Browsing by Author "Ankur Shandilya"

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Effects of Yb3+ ion doping on lattice distortion, optical absorption and light upconversion in Er3+/Yb3+ co-doped SrMoO4 ceramics
(Elsevier Ltd, 2021) Ankur Shandilya; Ram Sagar Yadav; Ajai K. Gupta; K. Sreenivas
Sintered ceramic pellets of rare-earth ion doped strontium molybdate compositions Sr1-x-yErxYbyMoO4 (x = 1 mol%; y = 0–9 mol%) were prepared using solid-state reaction method. Rietveld refinement of HR-XRD data reveals a high degree of lattice distortion for y = 3 mol %, and correspondingly a maximum deviation in the O–Sr–O and Mo–O bonds. Raman spectroscopy indicates the substitution of Er3+ and Yb3+ at the SrO8 polyhedron clusters of the SrMoO4 unit cell, and infrared absorption shows changes in the molybdenum-oxygen (Mo–O) bond strength in the [MoO4]2⎻ cluster. Variations in the optical band gap are attributed to positional change of oxygen octahedra and local bond distortion in the unit cell. A selective enhancement in green up-conversion luminescence is seen at y = 3 mol %, and originates due to direct contribution from the [Yb3+⎼MoO4]2- dimer complex sensitization, and correlates with the presence of high lattice distortion. A progressive increase in lifetime of the 4S3/2 from 0.195 to 0.424 ms at y = 0.03 increase the radiative transition probability and UC emission. Luminescence quenching for Yb3+ ion content (y > 0.03) is due to the reduced asymmetrical arrangement around erbium ion and corresponding changes in the Sr–O and Mo–O bond lengths. These studies provide new insight into the quenching effect and formulate a new strategy to design ceramic compositions for better UC performance. © 2021 Elsevier B.V.
Temperature-dependent light upconversion and thermometric properties of Er3+/Yb3+-codoped SrMoO4 sintered ceramics
(Springer, 2021) Ankur Shandilya; Ram Sagar Yadav; Ajai K. Gupta; K. Sreenivas
A series of Sr1−x−yErxYbyMoO4 phosphor compositions codoped with Er3+ (x = 1 mol%) and varying Yb3+ (y = 0–9 mol%) dopants have been evaluated for luminescence-based thermometry. Sintered ceramics exhibit enhanced grain growth at an optimum Yb3+ content (y = 0.03) and exhibit improved upconversion luminescence and a relatively better thermometric performance over the phosphors in the powder form. Strong upconversion (UC) luminescence at ~ 529, ~ 552, and ~ 662 nm assisted by a 2-photon process, cooperative luminescence from Yb3+ ion pair at 495 nm, and weak UC emissions at ~ 380 and ~ 410 nm due to 3-photon process are identified. Luminescence quenching is observed in all the UC emission bands for Yb3+ content y > 3 mol%. Sensitization from Yb3+ to Er3+ and Yb3+–(MoO4)2− dimer to Er3+ ions results in selective enhancement of the green emission. Variation of UC emission intensity with increasing dopant concentration is analyzed using Dexter’s energy transfer formula, which supports the dipole–dipole interaction between Yb3+ and Er3+ ions. Changes in fluorescence intensity ratio (I529/I552) with temperature reveal the potential usefulness of the optimized Sr0.96Er0.01Yb0.03MoO4 phosphor composition in the ceramic form for non-contact optical thermometry and exhibits good repeatability for temperature sensing applications. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.