Revealing Interplay of Defects in SnO2 Quantum Dots for Blue Luminescence and Selective Trace Ammonia Detection at Room Temperature.

Defect chemistry in SnO2 is well established for resistive sensors but remains to be elusive for photoluminescence (PL) sensors. It demands a comprehensive understanding of the role of cationic and oxygen defects as well as the creation of abundant such defects to provide a selective PL signal. To accomplish it, SnO2 quantum dots (QDs ∼ 2.4 nm) are prepared without a capping agent along with other dimensions. Then, the relationship of defects with the blue-emission PL is unfolded by electron energy loss spectroscopy, lifetime measurements, X-ray absorption, and Raman spectroscopic measurements. The defects acting as Lewis acid sites are utilized for selective ammonia detection. Huge enhancements of the obscured blue luminescence at 2.77 and 2.96 eV from the SnO2 QDs are observed because of interaction with ammonia. The linear variation of PL intensities with analyte concentrations and the recovery of the sensor are elaborated with detection up to 5 ppm. The interplay of defects in SnO2 is further established theoretically for site-specific interactions with ammonia by density functional theory (DFT) calculations. Thus, the unique mechanism revealed for the superlative performance of the PL sensor with uncapped SnO2 QDs provides a novel platform for defect-engineering-based optoelectronic applications.