Pb-free all-inorganic halide double perovskites (DPs) have emerged as an important class of environmentally benign phosphors for optoelectronic applications. The studies on them mainly restricted to the visible spectral region.
Lanthanide (Ln3+) doping is proposed as a valid approach to expand the spectral range of DPs towards the near-infrared (NIR) region.Unfortunately, these Ln3+-doped DPs still suffer from low weak NIR emission of Ln3+ due to the small absorption cross-section of Ln3+.
In a study published in Angewandte Chemie International Edition, the research group led by Prof. CHEN Xueyuan from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences developed a new class of NIR-emitting DPs based on Ln3+-doped Cs2(Na/Ag)BiCl6. Benefiting from the Na+-induced breakdown of local site symmetry in the Cs2AgBiCl6 DPs, efficient NIR emissions of Ln3+(e.g., Yb3+ and Er3+) are realized through Bi3+ sensitization.
The researchers first systematically studied optical properties of Ln3+-doped Cs2(Na/Ag)BiCl6 phosphors to determine the optimal Na+ content, and then comprehensively surveyed the excited-state dynamics and the energy transfer process in the optimal Ln3+-doped Cs2Ag0.2Na0.8BiCl6 phosphors by means of temperature-dependent steady-state and transient photoluminescent spectroscopy.
Raman spectroscopy analysis and first-principles density functional theory (DFT) calculations confirmed that Na/Ag alloying caused the change of Bi-Cl bond length, which resulted in the local symmetry breaking of Bi3+ in [BiCl6]3- octahedron.
Compared with the Na-free Cs2AgBiCl6 counterparts, the NIR emission of Yb3+ and Er3+ can be boosted by 7.3-fold and 362.9-fold in Cs2Ag0.2Na0.8BiCl6 DPs, with the optimal photoluminescence quantum yields (PLQYs) of 19.0% and 4.3%, respectively.
Besides, the researchers employed these Ln3+-doped NIR-emitting Cs2Ag0.2Na0.8BiCl6 DPs for 365-nm UV-converted NIR light emitting diodes( LEDs), which indicated their potential applications as high-performance optoelectronic devices.
These findings provide new insight into the design of efficient NIR luminescent Ln3+ doped all-inorganic halide double perovskites materials, which may accelerate the development of new near-infrared optoelectronic devices.
Schematic of efficient NIR luminescence and luminescence mechanism in Cs2(Ag/Na)BiCl6:Ln3+ (Ln = Yb and Er) double perovskites (Image by Prof. CHEN's group)
Contact:
Prof. CHEN Xueyuan
Fujian Institute of Research on the Structure of Matter
Chinese Academy of Sciences
Email: xchen@fjirsm.ac.cn
