Fluorescence temperature dependent behaviors of Eu3+/Mn4+ co-doping cubic and hexagonal ZnO-TiO2 compounds: Application in high sensitive optical thermometers

• Published in: Journal of alloys and compounds 2025-01, Vol.1010, p.177374, Article 177374
• Main Authors: Sun, Chengmei, Xu, Chengcheng, Ren, Wenzhen, Hu, Fengya, Yuan, Jun, Wang, Qingru, Xie, Yanru, Wang, Kai, Zhang, Dong
• Format: Article
• Language: English
• Subjects: Nanocrystals; Photoluminescence; Temperature sensing performances; ZnTiO3
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.177374

ZnTiO3:Eu3+,Mn4+ phosphors with hexagonal and cubic structure are synthesized by solvothermal method. The structure of ZnTiO3 depends on precursors and the annealing temperature. Inverse spinel Zn2TiO4 phase reveals the highest thermostability compared with cubic ZnTiO3 and hexagonal ZnTiO3 phases. The different phases of ZnTiO3 crystals exhibit different photoluminescence properties. The forbidden transition of 4A2g→2T2g for Mn4+ is observed in Zn2TiO4 and hexagonal ZnTiO3 (h-ZnTiO3) due to the decreased symmetry. The zero photon line (ZPL) assigned to 2Eg→4A2g transition of Mn4+ is absent in all type ZnTiO3 phases. A sharp emission peak at 714 nm assigned to ν6 (Stokes emission) mode of Mn4+ in h-ZnTiO3 is present when the temperature was below 270 K, and increases sharply in intensity with the temperature decreasing. The similar PL spectra of cubic ZnTiO3 and Zn2TiO4 co-doped with Eu3+ and Mn4+ show a wide emission band composed of Stokes and anti-Stokes modes. The calculated nephelauxetic parameter increases from 0.84 to 1.03 and 1.18 for Mn4+ in h-ZnTiO3, cubic ZnTiO3 and Zn2TiO4, respectively, indicating the covalency decreasing, which causes the red shift of ZPL in h-ZnTiO3. The Mn4+ emissions show stronger temperature dependence than that of Eu3+, especially for that in h-ZnTiO3 matrix. Based on the fluorescence intensity ratio between IEu3+ and IMn4+, the highest relative temperature sensitivity of 2.46 %K−1 is observed in cubic ZnTiO3 (c-ZnTiO3) and Zn2TiO4. Under the excitation at 550 nm, the highest relative sensitivity of 2.9 %K−1 is achieved in c- and h-ZnTiO3 mixed phases. [Display omitted] ●ZnO-TiO2 system with hexagonal, cubic and inversion spinel structure were prepared.●New Emission assigned to Mn4+ in indirect band gap ZnTiO3 was present.●Hexagonal ZnTiO3 had strong covalency causing the red shift of zero photon line.●Mixtures of hexagonal and cubic ZnTiO3 had the highest temperature sensitivity.