Deciphering the Role of Charge Compensator in Optical Properties of SrWO4:Eu3+:A (A = Li+, Na+, K+): Spectroscopic Insight Using Photoluminescence, Positron Annihilation, and X-ray Absorption

Gupta, Santosh K.; Sudarshan, K.; Yadav, Ashok K.; Gupta, Ruma; Bhattacharyya, D.; Jha, S. N.; Kadam, R.M.

doi:10.1021/acs.inorgchem.7b02780

Cited by 94 publications

(29 citation statements)

References 60 publications

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“…For all doped inorganic substances, the concentration of the dopants has a critical influence on their lattice parameters. As previously reported, , a solid-state reaction can ensure the dopant content in the scheelite lattice. Different from the bulk substances prepared by the solid-state reaction, the concentration of dopants in the studied substances prepared by the solution’s chemical route could deviate from the initially expected values, because of the different behaviors of the dopants and host ions in the reaction solution .…”

Section: Results and Discussionsupporting

confidence: 55%

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO₄ by Hydrothermal Conditions

Gao

Geng

et al. 2021

Inorg. Chem.

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Doping chemistry has become one of the most effective means of tuning materials' properties for diverse applications. In particular for scheelite-type CaWO 4 , highoxidation-state doping is extremely important, since one may expand the scheelite family and further create prospective candidates for novel applications and/or useful spectral signatures for nuclear forensics. However, the chemistry associated with highvalence doping in scheelite-type CaWO 4 is far from understanding. In this work, a series of scheelite-based materials (Ca 1−x−y−z Eu x K y □ z )WO 4 (□ represents the cation vacancy of the Ca 2+ site) were synthesized by hydrothermal conditions and solid-state methods and comparatively studied. For the bulk prepared by the solid-state method, occupation of high-oxidation-state Eu 3+ at the Ca 2+ sites of CaWO 4 is followed by doping of the low-oxidation-state K + at a nearly equivalent molar amount. The Eu 3+ local symmetry is thus varied from the original S 4 point group symmetry to C 2v point group symmetry. Surprisingly different from the cases in bulk, for the nanoscale counterparts prepared by hydrothermal conditions, the high-oxidation-state Eu 3+ was incorporated in CaWO 4 at two distinct sites, and its amount is higher than that of the low-oxidation-state K + even though KOH was used as a mineralizer, creating a certain amount of cation vacancies. Consequently, an apparent split emission of 5 D 0 → 7 F 0 was first demonstrated for (Ca 1−x−y−z Eu x K y □ z )WO 4 . The doping chemistry of high oxidation states uncovered in this work not only provides an explanation for the commonly observed spectral changes in rare-earth-ion-modified scheelite structures, but also points out an advanced direction that can guide the design and synthesis of novel functional oxides by solution chemistry routes.

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Section: Results and Discussionsupporting

confidence: 55%

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO₄ by Hydrothermal Conditions

Gao

Geng

et al. 2021

Inorg. Chem.

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“…The emission peak positioned at around 653 nm is ascribed to 5 D 0 → 7 F 3 , which is not allowed by either MDT or EDT, and the peak at 710 nm due to 5 D 0 → 7 F 4 is allowed by EDT. The very high intensity of hypersensitive EDT compared to MDT clearly suggests that a very large fraction of europium is localized in a site with low symmetry. , This is also evident from the large extent of spectral splitting in all of the peaks. The number of Stark peaks in hypersensitive EDT and MDT, which are 5 and 3, suggests that the point group symmetry of the europium ion in CSOE is C2 .…”

Section: Resultsmentioning

confidence: 96%

Achieving Bright Blue and Red Luminescence in Ca₂SnO₄ through Defect and Doping Manipulation

et al. 2020

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Designing a bright blue and red phosphor for phosphor-converted whitelight-emitting diodes would be extremely beneficial to the lighting industry. Achieving the same through defect and doping engineering in an interesting inorganic layered structure material, Ca 2 SnO 4 (CSO), would fetch a lot of interest among material and optical scientists. There is no report on undoped and doped CSO lattices where extensive effort has been made to understand the origin of host emission, local site occupancy, defect evolution, etc. With the same intention, in this work, we have investigated the photophysical properties of undoped and Eu 3+ -doped CSO (CSOE). On UV irradiation, CSO displayed beautiful blue emission, and its origin has been explained experimentally using extended X-ray absorption fine structure (EXAFS) and theoretically using density functional theory (DFT) calculations. Both DFT and EXFAS pinpointed the role of oxygen vacancies (OVs) in blue emission of CSO. In fact, by extensive calculations, we also found out that both neutral and charged oxygen vacancies are involved in producing blue emission in CSO. To further tune the luminescence, the Eu 3+ ion was doped in CSO, which produces highly pure red emission with an internal quantum efficiency (IQE) of ∼80% and negligible nonradiative transition. Based on EXAFS and lifetime spectroscopy, it was found that the Eu 3+ ion is localized in a much higher fraction at the CaO 7 site compared to SnO 6 octahedra. This was further substantiated using DFT-calculated formation energies. Further, it is expected that aliovalent doping of the trivalent Eu 3+ ion at Ca 2+ /Sn 4+ leads to charge-compensating defects, which significantly impact the optical properties of CSOE, and were further investigated using positron annihilation lifetime spectroscopy (PALS). Such complete spectrum of work wherein photophysical properties of functional materials are optimized and studied by deciphering the role of OVs, local site occupancy of the dopant ion, and charge-compensating defects will inculcate a lot of interest within the scientific community in coming forward for research in the area of rare-earth-free phosphor as well as doped phosphor for solving the energy crisis.

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“…This is an additional advantage of our LHOS NPs because such defects as nonradiative pathways are deleterious and adversely affect their performance. 55…”

Section: Resultsmentioning

confidence: 99%

Samarium-Activated La₂Hf₂O₇ Nanoparticles as Multifunctional Phosphors

et al. 2019

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Recent developments in the field of designing novel nanostructures with various functionalities have pushed the scientific world to design and develop high-quality nanomaterials with multifunctional applications. Here, we propose a new kind of doped metal oxide pyrochlore nanostructure for solid-state phosphor, X-ray scintillator, and optical thermometry. The developed samarium-activated La2Hf2O7 (LHOS) nanoparticles (NPs) emit a narrow and stable red emission with lower color temperature and adequate critical distance under near-UV and X-ray excitations. When the LHOS NPs are exposed to an energetic X-ray beam, the Sm3+ ions situated at the symmetric environment get excited along with those located at the asymmetric environment, which results in a low asymmetry ratio of Sm3+ under radioluminescence compared to photoluminescence. High activation energy and adequate thermal sensitivity of the LHOS NPs highlight their potential as a thermal sensor. Our results indicate that these Sm3+-activated La2Hf2O7 NPs can serve as a multifunctional UV, X-ray, and thermographic phosphor.

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Deciphering the Role of Charge Compensator in Optical Properties of SrWO₄:Eu³⁺:A (A = Li⁺, Na⁺, K⁺): Spectroscopic Insight Using Photoluminescence, Positron Annihilation, and X-ray Absorption

Cited by 94 publications

References 60 publications

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO₄ by Hydrothermal Conditions

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO₄ by Hydrothermal Conditions

Achieving Bright Blue and Red Luminescence in Ca₂SnO₄ through Defect and Doping Manipulation

Samarium-Activated La₂Hf₂O₇ Nanoparticles as Multifunctional Phosphors

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Deciphering the Role of Charge Compensator in Optical Properties of SrWO4:Eu3+:A (A = Li+, Na+, K+): Spectroscopic Insight Using Photoluminescence, Positron Annihilation, and X-ray Absorption

Cited by 94 publications

References 60 publications

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO4 by Hydrothermal Conditions

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO4 by Hydrothermal Conditions

Achieving Bright Blue and Red Luminescence in Ca2SnO4 through Defect and Doping Manipulation

Samarium-Activated La2Hf2O7 Nanoparticles as Multifunctional Phosphors

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Deciphering the Role of Charge Compensator in Optical Properties of SrWO₄:Eu³⁺:A (A = Li⁺, Na⁺, K⁺): Spectroscopic Insight Using Photoluminescence, Positron Annihilation, and X-ray Absorption

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO₄ by Hydrothermal Conditions

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO₄ by Hydrothermal Conditions

Achieving Bright Blue and Red Luminescence in Ca₂SnO₄ through Defect and Doping Manipulation

Samarium-Activated La₂Hf₂O₇ Nanoparticles as Multifunctional Phosphors