Erlei Wang,Kun Feng,Jia Li,Xiaodong Zhou,Xianke Sun
A series of Bi 3+ /Tb 3+ /Eu 3+ doped NaYGeO 4 phosphors were synthesized via the solid state sintering at 1300 °C for 3 h. The phase and luminescence performance of the synthesized phosphors were investigated. The Bi 3+ , Tb 3+ and Eu 3+ single doped NaYGeO 4 phosphors show the prominent blue, green and red emission, respectively. And the emission shows obvious dependence on doping concentration and excitation wavelength. The Bi 3+ → Tb 3+ /Eu 3+ energy transfers were confirmed by the luminescence characteristics of the Bi 3+ /Tb 3+ , Bi 3+ /Eu 3+ and Bi 3+ /Tb 3+ /Eu 3+ doped NaYGeO 4 phosphors. The Bi 3+ → Tb 3+ energy transfer in the NaYGeO 4 :Bi 3+ /Tb 3+ phosphors leads to the tunable emission from the blue to cyan-green light region and the Bi 3+ → Eu 3+ energy transfer in the NaYGeO 4 :Bi 3+ /Eu 3+ phosphors leads to the tunable emission from the blue to purple-red light region. But in the NaYGeO 4 :Bi 3+ /Tb 3+ /Eu 3+ phosphors, the Bi 3+ → Tb 3+ /Eu 3+ energy transfers lead to the tunable emission from the blue to yellow light region through the white light region. From the luminescence characteristics of the Bi 3+ /Tb 3+ /Eu 3+ doped NaYGeO 4 phosphors, the energy transfer mechanisms were speculated.
Hui Zeng,Yangbo Wang,Xiaoyi Zhang,Xiangbing Bu,Zongyi Liu,Huaiyong Li
Excitation wavelength controllable lanthanide upconversion allows for real-time manipulation of luminescent color in a composition-fixed material, which has been proven to be conducive to a variety of applications, such as optical anti-counterfeiting and information security. However, current available materials highly rely on the elaborate core–shell structure in order to ensure efficient excitation-dependent energy transfer routes. Herein, multicolor upconversion luminescence in response to both near-infrared I and near-infrared II (NIR-I and NIR-II) excitations is realized in a novel but simple NaYGeO4:Yb3+/Er3+phosphor. The remarkably enhanced red emission ratio under 1532 nm excitation, compared with that under 980 nm excitation, could be attributed to the Yb3+-mediated cross-relaxation energy transfers. Moreover, multi-wavelength excitable temperature-dependent (295–823 K) upconversion luminescence realizes a ratiometric thermometry relying on the thermally coupled levels (TCLs) of Er3+. Detailed investigations demonstrate that changing excitation wavelength makes little difference for the performances of TCL-based ratiometric thermometry of NaYGeO4:Yb3+/Er3+. These findings gain more insights to manipulate cross-relaxations for excitation controllable upconversion in single activator doped materials and benefit the cognition of the effect of excitation wavelength on ratiometric luminescence thermometry.
Lanthanide NIR-II luminescence free from thermal quenching is attractive for various applications at elevated temperatures. Here, we present a thermal enhancement of Er 3+ NIR-II luminescence based on the synergy of phonon assisted Er 3+ -Er 3+ cross relaxations and controllable Er 3+ -Ho 3+ energy transfer. The lattice expansion of NaYGeO 4 olivine phosphor upon heating (298–823 K) suppresses the Er 3+ -Ho 3+ energy transfer and leads up to 46.1 times enhancement of Er 3+ NIR-II luminescence under 379 nm excitation. The NIR-II luminescence evolution as increasing temperature allows dual-mode ratiometric thermometry, i.e., luminescence intensity ratios (LIRs) based on Er 3+ 4 I 13/2 Stark sublevels and on Er 3+ 4 I 13/2 and Ho 3+ 5 I 6 levels. Obtained relative sensitivities above 0.46% K ‒1 over a broad temperature range of 298–673 K with a maximum of 2.32% K -1 suggest NaYGeO 4 :Er 3+ /Ho 3+ phosphor as a promising NIR-II luminescence thermometer. Moreover, this research offers an available perspective for designing thermal-enhanced NIR luminescence in ordinary thermal expansion materials.
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