Mn--Cr dopant association in dilute co-doped ZnAl2O4 revealed by combined EPR and optical spectroscopy
Abstract
Efficient and durable phosphors made from abundant elements underpin energy-saving solid-state lighting, near-infrared light sources for sensing, and X-ray and biomedical imaging. Co-doping is a standard route to brighter phosphors, yet the fate of the co-dopants is rarely established. We combine quantitative electron paramagnetic resonance (EPR) spin counting with photoluminescence, photoluminescence excitation, and X-ray-excited spectroscopy across two dilute Mn/Cr co-doping series of hydrothermally grown ZnAl2O4 nanoparticles and show that the two ions can form an exchange-coupled, edge-sharing Cr--Mn defect complex, with Mn2+/4+ entering an octahedral site next to Cr3+. The octahedral Mn lifts the inversion symmetry of the Cr3+ site and strengthens its parity-forbidden absorption, enhancing the Cr3+ emission without energy transfer. The population of the defect complex follows the law of mass action, and above a threshold Mn concentration, Mn re-partitions into EPR-silent octahedral configurations that quench both emissions. Concentration optima in co-doped phosphors can thus reflect defect speciation, not only energy-transfer efficiency, which opens a structural design handle for brighter emitters.
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BibTeX
@misc{omondi2026mncr,
title = {{Mn--Cr dopant association in dilute co-doped $\mathrmZnAl_2O_4$ revealed by combined EPR and optical spectroscopy}},
author = {Apoko S. Omondi and Mátyás M. Rudolf and Nikoletta Jegenyés and Árpád Jakab and Gábor Bortel and Bence G. Márkus and Adam Gali and Dávid Beke},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.14262},
eprint = {2610.14262},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.14262},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Mn--Cr dopant association in dilute co-doped ZnAl_2O_4 revealed by combined EPR and optical spectroscopy
AU - Apoko S. Omondi
AU - Mátyás M. Rudolf
AU - Nikoletta Jegenyés
AU - Árpád Jakab
AU - Gábor Bortel
AU - Bence G. Márkus
AU - Adam Gali
AU - Dávid Beke
PY - 2026
DA - 2026/10/09
PB - arXiv
DO - 10.48550/arxiv.2610.14262
UR - https://arxiv.org/abs/2610.14262
AB - Efficient and durable phosphors made from abundant elements underpin energy-saving solid-state lighting, near-infrared light sources for sensing, and X-ray and biomedical imaging. Co-doping is a standard route to brighter phosphors, yet the fate of the co-dopants is rarely established. We combine quantitative electron paramagnetic resonance (EPR) spin counting with photoluminescence, photoluminescence excitation, and X-ray-excited spectroscopy across two dilute Mn/Cr co-doping series of hydrothermally grown ZnAl_2O_4 nanoparticles and show that the two ions can form an exchange-coupled, edge-sharing Cr--Mn defect complex, with Mn^2+/4+ entering an octahedral site next to Cr^3+. The octahedral Mn lifts the inversion symmetry of the Cr^3+ site and strengthens its parity-forbidden absorption, enhancing the Cr^3+ emission without energy transfer. The population of the defect complex follows the law of mass action, and above a threshold Mn concentration, Mn re-partitions into EPR-silent octahedral configurations that quench both emissions. Concentration optima in co-doped phosphors can thus reflect defect speciation, not only energy-transfer efficiency, which opens a structural design handle for brighter emitters.
ER -