Publications
Journal Articles
Entropy-Driven Reversible Melting and Recrystallization of Layered Hybrid Perovskites
Published in Publications, 2024
Abstract: Typical layered 2D A2PbX4 (A: organic ammonium cation, X: Br, I) perovskites undergo irreversible decomposition at high temperatures. Can they be designed to melt at lower temperatures without decomposition? Which thermodynamic parameter drive the melting of layered perovskites? These questions are addressed by considering the melt of A2PbX4 as a mixture of ions (like ionic liquids), and hypothesized that the increase in the structural entropy of fusion (ΔSfus) will be the driving force to decrease their melting temperature. Then to increase structural ΔSfus, A-site cations are designed that are rigid in the solid crystal, and become flexible in the molten state. Different tail groups in the A-site cations form hydrogen-, halogen- and even covalent bonding-interactions, making the cation-layer rigid in the solid form. Additionally, the rotation of ─NH3+ head group is suppressed by replacing ─H with ─CH3, further enhancing the rigidity. Six A2PbX4 crystals with high ΔSfus and low melting temperatures are prepared using this approach. For example, [I−(CH2)3−NH2(CH3)]2PbI4 reversibly melts at 388 K (decomposition temperature 500 K), and then recrystallizes back upon cooling. Consequently, melt-pressed films are grown demonstrating the solvent- and vacuum-free perovskite films for future optoelectronic devices
Recommended citation: Parikshit Kumar Rajput, Parashurama Salunkhe, Manmayuri Sarma, Meghasree Basu, Animesh Gopal, Aprajita Joshi, Ajinkya Sundarnath Shingote, Surajit Saha, Atikur Rahman, and Angshuman Nag.
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Thermal Evolution of the Structure and Luminescence of the Hybrid-Cation-Stabilized
Published in ACS Publications, 2024
Abstract: A typical layered hybrid perovskite, A2PbBr4, consists of organic A-site cations and the inorganic [PbBr4]2– perovskite layers. Alternatively, here the A-site cation itself is a hybrid one, namely, [(4AMTP)PbBr2]22+, containing a nonperovskite PbBr2 type lattice and 4AMTP (4-aminomethyltetrahydropyran cation). How does this hybrid A-site cation influence the structure and luminescence of a [(4AMTP)PbBr2]2PbBr4 2D layered perovskite? Here, we address this question by exploring crystal structure and photoluminescence (PL) in the temperature range 7–300 K. Centimeter-sized single crystals of [(4AMTP)PbBr2]2PbBr4 show a stable monoclinic P21/c space group in the entire temperature range, without showing any phase transition. The absence of a phase transition signifies higher structural rigidity brought in by the hybrid A-site cation, unlike typical A2PbBr4 with organic A-site cations that often exhibit a phase transition in this temperature range. PL of [(4AMTP)PbBr2]2PbBr4 at room temperature shows excitonic emissions similar to a typical A2PbBr4 with an organic A-cation because neither hybrid nor organic A-site cations contribute to the valence and conduction band edges. Interestingly, below 70 K, the excitonic emission suddenly red-shifts by 15 meV from 3.017 to 3.002 eV, along with an order of magnitude increase in lifetime. Similar temperature-induced PL changes in monoclinic-phase layered perovskites were previously attributed to spin-forbidden “dark” exciton emissions, which become significant at lower temperatures. The hybrid A-site cation in [(4AMTP)PbBr2]2PbBr4 stabilizes its monoclinic phase, influencing its luminescence characteristics. The hybrid A-site cations offer exciting prospects for tailoring the chemical composition, structure, and properties of layered perovskites, warranting the novel properties of halide perovskites.
Recommended citation: Ajinkya Sundarnath Shingote, Taniya Dutta, Parikshit Kumar Rajput, and Angshuman Nag.
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Short-Wave Infrared Emissions from Te4+–Ln3+ (Ln: Er, Yb)-Codoped Cs2NaInCl6 Double Perovskites
Published in ACS Publications, 2023
Abstract: A Cs2NaInCl6 double perovskite is environmentally benign, and its wide band gap (∼5.1 eV) makes it photoinactive and photostable in the ultraviolet, visible, and short-wave infrared (SWIR) regions. Interestingly, the octahedrally coordinated In3+ lattice site is suitable for doping lanthanide ions like Er3+ and Yb3+, which can emit SWIR radiation at 1540 nm (0.805 eV) and 994 nm (1.247 eV), respectively. But the optical excitation of lanthanides is Laporte forbidden, and the host requires excitation energy >5.1 eV. The large Stokes shift for the excitation and SWIR emission reduces the power conversion efficiency. Here, we codoped Te4+ with Er3+ or Yb3+ into Cs2NaInCl6. Te4+ absorbs at the sub-band-gap level at around 3.1 eV (400 nm) because of 5s2 → 5s15p1 electronic transitions. Then, the excited Te4+ transfers its energy nonradiatively to an Er3+ or Yb3+ codopant. The de-excitation of Er3+ or Yb3+ through f–f electronic transitions emits SWIR radiation at 1540 and 994 nm, respectively, along with weak visible-light emissions. Temperature (8–300 K) dependent photoluminescence excitation, emission, and lifetime measurements reveal the mechanism of these energy transfer processes. Finally, we fabricated a simple phosphor-converted light-emitting diode (pc-LED) emitting SWIR radiation.
Recommended citation: Habibul Arfin, Radha Rathod, Ajinkya Sundarnath Shingote, K. R. Priolkar, Pralay K. Santra, and Angshuman Nag.
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Conferences
Emerging Materials 2023
Published in IISER Pune, 2024
This conference is is aimed to cover contemporary research findings on the classes of materials including low dimensional materials, energy materials, sustainable materials, optoelectronic materials and soft materials. The emphasis will be on rational material design, properties, spectroscopy, modelling and device fabrication.
Low Dimensional Materials 2022
Published in _IISER Pune_, 2024