• Physics and Astronomy Colloquium

December 5, 2025 3:30 PM - December 5, 2025 4:30 PM
PAIS 1100

Host:

Denis Selitskiy

Presenter:

Masaru Kuno (University of Notre Dame)

Video Recording

The optical refrigeration of a semiconductor remains an open goal in the area of condensed phase laser cooling. Although early reports have suggested cooling successes in various semiconductor nanostructures, a debate exists as to whether actual cooling was, in fact, achieved. This talk focuses on efforts we have made to demonstrate optical refrigeration in all-inorganic, CsPbBr₃ nanocrystals.  The particles are made using colloidal chemistry and exhibit near-unity emission quantum yields. We have further found that the paticles possess unusually large single-photon/multiple-phonon up-conversion efficiencies. Together, both suggest that cooling is possible with these materials. We go on to describe efforts made to demonstrate optical cooling. In tandem, we probe the microscopic origin of excitation up-conversion in these nanocrystals and posit the origin of their size-dependent Stokes shifts as well as the identity of the emitting state.

Professor Kuno leads an interdisciplinary nanoscience program focused on single-nanostructure spectroscopy and imaging. His group develops absorption and emission techniques to probe optical and electronic properties of quantum dots, nanowires, and 2D semiconductors, with applications to light-emitting materials, solar-energy conversion, photocatalysis, and challenges such as semiconductor optical refrigeration.

Kuno’s contributions have been recognized by honors including the Rev. Edmund P. Joyce Award for Excellence in Undergraduate Teaching, a Cottrell Teacher-Scholar Fellowship, and an NSF CAREER Award. His work bridges chemistry, materials science, and condensed-matter physics, offering insights into nanoscale processes that enable next-generation photonic and energy technologies.