectra of the nanoparticle aqueous solutions and spectra from nanoparticle powders precipitated from the aqueous samples. Coating the nanoparticles with an insulating inorganic LaF3 or organic H2N–(CH2)10–COOH layer can enhance the x-ray luminescence from the aqueous nanoparticles. This enhancement is most likely due to the decreased energy loss due to the particle-solvent interactions.

Terahertz properties of chemically synthesized MgO nanocrystals are studied by terahertz time-domain spectroscopy in the frequency range extending up to 3.7 THz. The experimentally determined optical and dielectric properties of the nanocrystalline MgO are compared with those of a bulk MgO single crystal. Three prominent resonance modes, which are essentially responsible for the dielectric properties of the nanostructured MgO in the terahertz regime, are characterized at ω 1 /(2π) ) 4.26 THz, ω 2 /(2π) ) 7.68 THz, and ω 3 /(2π) ) 12.18 THz and are well-described by a multiple-oscillator model through theoretical fitting. The MgO nanocrystals may find intriguing applications in developing terahertz quasi-optic components and terahertz spectroscopy.