Doping ns2 -Ions and Lanthanide Ions in Metal-Halide Perovskites: Visible to Short-Wave Infrared Emission

Abstract

Lead halide perovskites are being extensively explored in recent times for their promising optoelectronic properties. However, lead toxicity and structural stability impose some limitations for their wide spread commercial applications. Lead free halide double perovskites are proposed as alternatives to lead halide perovskites. But the lead free halide double perovskites lack the interesting semiconducting and optical properties of lead based perovskites. Interestingly, the halide double perovskites have intriguing structural properties such as octahedral sites and compositional tunability, that can make double perovskites a promising class of host materials for doping luminescent centers. Lanthanide ions with narrow emission feature are promising emitters, especially for short-wave infrared emission (900- 1700 nm). We realized that In3+ ions in Cs2AgInCl6 double perovskite have similar ionic radii and oxidation state compared to lanthanide ions, and therefore, Er3+- and Yb3+ -doped Cs2AgInCl6 are prepared emitting 1540 and 990 nm radiation, respectively. However, the samples required to be excited at wavelength below 350 nm. The large energy difference between excitation and emission causes a large energy loss, even for an ideal luminescence efficiency. This thesis explores the potential of halide double perovskites to host lanthanide luminescent centers and reduces the energy difference between the excitation and emission by codoping ns2-ions like Bi3+, Sb3+, Te4+. Another related lead free system is Cs2SnCl6 vacancy ordered perovskite, that has electronically isolated [SnCl6]2- octahedral. Doping Bi3+ and Sb3+ in Cs2SnCl6 provides opportunity to study the optical properties of luminescent centers in isolated octahedrons unlike the corner shared octahedrons in double perovskites. With the help of temperature dependent photoluminescence spectroscopy, we find the mechanistic origin of excitation and emission processes in Bi3+- and Sb3+ -doped Cs2SnCl6.