Synthesis, characterization and exploration of the NIR luminescent properties in HfO2: Er, HfO2:Tm and HfO2:Er/Tm films photochemically prepared

The photolysis of the Hf(dbm)4, Er(dbm)3 and Tm(dbm)3 complexes on silicon substrates results in the production of pure HfO2, HfO2/Er, HfO2/Tm, and HfO2/Er/Tm films. The photochemistry of these complex precursors was monitored using UV–Visible and FT-IR spectroscopy. Under 254-nm light photolysis, the ligands were detached from the complexes, leading to the release of metal ions. These ions gradually oxidized and formed the respective oxide. Subsequently, the resulting films were calcined at 600 °C for 2 h to achieve complete oxidation and crystallinity. To characterize selected samples, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM-EDX) were employed. NIR luminescent studies revealed that when excited at 980 nm, the HfO2/Er samples exhibited emissions corresponding to the 4I13/2 → 4I15/2 transitions of the Er3+ ions. Conversely, the HfO2/Tm samples displayed emissions attributed to the 3H4 → 3F4 and 3F4 → 3H6 transitions of the Tm ions. In the case of HfO2 co-doped with Er/Tm, some of these emissions overlapped, resulting in a broadband centered at 590 nm. To explain the observed emissions, a mechanism based on energy transfer processes between both activators (Tm ↔ Er) has been proposed.