Pigments and Near-Infrared Phosphors Based on Mn<sup>5+</sup>
The optical properties of Mn<sup>5+</sup> ions, which are responsible for the intense green–turquoise–blue coloration of Mn<sup>5+</sup>-based pigments and the near-infrared emission of phosphors, are the focus of this article. Mn<sup>5+</sup> ions enter crystalli...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-02-01
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| Series: | Nanomaterials |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2079-4991/15/4/275 |
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| Summary: | The optical properties of Mn<sup>5+</sup> ions, which are responsible for the intense green–turquoise–blue coloration of Mn<sup>5+</sup>-based pigments and the near-infrared emission of phosphors, are the focus of this article. Mn<sup>5+</sup> ions enter crystalline matrices in four-fold coordinated positions and can maintain their 5+ valence state when crystalline hosts meet the conditions described in this work. Mn<sup>5+</sup> ions have [Ar]3d<sup>2</sup> electronic configuration and always experience a strong crystal field due to a high electric charge; therefore, their lower electronic states have the <sup>3</sup>A<sub>2</sub> < <sup>1</sup>E < <sup>1</sup>A<sub>1</sub> < <sup>3</sup>T<sub>2</sub> < <sup>3</sup>T<sub>1</sub> progression in energy. We present the properties of several Mn<sup>5+</sup>-based pigments and discuss the electronic transitions responsible for their coloration. Specifically, we show that the color is determined by the spin-allowed <sup>3</sup>A<sub>2</sub> → <sup>3</sup>T<sub>1</sub>(<sup>3</sup>F) absorption, which extends across the orange–red–deep red spectral region and is strongly influenced by crystal field strength. The narrow-band emission Mn<sup>5+</sup>-activated near-infrared phosphors arise from the spin-forbidden <sup>1</sup>E → <sup>3</sup>A<sub>2</sub> transition, whose energy is independent of the crystal field strength and determined by the nephelauxetic effect. We demonstrate the linear relationship between <sup>1</sup>E state energy and the nephelauxetic parameter <i>β</i><sub>1</sub> using Racah parameter literature data for Mn<sup>5+</sup> phosphors. Lastly, we address the recent applications of these Mn<sup>5+</sup> phosphors in luminescence thermometry. |
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| ISSN: | 2079-4991 |