Abstract:
Phosphor converted light emitting diodes (pc-LEDs) have revolutionized solid-state white lighting by replacing energy-inefficient filament-based incandescent lamps. However, such a pc-LED emitting ultrabroad near-infrared (NIR) radiations still remains a challenge, primarily because of the lack of ultrabroad NIR emitting phosphors. To address this issue, we have prepared 2.5 percent W sup(4+)-doped and 2.8 percent Mo sup(4+)-doped Cs sub(2)Na sub(0.95)Ag sub(0.05)BiCl sub(6) 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 self-trapped exciton (STE) emission covering NIR-I (700?nm), which then nonradiatively excites the dopants. The Pi -donor ligand Cl sup(-) reduces the energy of dopant d-d transitions emitting NIR-II with a peak at Tilde 950 nm. Vibronic coupling broadens the dopant emission. The large spin-orbit coupling and local structural distortion might possibly enhance the dopant emission intensity, leading to an overall NIR photoluminescence quantum yield Tilde 40 percent. The composite of our ultrabroad NIR phosphors with biodegradable polymer polylactic acid could be processed into free-standing films and 3D printed structures. Large (170 x 170 mm sup(2)), robust, and thermally stable 3D printed pc-LED panels emit ultrabroad NIR radiation, demonstrating NIR imaging applications.
