Characteristic features of the nanocrystalline structure formation in Ln2Hf2O7 (Ln = Gd, Dy) compounds

Попов, В. В.; Менушенков, А. П.; Zubavichus, Ya. V.; Yaroslavtsev, Alexander; Leshchev, Denis; Kulik, Eleonora; Bednarčı́k, J.; Петрунин, В. Ф.; Korovin, S. A.; Chernikov, Roman

doi:10.1134/s0036023613120164

Cited by 19 publications

(6 citation statements)

References 21 publications

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“…In another work, Popov et al. have also observed the formation of the OP structure from GHO NPs at 1200–1300 °C. − However, our XRD results do not reveal the OP phase even from the GHOE-1300 NPs. Because of the closeness of the atomic numbers of gadolinium ( Z = 64) and hafnium ( Z = 72), the superstructure reflections are too small to be observed by nonresonant diffraction studies to confirm the formation of the long-range cationic order of the pyrochlore phase …”

Section: Results and Discussioncontrasting

confidence: 67%

“…13 numbers of gadolinium (Z = 64) and hafnium (Z = 72), the superstructure reflections are too small to be observed by nonresonant diffraction studies to confirm the formation of the long-range cationic order of the pyrochlore phase. 38 As can be seen from Table 1, there is a proportional increase in crystalline size of the GHOE NPs as a function of annealing temperature. This can also be seen from the narrowing of the XRD peaks at a higher annealing temperature.…”

Section: Resultsmentioning

confidence: 87%

“…Because of the closeness of the atomic numbers of gadolinium ( Z = 64) and hafnium ( Z = 72), the superstructure reflections are too small to be observed by nonresonant diffraction studies to confirm the formation of the long-range cationic order of the pyrochlore phase. 38…”

Section: Results and Discussionmentioning

confidence: 99%

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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: Results and Discussioncontrasting

confidence: 67%

Section: Resultsmentioning

confidence: 87%

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

et al. 2019

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“…In recent years we actively investigated the structure formation in boundary compounds: Gd 2 Zr 2 O 7 with γ = 1.46 [41] and Ln 2 Hf 2 O 7 (Ln = Sm-Dy) with γ = 1.45 − 1.51 [42][43][44][45]. The present work addresses the specific features of lanthanide hafnates 110 Ln 2 Hf 2 O 7 crystal and local structures during their emergence and evolution.…”

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confidence: 99%

Fluorite-pyrochlore phase transition in nanostructured Ln2Hf2O7 (Ln = La-Lu)

Попов

Менушенков

Yaroslavtsev

et al. 2016

Journal of Alloys and Compounds

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“…The REE hafnates Ln 2 + х M 2 -х O 7 -х/2 have higher melting points and temperatures of the pyrochlore-fluorite phase transi tion as compared to the analogous zirconates Ln 2 Hf 2 O 7 [4,6]. Most interesting from a scientific point of view are the compounds with the ratio of the cation radii ~ 1.46, which can have both pyrochlore and fluorite structures [5,7]; and also the hafnates formed by Er and other (smaller in size) REE r Ln 3+ /r Hf 4+ cations, in which the formation of δ phases is possible due to the fluorite → δ phase transition [5].…”

mentioning

confidence: 99%

Studying processes of crystallization and cation ordering in Eu2Hf2O7

Попов

Менушенков

Zubavichus

et al. 2015

Russ. J. Inorg. Chem.

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Methods of local X ray anomalous diffraction and X ray absorption spectroscopy based on the interaction of synchrotron radiation with condensed matter have been used to study the processes of forma tion and evolution of the crystal structure in Eu 2 Hf 2 O 7 powders. It has been shown that the isothermal anneal ing of the X ray amorphous mixed hydroxide leads initially to the formation of nanocrystalline powders, which have a defect fluorite structure with a clearly pronounced nonequivalence of the local environment of the Eu 3+ and Hf 4+ cations. An increase in the temperature of heat treatment to ≥1200°C leads to the nucle ation and growth of nanodomains with a superstructural cation ordering of the pyrochlore type inside the coarse crystallites of the defect fluorite and, finally, at T ≥ 1500°C, to the complete phase transition of the flu orite-pyrochlore type in the Eu 2 Hf 2 O 7 system. In the pyrochlore Eu 2 Hf 2 O 7 structure, there was for the first time revealed a simultaneous broadening of the shape of the L 3 absorption edges of both hafnium and europium, which indicates a partial change in the symmetry of the nearest oxygen environment of both cations.

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Characteristic features of the nanocrystalline structure formation in Ln2Hf2O7 (Ln = Gd, Dy) compounds

Cited by 19 publications

References 21 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

Fluorite-pyrochlore phase transition in nanostructured Ln2Hf2O7 (Ln = La-Lu)

Studying processes of crystallization and cation ordering in Eu2Hf2O7

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Characteristic features of the nanocrystalline structure formation in Ln2Hf2O7 (Ln = Gd, Dy) compounds

Cited by 19 publications

References 21 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

Fluorite-pyrochlore phase transition in nanostructured Ln2Hf2O7 (Ln = La-Lu)

Studying processes of crystallization and cation ordering in Eu2Hf2O7

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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