Tunable and High Photoluminescence Quantum Yield from Self‐Decorated TiO2 Quantum Dots on Fluorine Doped Mesoporous TiO2 Flowers by Rapid Thermal Annealing

Herein a novel approach is reported to achieve tunable and high photoluminescence (PL) quantum yield (QY) from the self‐grown spherical TiO2 quantum dots (QDs) on fluorine doped TiO2 (F‐TiO2) flowers, mesoporous in nature, synthesized by a simple solvothermal process. The strong PL emission from F‐TiO2 QDs centered at ≈485 nm is associated with shallow and deep traps, and a record high PL QY of ≈5.76% is measured at room temperature. Size distribution and doping of F‐TiO2 nanocrystals (NCs) are successfully tuned by simply varying the HF concentration during synthesis. During the post‐growth rapid thermal annealing (RTA) under vacuum, the arbitrary shaped F‐TiO2 NCs transform into spherical QDs with smaller sizes and it shows dramatic enhancement (≈163 times) in the PL intensity. Electron spin resonance (ESR) and X‐ray photoelectron spectroscopy (XPS) confirm the high density of oxygen vacancy defects on the surface of TiO2 NCs. Confocal fluorescence microscopy imaging shows bright whitish emission from the F‐TiO2 QDs. Low temperature and time resolved PL studies reveal that the ultrafast radiative recombination in the TiO2 QDs results in highly efficient PL emission. A highly stable, biologically inert, and highly fluorescent TiO2 QDs/flowers without any capping agent demonstrated here is significant for emerging applications in bioimaging, energy, and environmental cleaning. Tunable wavelength and high photoluminescence (PL) quantum yield from ligand‐free TiO2 quantum dots (QDs) self‐grown on fluorine doped TiO2 flowers is demonstrated here. This study offers new insight in understanding the mechanism of ultrahigh PL emission by the fluorine‐doped TiO2 (F‐TiO2) QDs decorated on mesoporous F‐TiO2 flowers.