Upconversion luminescence and favorable temperature sensing performance of eulytite-type Sr<sub>3</sub>Y(PO<sub>4</sub>)<sub>3</sub>:Yb<sup>3+</sup>/Ln<sup>3+</sup> phosphors (Ln=Ho, Er, Tm)
Creators: name: Liu, Weigang
name: Wang, Xuejiao
name: Zhu, Qi
name: Li, Xiaodong
name: Sun, Xudong
name: Li, Ji-Guang
Publisher: name: Taylor & Francis
Year: 2019
Subjects: subject: Biochemistry
subject: Space Science
subject: Physical Sciences not elsewhere classified
subject: Molecular Biology
subject: Physiology
subject: FOS: Biological sciences
subject: Chemical Sciences not elsewhere classified
subject: Biological Sciences not elsewhere classified
subject: Science Policy

description: Phase-pure eulytite-type Sr<sub>3</sub>Y<sub>0.88</sub>(PO<sub>4</sub>)<sub>3</sub>:0.10Yb<sup>3+</sup>,0.02Ln<sup>3+</sup> upconversion (UC) phosphors (Ln = Ho, Er, Tm) were synthesized <i>via</i> gel-combustion and subsequent calcination at 1250°C. Their UC luminescence, temperature-dependent fluorescence intensity ratio of thermally and/or non-thermally coupled energy levels, and performance of optical temperature sensing were systematically investigated. The phosphors typically exhibit green, orange-red and blue luminescence under 978 nm NIR laser excitation for Ln = Er, Ho and Tm, respectively, which were discussed from two- and three-photon processes. The 524 nm green (Er<sup>3+</sup>), 657 nm red (Ho<sup>3+</sup>) and 476 nm blue (Tm<sup>3+</sup>) main emissions were analyzed to have average decay times of ~52 ± 2, 260.6 ± 0.7 and 117 ± 1 μs, respectively. It was shown that (1) the Er<sup>3+</sup> doped phosphor has a better overall performance of temperature sensing with thermally coupled <sup>2</sup>H<sub>11/2</sub> and <sup>4</sup>S<sub>3/2</sub> energy levels, whose maximum absolute (<i>S</i>
 <sub>A</sub>) and relative (<i>S<sub>R</sub>
 </i>) sensitivities are ~5.07 × 10<sup>−3</sup> K<sup>−1</sup> at 523 K and ~1.16% at 298 K, respectively; (2) the Ho<sup>3+</sup> doped phosphor shows maximum <i>S</i>
 <sub>A</sub> and <i>S<sub>R</sub>
 </i> values of ~0.019 K<sup>−1</sup> (298–573 K) and 0.42% at 573 K for the non-thermally coupled energy pairs of <sup>5</sup>F<sub>5</sub>/(<sup>5</sup>F<sub>4</sub>,<sup>5</sup>S<sub>2</sub>) and <sup>5</sup>I<sub>4</sub>/<sup>5</sup>F<sub>5</sub>, respectively; (3) the Tm<sup>3+</sup> doped phosphor has a maximum <i>S</i>
 <sub>A</sub> of ~12.74 × 10<sup>−3</sup> K<sup>−1</sup> at 573 K for the non-thermally coupled <sup>3</sup>F<sub>2,3</sub>/<sup>1</sup>G<sub>4</sub> energy levels and a maximum <i>S<sub>R</sub>
 </i> of ~1.74% K<sup>−1</sup> at 298 K for the thermally coupled <sup>3</sup>F<sub>2,3</sub>/<sup>3</sup>H<sub>4</sub> levels. Advantages of the current phosphors in optical temperature sensing were also revealed by comparing with other typical UC phosphors. Phase-pure eulytite-type Sr<sub>3</sub>Y<sub>0.88</sub>(PO<sub>4</sub>)<sub>3</sub>:0.10Yb<sup>3+</sup>,0.02Ln<sup>3+</sup> upconversion (UC) phosphors (Ln=Ho, Er, Tm) were synthesized <i>via</i> gel-combustion, whose property and mechanism of UC luminescence and the performance of optical temperature sensing with thermally and/or non-thermally coupled energy levels were thoroughly investigated.