Spectroscopic Study of the Reversible Chemical Reduction and Reoxidation of Substitutional Cr Ions in Sr<sub>2</sub>TiO<sub>4</sub>

Lehuta, Keith A.; Haldar, Anubhab; Zhou, Dongming; Kittilstved, Kevin R.

doi:10.1021/acs.inorgchem.7b01210

Cited by 5 publications

(3 citation statements)

References 54 publications

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“…28 Previously, some of us demonstrated the introduction of Ti 3+ defects could also be achieved in bulk Cr 3+ -doped SrTiO 3 (and related Sr 2 TiO 4 ) powders using NaBH 4 . 36,37 After this chemical reduction, the Cr 3+ concentration increases by an order of magnitude according to quantitative EPR measurements because of the reduction of EPR-silent Cr species to Cr 3+ prior to formation of Ti 3+ defects. No such increase in the Cr 3+ EPR signal is observed at the start of photodoping (see the Supporting Information).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Reversible Modulation of the Cr³⁺ Spin Dynamics in Colloidal SrTiO₃ Nanocrystals

Harrigan

Kittilstved

2018

J. Phys. Chem. C

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The spin relaxation dynamics of Cr3+ substitutional dopants in ∼10 nm colloidal SrTiO3 nanocrystals (NCs) has been studied by variable-temperature electron paramagnetic resonance (EPR) spectroscopy and continuous wave EPR power saturation measurements between 4.2 and 50 K. The presence of self-trapped electrons introduced by anaerobic ultraviolet irradiation (photodoping) is able to effectively accelerate the spin relaxation dynamics of localized spins of Cr3+ through a cross-relaxation process. The extra electrons introduced during photodoping trap on Ti-sites, creating Ti3+ defects with EPR transitions that are observed only at cryogenic temperatures because of fast spin–lattice relaxation. The change in the spin relaxation upon photodoping the Cr-doped SrTiO3 NCs is totally reversible upon opening the sample to air. This result provides a novel strategy to modulate spin dynamics in individual NCs using photons where long-lived spins on dopant ions couple to the fast-relaxing spins from metastable, transient defects.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Reversible Modulation of the Cr³⁺ Spin Dynamics in Colloidal SrTiO₃ Nanocrystals

Harrigan

Kittilstved

2018

J. Phys. Chem. C

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“…In II–VI semiconductors quantum dots (QDs), incorporation of a dopant metal ion with the same charge (i.e., Mn(II), Cr(II), and Co(II)) leads to simple substitutional incorporation of the ion of interest up to its solubility limit. Incorporation of an ion that has a different charge, such as Cu(I), Cr(III), Eu(III), Fe(III), or Al(III), results in formation of ion vacancies in the QD in order to reach charge neutrality, or in a rare case formation of ZnCr 2 Se 4 spinel inclusion inside Cr(III)-doped ZnSe QDs . The unusual phase segregation in the 2D Mn:CsPbCl 3 NPLs could be understood by the flexible continuum model by considering the effects of coherency strains as well as the gradient energy term in the crystal lattice. , The strain is more significant with high Mn doping concentrations considering the large size mismatch (>30%) between the Mn 2+ (97 pm) dopant and the Pb 2+ (133 pm).…”

Section: Discussionmentioning

confidence: 99%

Complete Dopant Substitution by Spinodal Decomposition in Mn-Doped Two-Dimensional CsPbCl₃ Nanoplatelets

et al. 2018

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The introduction of dopants plays a key role in the physical properties of semiconductors for optoelectronic applications. However, doping is generally challenging for nanocrystals (NCs), especially for two-dimensional (2D) NCs, due to the self-annealing effect and high surface energies required for dopant addition. Here, we report an efficient doping strategy for Mn-doped 2D CsPbCl3 (i.e., Mn:CsPbCl3) nanoplatelets (NPLs) through a postsynthetic solvothermal process. While the original lightly doped 2D Mn:CsPbCl3 NPLs were obtained from growth doping, higher Mn doping efficiencies were achieved through diffusion doping under pressure-mediated solvothermal conditions, resulting in enhanced Mn photoluminescence (PL). Surprisingly, a new CsMnCl3 phase with complete dopant substitution by spinodal decomposition was observed with extended solvothermal treatment, which is confirmed by powder X-ray diffraction, X-ray absorption fine structure, and electron paramagnetic resonance. Compared with Mn:CsPbCl3 NPLs, the pure CsMnCl3 NPLs give rise to shorter Mn PL lifetime, which is consistent with the short Mn–Mn distance within CsMnCl3 NPLs. This work provides an efficient strategy for doping inside NCs as well as new insights on the dopant concentration-dependent structural and optical properties of perovskite NCs.

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“…We previously studied the effect of a relatively low-temperature NaBH 4 reduction reaction on the oxidation state of Cr dopants in SrTiO 3 and related Sr 2 TiO 4 bulk powders (Lehuta and Kittilstved, 2016; Lehuta et al, 2017). In those studies, we observed an order of magnitude increase in the Cr 3+ concentration by EPR spectroscopy that we attributed to the reduction of EPR-silent high-valent Cr 4+ and Cr 6+ ions.…”

Section: Introductionmentioning

confidence: 99%

Reversible Control of the Mn Oxidation State in SrTiO3 Bulk Powders

et al. 2019

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We demonstrate a low-temperature reduction method for exhibiting fine control over the oxidation state of substitutional Mn ions in strontium titanate (SrTiO 3 ) bulk powder. We employ NaBH 4 as the chemical reductant that causes significant changes in the oxidation state and oxygen vacancy complexation with Mn 2+ dopants at temperatures <350°C where lattice reduction is negligible. At higher reduction temperatures, we also observe the formation of Ti 3+ in the lattice by diffuse-reflectance and low-temperature electron paramagnetic resonance (EPR) spectroscopy. In addition to Mn 2+ , Mn 4+ , and the Mn 2+ complex with an oxygen vacancy, we also observe a sharp resonance in the EPR spectrum of heavily reduced Mn-doped SrTiO 3 . This sharp signal is tentatively assigned to surface superoxide ion that is formed by the surface electron transfer reaction between Ti 3+ and O 2 . The ability to control the relative amounts of various paramagnetic defects in SrTiO 3 provides many possibilities to study in a model system the impact of tunable dopant-defect interactions for spin-based electronic applications or visible-light photocatalysis.

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Spectroscopic Study of the Reversible Chemical Reduction and Reoxidation of Substitutional Cr Ions in Sr₂TiO₄

Cited by 5 publications

References 54 publications

Reversible Modulation of the Cr³⁺ Spin Dynamics in Colloidal SrTiO₃ Nanocrystals

Reversible Modulation of the Cr³⁺ Spin Dynamics in Colloidal SrTiO₃ Nanocrystals

Complete Dopant Substitution by Spinodal Decomposition in Mn-Doped Two-Dimensional CsPbCl₃ Nanoplatelets

Reversible Control of the Mn Oxidation State in SrTiO3 Bulk Powders

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Spectroscopic Study of the Reversible Chemical Reduction and Reoxidation of Substitutional Cr Ions in Sr2TiO4

Cited by 5 publications

References 54 publications

Reversible Modulation of the Cr3+ Spin Dynamics in Colloidal SrTiO3 Nanocrystals

Reversible Modulation of the Cr3+ Spin Dynamics in Colloidal SrTiO3 Nanocrystals

Complete Dopant Substitution by Spinodal Decomposition in Mn-Doped Two-Dimensional CsPbCl3 Nanoplatelets

Reversible Control of the Mn Oxidation State in SrTiO3 Bulk Powders

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Spectroscopic Study of the Reversible Chemical Reduction and Reoxidation of Substitutional Cr Ions in Sr₂TiO₄

Reversible Modulation of the Cr³⁺ Spin Dynamics in Colloidal SrTiO₃ Nanocrystals

Reversible Modulation of the Cr³⁺ Spin Dynamics in Colloidal SrTiO₃ Nanocrystals

Complete Dopant Substitution by Spinodal Decomposition in Mn-Doped Two-Dimensional CsPbCl₃ Nanoplatelets