Oct 13, 2011
High-temperature sensing with quantum dots
Research on the temperature-dependent properties of quantum dots has centred on the detection of low-energy states of these structures in the 10–300 K temperature range. However, for applications such as optoelectronics, this temperature is probably too low. To realize quantum dot-based optoelectronic devices, the behaviour of these nanomaterials at elevated temperatures is of practical importance. Researchers in the US have studied the issue and their investigation pushes the boundary of thermal sensing using highly luminescent quantum dots.
To prepare the material, cadmium selenide/zinc sulphide (CdSe/ZnS) quantum dots are loaded into a high-temperature resistant SiO2 dielectric matrix. The CdSe/ZnS:SiO2 nanocomposite was solution fabricated to yield thermally stable thin films. The room-temperature optical absorption is measured and the temperature dependence of the photoluminescent emission is investigated from 295 to 525 K. The emission peak wavelength Stokes shifts and the full width at half maximum increases with temperature.
As shown in the figure, the quantum dot bandgap is 2.04 eV. Atomic force microscopy (AFM) of the thin film reveals a cluster distribution with a 3.6 nm average particle size. The temperature-dependent spectral shift of the photoluminescence under thermal cycle enables self-referenced intensity-based temperature measurements with 0.11 nm/oC sensitivity.
The next steps include optimization of the CdSe/ZnS:SiO2 material system and characterization of the high-temperature response via optical spectroscopy. The CdSe/ZnS:SiO2 nanocomposite can be applied in combination with other luminescent indicators for multi-sensing applications using the same immobilization chemistry. This research demonstrates the potential for new possibilities in quantum dot-based optoelectronic devices such as luminescence-based thermal sensors.
The researchers presented their results in the journal Nanotechnology.
About the author
Devin Pugh-Thomas is a PhD student in electrical engineering with an emphasis in materials science at the University of Virginia. She performed the film fabrication and optical spectroscopic measurements. Dr Brian M Walsh is a physicist in the Laser Remote Systems Branch at NASA Langley Research Center, Hampton, VA. His interests include spectroscopy, new luminescence materials and lasers for remote sensing. Dr Mool C Gupta is a Langley Professor and Director of NSF I/UCRC Center for Lasers and Plasmas at the University of Virginia, Charlottlesville, VA. His research interests include laser processing of materials, photovoltaics, nanomaterials and sensors.