Tunable and High Photoluminescence Quantum Yield from Self‐Decorated TiO 2 Quantum Dots on Fluorine Doped Mesoporous TiO 2 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 TiO 2 quantum dots (QDs) on fluorine doped TiO 2 (F‐TiO 2 ) flowers, mesoporous in nature, synthesized by a simple solvothermal process. The strong PL emission from F‐TiO 2 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‐TiO 2 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‐TiO 2 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 TiO 2 NCs. Confocal fluorescence microscopy imaging shows bright whitish emission from the F‐TiO 2 QDs. Low temperature and time resolved PL studies reveal that the ultrafast radiative recombination in the TiO 2 QDs results in highly efficient PL emission. A highly stable, biologically inert, and highly fluorescent TiO 2 QDs/flowers without any capping agent demonstrated here is significant for emerging applications in bioimaging, energy, and environmental cleaning.