Professional Education

  • Doctor of Philosophy, Jilin University (2015)

Current Research and Scholarly Interests

I mainly focus on the electrical transport and optical properties of low-dimensional materials at extreme conditions, such as ultra-high pressure, low temperature, high magnetic-fields.

All Publications

  • Tuning Optical and Electronic Properties in Low-Toxicity Organic-Inorganic Hybrid (CH3NH3)3Bi2I9 under High Pressure. The journal of physical chemistry letters Zhang, L., Liu, C., Lin, Y., Wang, K., Ke, F., Liu, C., Mao, W. L., Zou, B. 2019: 1676–83


    Low-toxicity, air-stable methylammonium bismuth iodide (CH3NH3)3Bi2I9 has been proposed as a candidate to replace lead-based perovskites as highly efficient light absorbers for photovoltaic devices. Here, we investigated the effect of pressure on the optoelectronic properties and crystal structure of (CH3NH3)3Bi2I9 up to 65 GPa at room temperature. We achieved impressive photoluminescence enhancement and band gap narrowing over a moderate pressure range. Dramatic piezochromism from transparent red to opaque black was observed in a single crystal sample. A structural phase transition from hexagonal P63/ mmc to monoclinic P21 at 5.0 GPa and completely reversible amorphization at 29.1 GPa were determined by in situ synchrotron X-ray diffraction. Moreover, the dynamically disordered MA+ organic cations in the hexagonal phase became orientationally ordered upon entering into the monoclinic phase, followed by static disorder upon amorphization. The striking enhancement of conductivity and metallization under high pressure indicate wholly new electronic properties.

    View details for PubMedID 30905153

  • Phase transformations of Al-bearing high-entropy alloys AlxCoCrFeNi (x=0, 0.1, 0.3, 0.75, 1.5) at high pressure APPLIED PHYSICS LETTERS Wang, C., Tracy, C. L., Park, S., Liu, J., Ke, F., Zhang, F., Yang, T., Xia, S., Li, C., Wang, Y., Zhang, Y., Mao, W. L., Ewing, R. C. 2019; 114 (9)

    View details for DOI 10.1063/1.5079868

    View details for Web of Science ID 000460820600017

  • Mechanosensitive upconverting nanoparticles for visualizing mechanical forces in vivo Lay, A., Siefe, C., Fischer, S., Mehlenbacher, R., Das, A., Nekimken, A., Ke, F., Mao, W., Pruitt, B., Cohen, B., Alivisatos, P., Goodman, M., Dionne, J. AMER CHEMICAL SOC. 2018
  • Bright, Mechanosensitive Upconversion with Cubic-Phase Heteroepitaxial Core-Shell Nanoparticles. Nano letters Lay, A. n., Siefe, C. n., Fischer, S. n., Mehlenbacher, R. D., Ke, F. n., Mao, W. L., Alivisatos, A. P., Goodman, M. B., Dionne, J. A. 2018


    Lanthanide-doped nanoparticles are an emerging class of optical sensors, exhibiting sharp emission peaks, high signal-to-noise ratio, photostability, and a ratiometric color response to stress. The same centrosymmetric crystal field environment that allows for high mechanosensitivity in the cubic-phase (α), however, contributes to low upconversion quantum yield (UCQY). In this work, we engineer brighter mechanosensitive upconverters using a core-shell geometry. Sub-25 nm α-NaYF4:Yb,Er cores are shelled with an optically inert surface passivation layer of ∼4.5 nm thickness. Using different shell materials, including NaGdF4, NaYF4, and NaLuF4, we study how compressive to tensile strain influences the nanoparticles' imaging and sensing properties. All core-shell nanoparticles exhibit enhanced UCQY, up to 0.14% at 150 W/cm2, which rivals the efficiency of unshelled hexagonal-phase (β) nanoparticles. Additionally, strain at the core-shell interface can tune mechanosensitivity. In particular, the compressive Gd shell results in the largest color response from yellow-green to orange or, quantitatively, a change in the red to green ratio of 12.2 ± 1.2% per GPa. For all samples, the ratiometric readouts are consistent over three pressure cycles from ambient to 5 GPa. Therefore, heteroepitaxial shelling significantly improves signal brightness without compromising the core's mechano-sensing capabilities and further, promotes core-shell cubic-phase nanoparticles as upcoming in vivo and in situ optical sensors.

    View details for PubMedID 29927609