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

kurt — Sat, 24 Sep 2016 09:46:09 +0000

J.J. Joos, K. Lejaeghere, K. Korthout, A. Feng, D. Poelman, P. F. Smet

Physical Chemistry Chemical Physics (PCCP)

19 (13), 9075-9085

2017

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 °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+ 3d5 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 single-particle 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+.

Open Access version available at UGent repository

Gold Open Access

DOI

http://dx.doi.org/10.1039/C7CP00285H

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c7cp00285h.pdf

Mn impurities in CaZnOS: insight from luminescence spectroscopy and density functional theory

kurt — Fri, 26 Jan 2018 07:53:23 +0000

J.J. Joos, K. Lejaeghere, K. Korthout, A. Feng, D. Poelman, P.F. Smet

ISBN/ISSN:

Talk

Conference / event / venue

Workshop on Charge Trapping Defects in Semiconductors and Insulators

York, UK

Monday, 20 March, 2017 to Tuesday, 21 March, 2017

Center for Molecular Modeling - K. Korthout

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

Abstract

DOI

Private attachment

Mn impurities in CaZnOS: insight from luminescence spectroscopy and density functional theory

Conference / event / venue