TITLE : f-f–Like d-d Transitions for NIR Emission

ABSTRACT :

Sharp near-infrared (NIR) emitters, particularly those operating in the NIR-II window (1000–1700 nm), hold promise for applications in telecommunications, lasers and high- resolution in vivo imaging. Such sharp NIR emissions at a few specific wavelengths arise from shielded electronic transitions in rare-earth lanthanides like Yb^3+ , Nd^3+ and Er^3+. In contrast, transitions typically yield broad emission, because d-electrons strongly interact with the surrounding ligands. In this talk, I will discuss about atomic-scale structure-function link showing how Mo 3+ doped in Cs2NaInCl6 double perovskites yield electronic transitions emitting ultra-narrow NIR-II radiation, similar to the transitions. Recently, we reported the first ambient-stable Mo^3+ based ultra-narrow (FWHM <10 meV) NIR-II emission at 1095 nm. [1,2] The highly symmetric [MoCl 6 ] 3- octahedra with 4d 3 electrons, result into intra-configurational spin-flip (ICSF) transitions. Likewise, d-2 electrons in tetrahedral lattice, like Mn 5+ -doped into an oxide lattice also show ICSF transitions with ultra-narrow emission at ~1170 nm. The ICSF transitions behave similar to atomic-like transitions, with ultra-narrow spectral width, violation of Kasha’s rule, and showing upconversion photoluminescence. [3]

Reference:
1. A. Ghosh, S. Saikia, S. Mukherjee, E. Johannesson, H. Rensmo, A. Nag, Angew. Chem. Int. Ed. 2025, e202415003.
2. A. Nag, A. Ghosh, S. Saikia, Indian Patent Provisional Application (202521097969), 2025.
3. S. Saikia, A. Ghosh, A. Nag, ACS Energy Lett. 2026 (accepted).

ABOUT THE SPEAKER :

Prof Angshuman Nag is a Professor of Chemistry at IISER Pune, India. He did his Ph. D. from IISc Bangalore in 2009, and subsequently completed two terms as a postdoctoral researcher. He started his research group at IISER Pune in the year 2012. His research is focused on developing novel semiconductors like halide perovskites and colloidal quantum dots for optoelectronic applications. Prof Nag is a Fellow of Indian Academy of Sciences Bengaluru. He received SwarnaJayanti Fellowship from Government of India. He is currently an Associate Editor of the journal JACS Au.

MEETING DETAILS :

Speaker: Prof Angshuman Nag, Department of Chemistry, Indian Institute of Science Education and Research (IISER), Pune

Venue: A4 conference room, South Campus, IIT Mandi

Date and Time: March 14, 2026, Monday at 11:00 AM