posted on 2024-02-05, 13:41authored byBarnali Mondal, Aparna Shinde, Parikshit Kumar Rajput, Habibul Arfin, Riteeka Tanwar, Prasenjit Ghosh, Angshuman Nag
In near-infrared (NIR)-emitting phosphors,
the emission typically
originates from forbidden d−d or f−f electronic transitions
of metal ion dopants. But the excitation happens through higher-energy
(UV or blue) allowed transitions, resulting in energy loss for this
UV- or blue-to-NIR conversion. Here we report Cs2MX6 (M = Mo/W, X = Cl/Br) 0D perovskite derivatives with NIR
excitation and emission arising from the same pair of d-electronic states, showing small Stokes shifts. The samples show
significant optical absorption at 787 nm (12700 cm−1) and emission at 986 nm (10140 cm−1) because of
the d2 electronic configuration of M4+ in isolated [MX6]2− octahedra.
Interestingly, isolated [MX6]2− also
leads to vibrational fine structures in the electronic excitation
and emission spectra at cryogenic temperatures, which are rare for
undoped inorganic crystals. Finally, phosphor-converted light-emitting
diodes are fabricated by coating Cs2MoCl6 on
commercial 730 nm LED chips without requiring UV-blue chips.