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Charge transfer induced energy storage in CaZnOS:Mn : insight from experimental and computational spectroscopy

Jonas Joos (UGent) , Kurt Lejaeghere (UGent) , Katleen Korthout (UGent) , Ang Feng (UGent) , Dirk Poelman (UGent) and Philippe Smet (UGent)
(2017) PHYSICAL CHEMISTRY CHEMICAL PHYSICS. 19(13). p.9075-9085
Author
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Center for nano- and biophotonics (NB-Photonics)
Abstract
CaZnOS: Mn2+ is a rare-earth-free luminescent compound with an orange broadband emission at 612 nm, featuring pressure sensing capabilities, often explained by defect levels where energy can be stored. Despite recent efforts from experimental and theoretical points of view, the underlying luminescence mechanisms in this phosphor still lack a profound understanding. By the evaluation of thermoluminescence as a function of the charging wavelength, we probe the defect levels allowing energy storage. Multiple trap depths and trapping routes are found, suggesting predominantly local trapping close to Mn2+ impurities. We demonstrate that this phosphor shows mechanoluminescence which is unexpectedly stable at high temperature (up to 200 degrees C), allowing pressure sensing in a wide temperature range. Next, we correlate the spectroscopic results with a theoretical study of the electronic structure and stability of the Mn defects in CaZnOS. DFT calculations at the PBE+U level indicate that Mn impurities are incorporated on the Zn site in a divalent charge state, which is confirmed by X-ray absorption spectroscopy (XAS). Ligand-to-metal charge transfer (LMCT) is predicted from the location of the Mn impurity levels, obtained from the calculated defect formation energies. This LMCT proves to be a very efficient pathway for energy storage. The excited state landscape of the Mn2+ 3d(5) electron configuration is assessed through the spin-correlated crystal field and a good correspondence with the emission and excitation spectra is found. In conclusion, studying phosphors at both a singleparticle level (i.e. via calculation of defect formation energies) and a many-particle level (i.e. by accurately localizing the excited states) is necessary to obtain a complete picture of luminescent defects, as demonstrated in the case of CaZnOS: Mn2+.
Keywords
luminescence, mechanoluminescence, manganese, crystal field theory, DFT, modeling, charge transfer, DENSITY-FUNCTIONAL THEORY, RARE-EARTH IONS, VIBRONIC SPECTRA, AB-INITIO, LUMINESCENCE PROPERTIES, ALKALI-HALIDES, LIGAND-FIELD, PHOSPHORS, 1ST-PRINCIPLES, LANTHANIDE

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Chicago
Joos, Jonas, Kurt Lejaeghere, Katleen Korthout, Ang Feng, Dirk Poelman, and Philippe Smet. 2017. “Charge Transfer Induced Energy Storage in CaZnOS:Mn : Insight from Experimental and Computational Spectroscopy.” Physical Chemistry Chemical Physics 19 (13): 9075–9085.
APA
Joos, J., Lejaeghere, K., Korthout, K., Feng, A., Poelman, D., & Smet, P. (2017). Charge transfer induced energy storage in CaZnOS:Mn : insight from experimental and computational spectroscopy. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 19(13), 9075–9085.
Vancouver
1.
Joos J, Lejaeghere K, Korthout K, Feng A, Poelman D, Smet P. Charge transfer induced energy storage in CaZnOS:Mn : insight from experimental and computational spectroscopy. PHYSICAL CHEMISTRY CHEMICAL PHYSICS. 2017;19(13):9075–85.
MLA
Joos, Jonas, Kurt Lejaeghere, Katleen Korthout, et al. “Charge Transfer Induced Energy Storage in CaZnOS:Mn : Insight from Experimental and Computational Spectroscopy.” PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19.13 (2017): 9075–9085. Print.
@article{8519876,
  abstract     = {CaZnOS: Mn2+ is a rare-earth-free luminescent compound with an orange broadband emission at 612 nm, featuring pressure sensing capabilities, often explained by defect levels where energy can be stored. Despite recent efforts from experimental and theoretical points of view, the underlying luminescence mechanisms in this phosphor still lack a profound understanding. By the evaluation of thermoluminescence as a function of the charging wavelength, we probe the defect levels allowing energy storage. Multiple trap depths and trapping routes are found, suggesting predominantly local trapping close to Mn2+ impurities. We demonstrate that this phosphor shows mechanoluminescence which is unexpectedly stable at high temperature (up to 200 degrees C), allowing pressure sensing in a wide temperature range. Next, we correlate the spectroscopic results with a theoretical study of the electronic structure and stability of the Mn defects in CaZnOS. DFT calculations at the PBE+U level indicate that Mn impurities are incorporated on the Zn site in a divalent charge state, which is confirmed by X-ray absorption spectroscopy (XAS). Ligand-to-metal charge transfer (LMCT) is predicted from the location of the Mn impurity levels, obtained from the calculated defect formation energies. This LMCT proves to be a very efficient pathway for energy storage. The excited state landscape of the Mn2+ 3d(5) electron configuration is assessed through the spin-correlated crystal field and a good correspondence with the emission and excitation spectra is found. In conclusion, studying phosphors at both a singleparticle level (i.e. via calculation of defect formation energies) and a many-particle level (i.e. by accurately localizing the excited states) is necessary to obtain a complete picture of luminescent defects, as demonstrated in the case of CaZnOS: Mn2+.},
  author       = {Joos, Jonas and Lejaeghere, Kurt and Korthout, Katleen and Feng, Ang and Poelman, Dirk and Smet, Philippe},
  issn         = {1463-9076},
  journal      = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS},
  keyword      = {luminescence,mechanoluminescence,manganese,crystal field theory,DFT,modeling,charge transfer,DENSITY-FUNCTIONAL THEORY,RARE-EARTH IONS,VIBRONIC SPECTRA,AB-INITIO,LUMINESCENCE PROPERTIES,ALKALI-HALIDES,LIGAND-FIELD,PHOSPHORS,1ST-PRINCIPLES,LANTHANIDE},
  language     = {eng},
  number       = {13},
  pages        = {9075--9085},
  title        = {Charge transfer induced energy storage in CaZnOS:Mn : insight from experimental and computational spectroscopy},
  url          = {http://dx.doi.org/10.1039/c7cp00285h},
  volume       = {19},
  year         = {2017},
}

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