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Solid State Cooling Materials
There is always a demand for an alternative to conventional refrigeration techniques that rely on pollutant gases or unsustainable gas sources, such as Helium. Solid state cooling devices can be applied as more efficient, inexpensive, and versatile cooling equipment. This can reduce our dependence on Helium and be used as a nanofridge to cool quantum computers. Solid state cooling materials are mainly based on thermoelectric, magnetocaloric, and elastocaloric effects. Our research interests are focused on discovering novel low-temperature thermoelectric materials and new ferroelectric materials (Figure 1). In addition to cooling, another related application is using low-temperature thermoelectric materials to power wearable electronics. Utilizing the human body, a constant energy source, to generate electrical power through low-temperature thermoelectric materials!
2. Nonlinear Optical Materials
The Jedi in the Star Wars universe have a dream, the rainbow laser sword (Figure 2 top). That is the same dream of scientists and industry, generating lasers of as many different frequencies as possible. One applicable technique is using nonlinear optical (NLO) materials to upconvert frequencies of incoming lasers based on the second-harmonic generation effect (Figure 2 bottom). Our research efforts are focused on discovering novel NLO materials. We are particularly interested in ultraviolet-NLO (UV-NLO) and infrared-NLO (IR-NLO) materials applied in the deep ultraviolet (<200 nm) and infrared regions (2-20 μm) respectively. NLO materials require a number of criteria: (1) first and most critical, non-centrosymmetric crystal structure (NCS); (2) suitable band gap for good transmission at the required spectrum region; (3) large second-harmonic generating (SHG) coefficients; (4) high laser damage threshold (LDT); (5) moderate birefringence; (6) excellent stability including thermal-, chemical- and air-stability and enough mechanical properties; (7) ability to grow large high optical quality single crystals. It is challenging to simultaneously fulfill all seven of these attributes. There are several parameters that are intrinsically inversely proportional. For example, a larger band gap can both result in a lower SHG signal and a higher LDT, while introducing structural complexity can both promote an NCS and raise the barrier for crystal growth. We will combine structural chemistry, crystal growth, and defect chemistry to design new materials which can fulfill all the seven attributes! Hard, but possible.
3. Photocatalytic Degradation of Organic Pollutants
The rapid population and economic growth demands more energy, but also generates more pollutants. Just check your surrounding and read the news! Compared to other environmental pollution, organic compounds are not easily removed with conventional methods. Using novel semiconductors as a photocatalyst to decompose toxic organic compounds to non-hazardous products is a promising solution. The photocatalytic degradation process is powered by UV-or Visible-light, which are the unlimited generous gifts from the sun. Our research will be focused on exploring efficient, sustainable, and cheap photocatalysts for the decomposition of organic pollutants.
