Abstract:
Short-wave infrared (SWIR) radiation (700 to 1700 nm) is important for applications in bio-imaging, security camera, food inspection, remote-sensing, and optical fiber communication. Epitaxially grown III-V semiconductors are common choice for SWIR light emitting diodes (LEDs), but with limitations in mass production and high expense. Therefore, the development of suitable SWIR emitters, particularly the broadband ones, remains a significant challenge. This thesis focuses on designing broadband SWIR emitters by doping metal halide double perovskites like Cs2NaInCl6. Such a host provides suitable octahedral coordination for potential SWIR emitting dopants, and are stable, environmentally benign.
In chapter 2, we designed Sb3+-Ln3+ (Ln = Er, Yb) codoped Cs2NaInCl6 showing SWIR emission at 997 nm and 1540 nm, for f-f transitions of Yb3+ and Er3+, respectively. But the spectral width of f-f transitions is typically narrow. So, for achieving broadband SWIR emission, we doped transition metal ions with d-d transitions in chapter 3 and 4. Broad dual emitter covering white-light emission and SWIR emission was achieved by codoping Bi3+ and Cr3+. Thereafter, we achieved ultrabroad SWIR emitters with unprecedented FWHM of ~450 nm, by doping W4+ or Mo4+ in Cs2Na0.95Ag0.5BiCl6 double perovskite. Chapter 5 explores the synthesis of colloidal nanocrystals these double perovskites. To understand the optical excitation, emission and energy transfer processes, detailed spectroscopic investigations including temperature dependent (6-300 K) photoluminescence have been carried out. Subsequently, phosphor converted (pc) LEDs of these materials have been fabricated and studied in detail. As a proof of concept, we fabricated prototype pc-LED panels with more than 100 pc-LEDs demonstrating their capability for SWIR imaging, and inspecting food freshness.
