Browsing by Author "Modanwal S."

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    Multimodal spectral emissions in Tb3+/Yb3+ ions doped/co-doped self-activated LaNbO4 phosphor: Applications as 3D imaging for security and solar cells
    (Elsevier Ltd, 2024) Modanwal S.; Roy A.; Mishra H.; Rai S.B.
    The present work reports the multimodal spectral emissions through downshifting [DS], quantum cutting [QC], and up-conversion [UC] processes in a newly synthesized Tb3+ and Yb3+ ions doped/ co-doped self-activated LaNbO4 phosphor by solid-state reaction method at 1473 K. The synthesized phosphor material's structural, optical, and photo-physical characterizations have been made by XRD, SEM, XPS, FTIR, UV/Visible/NIR absorption, emission, and time domain luminescence measurements. XRD and SEM characterizations of LaNbO4:Tb3+,Yb3+ show a monoclinic phase with average micron range particle size, respectively. LaNbO4 shows a strong charge transfer [CTB] band at 262 nm and corresponding intense emission at 418 nm with a decay time of 4.33 ?s. In the presence of different concentrations of Tb3+ ions, LaNbO4 phosphor samples show blue to green color-tunable DS emissions due to 5D3,4?7FJ transitions of Tb3+ ion with 262 nm (UV) and 378 nm (n-UV) excitations and found intense green emission with optimum for 15 mol% Tb3+. The multipolar interaction has been found responsible for excitation energy transfer from the host to Tb3+ ions. Further, in the presence of different concentrations of Yb3+ ion, La0.85NbO4:0.15Tb3+ phosphor shows UC emission in blue, green, orange, and red regions corresponding to 5D4?7FJ transitions of Tb3+ ion by NIR [980 nm] excitation. Alongwith UC, LaNbO4:Tb3+, Yb3+ phosphor converts strongly the UV, and visible photons into two NIR photons via quantum cutting (QC) process. In time domain measurements, a decrease in the decay time of the host in the presence of Tb3+ ions and the appearance of rise time in the decay measurements of 5D4 ?7FJ transitions of Tb3+ ion support the electronic excitation energy transfer from the host to Tb3+ ion is DS process on 262 nm excitation. The intense green emission obtained from this phosphor under UV/Vis/NIR excitation makes this system attractive for security markers/signaling by producing 3D images/display devices and the intense NIR emission which can be utilized to enhance the efficiency of c-Si solar cells. � 2024 Elsevier B.V.
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    Upconversion, downshifting, quantum cutting and back energy trasfer from Yb3+ to Er3+ in Er3+/Yb3+ co-doped CaTiO3 phosphor, intense NIR generation for communication
    (Elsevier Ltd, 2024) Singh P.; Modanwal S.; Mishra H.; Rai S.B.
    The perovskite based phosphor materials are widely used to increase the efficiency of solar cells. In this work, Er3+ doped and Er3+/Yb3+ co-doped CaTiO3 perovskite phosphor samples have been synthesized by solid state reaction technique at 1473 K. The phosphor samples show orthorhombic phase with Pnma (62) space group. The average crystallites and particles size of CaTiO3 are increased in presence of Er3+ and Yb3+ ions. Er3+ doped CaTiO3 phosphor samples give downshifting emission under 379 nm excitation. Though upconversion emission is seen in Er3+ under 980 nm excitation without Yb3+ ions in this host. The emission intensity of Er3+ ion is enhanced by 46 and 16 times for green and red emissions, respectively in presence of Yb3+. An intense quantum cutting (QC) emission is observed at 980 nm in presence of Yb3+ in CaTiO3:0.5Er3+ phosphor under 379 nm excitation. The QC efficiency has been found to be 119 % for CaTiO3:0.5Er3+/5 Yb3+ phosphor. Further an interesting phenomenon of back energy transfer (BEnT) from Yb3+ to Er3+ giving an intense NIR emission from Er3+ at 1002 and 1550 nm have been observed. The phosphor sample also shows an intrinsic optical bistablity (IOB) by upconversion. Thus, the prepared phosphor samples may be useful to increase the efficiency of c-Si solar cell, NIR emission for communication, bistable material and green light emitting source. � 2024 Elsevier Ltd and Techna Group S.r.l.