Luminescent nanocrystals in the rare-earth niobate–zirconia system formed via hydrothermal method

Luminescent nanocrystals based on the rare-earth niobates (Ln3NbO7, Ln=Y, Eu) and zirconia (ZrO2) that were composed of 50mol% Ln3NbO7 and 50mol% ZrO2, were hydrothermally formed as cubic phase under weakly basic conditions at 240°C. The lattice parameter of the as-prepared nanoparticles corresponding to the composition of Y3−xEuxNbO7–4ZrO2 that was estimated as a single phase of cubic gradually increased as the content of europium x increased. The existence of small absorbance peaks at 395 and 466nm corresponding to the Eu3+7F0→5L6, and 7F0→5D2 excitation transition, respectively, was clearly observed in the diffuse reflectance spectra of the as-prepared samples containing europium. The optical band gap of the as-prepared samples was in the range from 3.5 to 3.7eV. The photoluminescence spectra of the as-prepared nanocrystals containing europium showed orange and red luminescences with main peaks at 590 and 610nm, corresponding to 5D0→7F1 and 5D0→7F2 transitions of Eu3+, respectively, under excitation at 395nm Xe lamp. The emission intensity corresponding to 5D0→7F2 transition increased as heat-treatment temperature rose from 800 to 1200°C. This graphical abstract shows the excitation and emission spectra and a transmission electron microscopy image of nanocrystals (with composition based on the rare-earth niobates (Ln3NbO7, Ln=Y, Eu) and zirconia (ZrO2) that were composed of 50mol% Ln3NbO7 and 50mol% ZrO2) formed via hydrothermal route. [Display omitted] •Nanocrystals composed of 50mol% Y3−xEuxNbO7 and 50mol% ZrO2 was directly formed.•The nanocrystals were hydrothermally formed under weakly basic conditions at 240°C.•The Y3NbO7 showed an UV-blue and broad-band emission under excitation at 240nm.•The emission is originated from the niobate octahedral group [NbO6]7−.•The nanocrystals showed orange and red luminescences (5D0→7F1 and 5D0→7F2 , Eu3+).