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<p>A new ratiometric Boltzmann thermometry approach is presented for the narrow-line red-emitting bright phosphor Al<sub>0.993</sub>Cr<sub>0.007</sub>B<sub>4</sub>O<sub>6</sub>N. It relies on thermalization between the two excited states <sup>2</sup><i>E</i><sub><i>g</i></sub>(<sup>2</sup>G) and <sup>2</sup><i>T</i><sub>1<i>g</i></sub>(<sup>2</sup>G) of Cr<sup>3+</sup> with an energy gap of 620 cm<sup>−1</sup> for optimized thermometry at room temperature. It is shown that nonradiative coupling between these excited states is very fast, with rates in the order of several µs<sup>−1</sup>. Due to the comparably slow radiative decay (<i>k</i><sub>r</sub> = 0.033 ms<sup>−</sup><sup>1</sup>) of the lowest excited <sup>2</sup><i>E</i><sub><i>g</i></sub>(<sup>2</sup>G) state, the dynamic working range of this Boltzmann thermometer for the deep red spectral range is exceptionally wide, between &lt;77 K and &gt;873 K, even outperforming the classic workhorse example of Er<sup>3+</sup>. At temperatures above 340 K, also spectrally well-resolved broad-band emission due to the spin-allowed <sup>4</sup><i>T</i><sub>2<i>g</i></sub>(<sup>4</sup>F) → <sup>4</sup><i>A</i><sub>2<i>g</i></sub>(<sup>4</sup>F) transition is detectable, which simultaneously offers a possibility of very sensitive (<i>S</i><sub>r</sub>(500 K) &gt; 2% K<sup>−1</sup>) ratiometric Boltzmann-type crossover thermometry for higher temperatures. These findings imply that Al<sub>0.993</sub>Cr<sub>0.007</sub>B<sub>4</sub>O<sub>6</sub>N is a particularly robust and bright red luminescent thermometer with a record-breaking dynamic working range for a luminescent transition metal ion.</p>

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Ratiometric Boltzmann thermometry with Cr3+ in strong ligand fields: Efficient nonradiative coupling for record dynamic working ranges

  • 期刊论文

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  • 发表日期：

    2025年11月25日

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  • Gülsüm Kinik,
  • Ingo Widmann,
  • Benedikt Bendel,
  • Hubert Huppertz,
  • Andries Meijerink,
  • Markus Suta

摘要

A new ratiometric Boltzmann thermometry approach is presented for the narrow-line red-emitting bright phosphor Al0.993Cr0.007B4O6N. It relies on thermalization between the two excited states 2Eg(2G) and 2T1g(2G) of Cr3+ with an energy gap of 620 cm−1 for optimized thermometry at room temperature. It is shown that nonradiative coupling between these excited states is very fast, with rates in the order of several µs−1. Due to the comparably slow radiative decay (kr = 0.033 ms−1) of the lowest excited 2Eg(2G) state, the dynamic working range of this Boltzmann thermometer for the deep red spectral range is exceptionally wide, between <77 K and >873 K, even outperforming the classic workhorse example of Er3+. At temperatures above 340 K, also spectrally well-resolved broad-band emission due to the spin-allowed 4T2g(4F) → 4A2g(4F) transition is detectable, which simultaneously offers a possibility of very sensitive (Sr(500 K) > 2% K−1) ratiometric Boltzmann-type crossover thermometry for higher temperatures. These findings imply that Al0.993Cr0.007B4O6N is a particularly robust and bright red luminescent thermometer with a record-breaking dynamic working range for a luminescent transition metal ion.