Proceedings of MATSUS Fall 2024 Conference (MATSUSFall24)
DOI: https://doi.org/10.29363/nanoge.matsusfall.2024.247
Publication date: 28th August 2024
Phosphor converted light emitting diodes (pc-LEDs) have revolutionized solid-state white lighting by replacing energy-inefficient filament-based incandescent lamps. However, such energy inefficient tungsten halogen lamps still remain the source for ultrabroad near-infrared (NIR) radiation. It is primarily because of lack of rational approach to design ultrabroad NIR emitting phosphors hence their scarcity. To address this issue, we rationale a host halide perovskite with self-trapped exciton (STE) emission that can merge with dopant emission due to d-d transitions. The host STE emission covers NIR-1 and also provides the π-donor ligand Cl⁻ that significantly reduces the energy of dopant d-d transitions emitting in the NIR-II. Thereby, we developed W4+-doped and Mo4+-doped Cs2(NaAg)BiCl6 perovskites emitting ultrabroad NIR radiation with unprecedented spectral widths of 434 and 468 nm, respectively. Upon band-edge excitation, the soft lattice of the host exhibits broad STE emission covering NIR-I (680 nm), which then nonradiatively excites the dopants leading NIR-II emission with a peak at ~950 nm via d-d transitions. Vibronic coupling broadens the dopant emission. A combination of large spin-orbit coupling, Jahn-Teller distortion (d2 electronic configuration), and the distortion due to the heterovalent replacement of Bi3+ by W4+ or Mo4+ lead to intense NIR photoluminescence with quantum yield ~40%. The composite of our ultrabroad NIR phosphors with biodegradable polymer could be processed into free-standing films and 3D printed structures. Large (170 × 170 mm2), robust, and thermally stable 3D printed pc-LED panels emit ultrabroad NIR radiation, demonstrating NIR imaging applications.
This work is supported by Science & Engineering Research Board (SERB, CRG/2022/001199 and SB/SJF/2020-21/02) India; Department of Science and Technology (FIST program, SR/FST/CS-II/2019/105) India, Prime Minister's Research Fellowship (PMRF), Ministry of Education, India. The authors would like to thank Dr. Wolfgang Caliebe for assisting with EXAFS measurements at the beamline P64, DESY. Financial support by the Department of Science and Technology, India, provided within the framework of the India@DESY collaboration is gratefully acknowledged.
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