Speciation of uranium and doping induced defects in Gd1.98U0.02Zr2O7: Photoluminescence, X-ray photoelectron and positron annihilation lifetime spectroscopy

Gupta, Santosh K.; Reghukumar, C.; Pathak, Nimai; Sudarshan, K.; Tyagi, Deepak; Mohapatra, M.; Pujari, P. K.; Kadam, R.M.

doi:10.1016/j.cplett.2016.11.005

Cited by 29 publications

(19 citation statements)

References 55 publications

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“…Materials with A 2 B 2 O 7 composition belonging to the pyrochlore group have been the focal point of research in the scientific community for the past few decades owing to their various interesting properties such as low thermal conductivity, high dielectric constant, suitable refractive index, high structural stability, high radiation stability, and so forth. These properties enable them to be suitable for many applications such as catalysis, phosphor, nuclear waste host, scintillator, , defect fluorescence, magnetism, thermal barrier coatings, and sensors . They are known to exist in two structural variants: ordered pyrochlore (OP, Fd 3̅ m ) and disordered fluorite (DF, Fm 3̅ m ).…”

Section: Introductionmentioning

confidence: 99%

Thermally Induced Disorder–Order Phase Transition of Gd₂Hf₂O₇:Eu³⁺ Nanoparticles and Its Implication on Photo- and Radioluminescence

et al. 2019

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Crystal structure has a strong influence on the luminescence properties of lanthanide-doped materials. In this work, we have investigated the thermally induced structural transition in Gd 2 Hf 2 O 7 (GHO) using Eu 3+ ions as the spectroscopic probe. It was found that complete phase transition from the disordered fluorite phase (DFP) to the ordered pyrochlore phase (OPP) can be achieved in GHO with the increase of annealing temperature from 650 → 1100 → 1300 °C. OPP is the more stable structural form for the GHOE nanoparticles (NPs) annealed at a higher temperature based on the energy calculation by density functional theory (DFT). The asymmetry ratio of the GHOE-650 NPs was the highest, whereas the quantum yield, luminescence intensity, and lifetime values of the GHOE-1300 NPs were the highest. Emission intensity of Eu 3+ ions increases significantly with the phase transition from the DFP to OPP phase and is attributed to the higher radiative transition rate (281 s –1 ) of the 5 D 0 level of the Eu 3+ ion in the environment with relatively lower symmetry ( C 2 v ) because of the increase of crystal size. As the structure changes from DFP to OPP, radioluminescence showed tunable color change from red to orange. The Eu 3+ local structure obtained from DFT calculation confirmed the absence of inversion symmetry in the DFP structure, which is consistent with the experimental emission spectra and Stark components. We also elucidated the host to dopant optical energy transfer through density of states calculations. Overall, our current studies present important observations for the GHOE NPs: (i) thermally induced order–disorder phase transition, (ii) change of point group symmetry around Eu 3+ ions in the two phases, (iii) high thermal stability, and (iv) tunability of radioluminescent color. This work provides fundamental understanding of the relationship between the crystal structure and photophysical properties of lanthanide-doped materials and helps design a strategy for advanced optoelectronic materials.

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Section: Introductionmentioning

confidence: 99%

Thermally Induced Disorder–Order Phase Transition of Gd₂Hf₂O₇:Eu³⁺ Nanoparticles and Its Implication on Photo- and Radioluminescence

et al. 2019

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“…The uranyl ion can be stabilized in +3, +4, +5, and also +6 oxidation states. Many researchers have conducted the stabilization of various oxidation states and PL study of uranyl species. − …”

Section: Resultsmentioning

confidence: 99%

Enrichment of Crystal Field Modification via Incorporation of Alkali K⁺ Ions in YVO₄:Ho³⁺/Yb³⁺ Nanophosphor and Its Hybrid with Superparamagnetic Iron Oxide Nanoparticles for Optical, Advanced Anticounterfeiting, Uranyl Detection, and Hyperthermia Applications

et al. 2021

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In this work, we report a polyol route for easy synthesis of upconversion (UC) phosphor nanoparticles, YVO 4 :Ho 3+ -Yb 3+ -K + , which enables large-scale production and enhancement of luminescence. Upon 980 nm laser excitation, the UC emission spectrum shows a sharp bright peak at ∼650 nm of Ho 3+ ion; and the luminescence intensity increases twofold upon K + codoping. Upon 300 nm excitation, the downconversion emission spectrum shows a broad peak in the 400−500 nm range (related to the charge transfer band of V−O) along with Ho 3+ peaks. In addition, the polyethylene glycolcoated UC nanoparticles are highly water-dispersible and their hybrid with Fe 3 O 4 nanoparticles shows magnetic-luminescence properties. A hyperthermia temperature is achieved from this hybrid. Both UC and hybrid nanoparticles show interesting security ink properties upon excitation by a 980 nm laser. The particles are invisible in normal light but visible upon 980 nm excitation and are useful in display devices, advanced anticounterfeiting purposes, and therapy of cancer via hyperthermia and bioimaging (since it shows red emission at ∼650 nm). Using UC nanoparticles, detection of uranyl down to 20 ppm has been achieved.

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“…HLW, such as uranium (U) and its isotopes, needs to be properly disposed of at high concentrations due to its presence in large quantities in spent fuel, even after reprocessing . Due to the multiple oxidation states and their respective health hazards, these compounds need to be carefully contained in the proper host matrix .…”

Section: Introductionmentioning

confidence: 99%

“…Depending on the synthesis conditions, thermal treatment, and the host matrix, U 6+ can form UO 4 2– , UO 6 6– , and UO 2 2+ in different molecular structures. Of these uranium ions, UO 2 2+ is the most stable and established form of natural and spent uranium in the environment . There is a large body of literature on studying the U oxidation states in pyrochlore nanoparticles such as Gd 2 Zr 2 O 7 , Nd 2 Zr 2 O 7 , and La 2 Zr 2 O 7 . − However, the effect of high U doping concentration to the local structure, as well as the formation of different U compounds in different host matrices, has not been investigated systematically for the formation of highly stable HLW materials.…”

Section: Introductionmentioning

confidence: 99%

“…22 HLW, such as uranium (U) and its isotopes, needs to be properly disposed of at high concentrations due to its presence in large quantities in spent fuel, even after reprocessing. 23 Due to the multiple oxidation states and their respective health hazards, these compounds need to be carefully contained in the proper host matrix. 24 Depending on the synthesis conditions, thermal treatment, and the host matrix, U 6+ can form UO 4 2− , UO 6 6− , and UO 2 2+ in different molecular structures.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Oxide Ion Distribution on a Uranium Structure in Highly U-Doped RE₂Hf₂O₇ (RE = La and Gd) Nanoparticles

et al. 2020

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Rare-earth based A 2 B 2 O 7 compounds have been considered as potential host materials for nuclear waste due to their exceptional chemical, physical, capability of accommodating high concentration of actinides at both A-and B-sites, negligible leaching, tendency to form antisite defects, and radiation stabilities. In this work, La 2 Hf 2 O 7 (LHO) and Gd 2 Hf 2 O 7 (GHO) nanoparticles (NPs) were chosen as the RE-based hafnates to study the structural changes and the formation of different U molecular structures upon doping (or alloying) at high concentration (up to 30 mol %) using a combined coprecipitation and molten-salt synthesis. These compounds form similar crystal structures, i.e., ordered pyrochlore (LHO) and disordered fluorite (GHO), but are expected to show different phase transformations at high U doping concentration. X-ray diffraction (XRD) and Rietveld refinement results show that the LHO:U NPs have high structural stability, whereas the GHO:U NPs exhibit a highly disordered structure at high U concentration. Alternatively, the vibrational spectra show an increasingly random oxygen distribution with U doping, driving the LHO:U NPs to the disordered fluorite phase. X-ray spectroscopy indicates that U is stabilized as different U 6+ species in both LHO and GHO hosts, resulting in the formation of oxygen vacancies stemming from the U local coordination and different phase transformation. Interestingly, the disordered fluorite phase has been reported to have increased radiation tolerance, suggesting multiple benefits associated with the LHO host. These results demonstrate the importance of the structural and chemical effect of actinide dopants on similar host matrices which are important for the development of REbased hafnates for nuclear waste hosts, sensors, thermal barrier coatings, and scintillator applications.

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Speciation of uranium and doping induced defects in Gd1.98U0.02Zr2O7: Photoluminescence, X-ray photoelectron and positron annihilation lifetime spectroscopy

Cited by 29 publications

References 55 publications

Thermally Induced Disorder–Order Phase Transition of Gd₂Hf₂O₇:Eu³⁺ Nanoparticles and Its Implication on Photo- and Radioluminescence

Thermally Induced Disorder–Order Phase Transition of Gd₂Hf₂O₇:Eu³⁺ Nanoparticles and Its Implication on Photo- and Radioluminescence

Enrichment of Crystal Field Modification via Incorporation of Alkali K⁺ Ions in YVO₄:Ho³⁺/Yb³⁺ Nanophosphor and Its Hybrid with Superparamagnetic Iron Oxide Nanoparticles for Optical, Advanced Anticounterfeiting, Uranyl Detection, and Hyperthermia Applications

Effect of Oxide Ion Distribution on a Uranium Structure in Highly U-Doped RE₂Hf₂O₇ (RE = La and Gd) Nanoparticles

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Speciation of uranium and doping induced defects in Gd1.98U0.02Zr2O7: Photoluminescence, X-ray photoelectron and positron annihilation lifetime spectroscopy

Cited by 29 publications

References 55 publications

Thermally Induced Disorder–Order Phase Transition of Gd2Hf2O7:Eu3+ Nanoparticles and Its Implication on Photo- and Radioluminescence

Thermally Induced Disorder–Order Phase Transition of Gd2Hf2O7:Eu3+ Nanoparticles and Its Implication on Photo- and Radioluminescence

Enrichment of Crystal Field Modification via Incorporation of Alkali K+ Ions in YVO4:Ho3+/Yb3+ Nanophosphor and Its Hybrid with Superparamagnetic Iron Oxide Nanoparticles for Optical, Advanced Anticounterfeiting, Uranyl Detection, and Hyperthermia Applications

Effect of Oxide Ion Distribution on a Uranium Structure in Highly U-Doped RE2Hf2O7 (RE = La and Gd) Nanoparticles

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Thermally Induced Disorder–Order Phase Transition of Gd₂Hf₂O₇:Eu³⁺ Nanoparticles and Its Implication on Photo- and Radioluminescence

Thermally Induced Disorder–Order Phase Transition of Gd₂Hf₂O₇:Eu³⁺ Nanoparticles and Its Implication on Photo- and Radioluminescence

Enrichment of Crystal Field Modification via Incorporation of Alkali K⁺ Ions in YVO₄:Ho³⁺/Yb³⁺ Nanophosphor and Its Hybrid with Superparamagnetic Iron Oxide Nanoparticles for Optical, Advanced Anticounterfeiting, Uranyl Detection, and Hyperthermia Applications

Effect of Oxide Ion Distribution on a Uranium Structure in Highly U-Doped RE₂Hf₂O₇ (RE = La and Gd) Nanoparticles