Short-Wave Infrared Emissions from Te4+-Ln(3+) (Ln: Er, Yb)-Codoped Cs2NaInCl6 Double Perovskites

A Cs2NaInCl6 double perovskiteis environmentallybenign, and its wide band gap (& SIM;5.1 eV) makes it photoinactiveand photostable in the ultraviolet, visible, and short-wave infrared(SWIR) regions. Interestingly, the octahedrally coordinated In3+ lattice site is suitable for doping lanthanide ions likeEr(3+) and Yb3+, which can emit SWIR radiationat 1540 nm (0.805 eV) and 994 nm (1.247 eV), respectively. But theoptical excitation of lanthanides is Laporte forbidden, and the hostrequires excitation energy >5.1 eV. The large Stokes shift fortheexcitation and SWIR emission reduces the power conversion efficiency.Here, we codoped Te4+ with Er3+ or Yb3+ into Cs2NaInCl6. Te4+ absorbs atthe sub-band-gap level at around 3.1 eV (400 nm) because of 5s(2) & RARR; 5s(1)5p(1) electronic transitions.Then, the excited Te4+ transfers its energy nonradiativelyto an Er3+ or Yb3+ codopant. The de-excitationof Er3+ or Yb3+ through f-f electronictransitions emits SWIR radiation at 1540 and 994 nm, respectively,along with weak visible-light emissions. Temperature (8-300K) dependent photoluminescence excitation, emission, and lifetimemeasurements reveal the mechanism of these energy transfer processes.Finally, we fabricated a simple phosphor-converted light-emittingdiode (pc-LED) emitting SWIR radiation.

Automated summary

The environmentally benign Cs2NaInCl6 double perovskite has a wide band gap of about 5.1 eV, making it photocatively and photostable in the UV, visible, and SWIR regions. By doping lanthanide ions like Er3+ and Yb3+ into the octahedrally coordinated In3+ lattice site, SWIR radiation at 1540 nm and 994 nm can be emitted. However, the optical excitation of lanthanides is Laporte forbidden, and the host requires excitation energy >5.1 eV. To overcome this limitation, Te4+ was codoped with Er3+ or Yb3+ to transfer energy and emit SWIR radiation. Temperature-dependent measurements revealed the mechanism of energy transfer processes. A pc-LED emitting SWIR radiation was successfully fabricated.