Importance of the Hierarchical Core@Multishell Nanostructure in Obtaining White Light Emission in Ln(III)-Doped ZrO2 Nanoparticles

The design of the hierarchically tailored 4.4 nm nanoparticles was based on the alternation between undoped and Ln(III)-doped layers (Ln(III) = Eu(III), Tb(III)), ensuring the isolation of different Ln(III) ions in order to prevent energy transfers between them, which may lead to long-term loss of quality of the emission due to one-sided cascading of the excitation energy to a single emitter. Photoluminescence emission and excitation spectra have shown the importance of this design in obtaining white light: for the alternating layer design there is no energy transfer between Tb(III) and Eu(III) ions, and emission spectra with lambda(exc) = 260 nm of Tb(III),Eu(III)-codoped ZrO2 nanoparticles over a ZnO-coated silica host show a combination of Tb(III) green, Eu(III) red, and silica defect blue emissions resulting in pure white emission, and warm white with an additional Eu(III)-doped layer. While the ZnO coating layer was vital in improving Eu(III) emission intensity by suppression of SiO2 surface (-OH) oscillators, nanoparticles constructed with gradually fewer features of the main hierarchical nanostructure resulted in Tb(III) -> Eu(III) energy transfers, and loss of fine control over the final emission color.