Browsing by Author "Santosh Kachhap"

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Effect of Mn2+ doping and DDAB-assisted postpassivation on the structural and optical properties of CsPb(Cl/Br)3 halide perovskite nanocrystals
(Institute of Physics, 2024) Charu Dubey; Anjana Yadav; Santosh Kachhap; Sunil Kumar Singh; Govind Gupta; Satendra Pal Singh; Akhilesh Kumar Singh
Cesium lead halide perovskite (CsPbX3; X = Cl, Br, I) nanocrystals showing intense band-edge emission and high photoluminescence quantum yield are known to be a potential candidate for application in optoelectronic devices. However, controlling toxicity due to the presence of Pb2+ in lead-based halide perovskites is a major challenge for the environment that needs to be tackled cautiously. In this work, we have partially replaced Pb2+ with Mn2+ ions in the CsPb(Cl/Br)3 nanocrystals and investigated their impact on the structural and optical properties. The Rietveld refinement shows that CsPbCl2Br nanocrystals possess a cubic crystal structure with Pm 3 ̅ m space group, the Mn2+ doping results in the contraction of the unit cell. The CsPb(Cl/Br)3: Mn nanocrystals show a substantial change in the optical properties with an additional emission band at ∼588 nm through a d-d transition, changing the emission color from blue to pink. Here, a didodecyldimethylammonium bromide (DDAB) ligand that triggers both anion and ligand exchange in the CsPb(Cl/Br)3: Mn nanocrystals have been used to regulate the exchange reaction and tune the emission color of halide perovskites by changing the peak position and the PL intensities of band-edge and Mn2+ defect states. We have also shown that oleic acid helps in the desorption of oleylamine capping from the CsPb(Cl/Br)3: Mn nanocrystal surfaces and DDAB, resulting in the substitution of Cl− with Br− as well as provides capping with shorter branched length ligand which led to increase in the overall PL intensity by many folds. © 2024 IOP Publishing Ltd.
Temperature sensing using bulk and nanoparticles of Ca0.79Er0.01Yb0.2MoO4phosphor
(Institute of Physics, 2022) Sachin Singh; Santosh Kachhap; Akhilesh Kumar Singh; Sasank Pattnaik; Sunil Kumar Singh
Optical temperature sensing is widely realized by using upconversion (UC) emission in lanthanide-doped phosphors. There are various parameters that are responsible for UC intensity of the phosphor like particle shape and size, type of symmetry that exist at the site position, distribution of lanthanide ions in the phosphor, and so on. However, a comparative study of the bulk and nanostructure on the temperature sensing ability of such phosphor is rare. In the present work, we have taken Ca0.79Er0.01Yb0.2MoO4 phosphors as a model system and synthesized its bulk (via solid-state reaction method, named SCEY) and nanostructures (via solution combustion route, named CCEY). We further studied their phase, crystal structure, phonon frequency, optical excitation, and emission (upconversion & downshifting) properties. Finally, the optical temperature sensing behavior of SCEY and CCEY, in the range 305 K-573 K, have been compared. The maximum relative sensitivity of the phosphor SCEY and CCEY are 0.0061 K-1 at 305 K and 0.0094 K-1 at 299 K, respectively, while, the maximum absolute sensitivities are 0.0150 K-1 at 348 K, and 0.0170 K-1 at 398 K, respectively. We thus conclude that the temperature sensing ability of nanoparticle-based Ca0.79Er0.01Yb0.2MoO4 phosphor is better compared to its bulk phosphor. © 2022 IOP Publishing Ltd.