Hydrothermal synthesis of ZnO–TiO2:Yb3+/Ho3+ phosphor heterostructures for upconversion luminescence applications

Zinc oxide–titanium dioxide heterostructure phosphors doped with ytterbium and holmium ions were synthesized using a hydrothermal method. The structure, morphology, and upconversion luminescence properties of the prepared heterostructures were investigated. The mixed oxides of ZnO and TiO2 (anatase and rutile) were confirmed by x-ray diffraction. Electron microscopy revealed agglomerated spherical particles with nanoscale dimensions. Diffuse reflectance spectra exhibited several absorption bands at 453, 488, 540, and 647 nm. Optical absorption bands were associated with electronic transitions of holmium ions, and codoping increased the estimated optical bandgap energy. Under excitation at 980 nm, visible emission peaks at 545 and 661 nm were observed. The composition containing 0.1 mol. % holmium and 9 mol. % ytterbium showed the highest emission intensity and good luminescence stability, indicating potential for near infrared to visible light conversion applications. These results demonstrate that zinc oxide–titanium dioxide heterostructures doped with rare earth ions are promising materials for efficient near-infrared to visible light conversion.