  Selective spectral detection of ultraviolet (UV) radiation is highly
important across numerous fields from health and safety to industrial and
environmental monitoring applications. Herein, we report a non-toxic,
visible-blind, inorganic quantum dot (QD)-based sensing scheme that expands the
spectral coverage of Silicon CMOS sensors into the UV, enabling efficient UV
detection without affecting the sensor performance in the visible and UV-band
discrimination. The reported scheme employs zinc magnesium oxide (ZnMgO) QDs
with compositionally tunable absorption across UV and high photoluminescence
quantum yield (PLQY) in the visible. The efficient luminescence and large
stokes shift of these QDs have been exploited herein to act as an efficient
downconverting material that enhances the UV sensitivity of Si-photodetector
(Si-PD). A Si-PD integrated with the QDs results in a nine-fold improvement in
photoresponsivity from 0.83 mA/W to 7.5 mA/W at 260 nm. Leveraging the
tunability of these QDs we further report on a simple UV band identification
scheme, using two distinct band gap ZnMgO QDs stacked in a tandem architecture
whose spectral emission color depends on the UV-band excitation light. The
downconverting stack enables facile discrimination of UV light using a standard
CMOS image sensor (camera) or by the naked eye and avoids the use of complex
optics.
