Shen Liu

Highly Sensitive Dual-Phase Nanoglass-Ceramics Self-Calibrated Optical Thermometer

A strategy to achieve high sensitivity of noncontact optical thermometer via the structure design of nanoglass-ceramic and the usage of Ln(3+) (Ln = Eu, Tb, Dy) luminescence as reference signal and Cr(3+) emission as temperature signal was provided. Specifically, the synthesized dual-phase glass-ceramics were evidenced to enable spatially confined doping of Ln(3+) in the hexagonal GdF3 nanocrystals and Cr(3+) in the cubic Ga2O3 nanoparticles, being beneficial to suppressing detrimental energy transfer between Ln(3+) and Cr(3+) and thus significantly enhancing their luminescence. As a consequence, completely different temperature-sensitive luminescence of Ln(3+)4f → 4f transition and Cr(3+) 3d → 3d transition in the present glass-ceramic resulted in obvious variation of Cr(3+)/Ln(3+) fluorescence intensity ratio with temperature and strikingly high detecting temperature sensitivity of 15-22% per K. We believe that this preliminary study will provide an important advance in exploring other innovative optical thermometry.

Dual-activator luminescence of RE/TM:Y3Al5O12 (RE = Eu3+, Tb3+, Dy3+; TM = Mn4+, Cr3+) phosphors for self-referencing optical thermometry

Traditional optical temperature sensors based on the rare earth fluorescence intensity ratio of two thermally coupled energy states have intrinsic limitations such as low relative sensitivity and large detection error due to the requirement of a narrow energy gap. Herein, a strategy involving the use of rare earth and transition metal dual-emitting centers with completely different thermal-quenching behaviors has been developed to achieve high temperature sensitivity and good discrimination of signals. In particular, Eu3+/Mn4+:Y3Al5O12 with strikingly high absolute and relative sensitivities of 0.441 K−1 and 4.81% K−1 as well as a large energy gap of 2100 cm−1 was realized by taking advantage of Eu3+ luminescence as a reference signal and Mn4+ luminescence as a temperature signal. The versatility of the proposed strategy has been demonstrated by adopting other Tb3+/Mn4+, Dy3+/Mn4+, Eu3+/Cr3+ and Dy3+/Cr3+ dual-activator combinations. It is expected that this preliminary study will provide an important advance in exploring novel self-referencing optical thermometry with excellent performance.

Yb3+/Ln3+/Cr3+ (Ln = Er, Ho) doped transparent glass ceramics: crystallization, Ln3+ sensitized Cr3+ upconversion emission and multi-modal temperature sensing

Currently, efficient photon anti-Stokes (upconversion) luminescence is mostly limited to lanthanide (Ln3+) doped materials. There are a few reports on upconversion behaviors of transition-metal ions, whose (Stokes) emissions are known to be tunable by changing the crystal fields of the hosts. Herein, Yb/Ln/Cr (Ln = Er, Ho) tri-doped glass ceramics were fabricated by a melt-quenching route and subsequent glass crystallization, where Cr3+ dopants were evidenced to be incorporated into the precipitated LiGa5O8 nanocrystals and Ln3+ ions remained in the glass matrix. An intense Cr3+ upconversion luminescence assigned to the 2E → 4A2 transition was observed upon 980 nm laser excitation via energy transfer from Yb3+ sensitizers to Er3+ activators/bridging-centers and finally to Cr3+ emitting centers. Importantly, the investigated glass ceramics presented temperature-dependent upconversion fluorescence intensity ratios for Er3+ 2H11/2/4S3/2 thermally coupled states as well as Cr3+/Ln3+ non-thermally coupled states and temperature-sensitive upconversion decays of Cr3+ 2E/4A2 thermally coupled states, enabling their promising applications in self-calibrated multi-modal temperature sensing.

Phase structure control and optical spectroscopy of rare-earth activated GdF3 nanocrystal embedded glass ceramics via alkaline-earth/alkali-metal doping

Hexagonal to orthorhombic phase transformation of GdF3 nanocrystals in bulk glass ceramics was achieved through alkaline-earth/alkali-metal doping and crystallization temperature controlling. Structural characterizations and spectroscopic analyses of the Eu3+ probe evidenced the incorporation of rare earth emitting-centers into the precipitated GdF3 crystals among the glass matrix. In addition, the influence of phase evolution on the upconversion luminescence of Er3+/Yb3+ co-doped glass ceramics was systematically investigated and it was evidenced that the upconversion intensity of the orthorhombic GdF3 embedded glass ceramic was two orders of magnitude higher than that of the hexagonal GdF3 containing glass ceramic. Benefiting from greatly enhanced upconversion luminescence after glass crystallization, the present glass ceramic composites were demonstrated to have promising applications in optical temperature sensors as well as tunable displays.

Eu3+-Doped glass ceramics containing NaTbF4 nanocrystals: controllable glass crystallization, Tb3+-bridged energy transfer and tunable luminescence

Herein, hexagonal and cubic NaTbF4:Eu3+ nanocrystals embedded in transparent glass ceramics were successfully synthesized via a conventional melt-quenching technique followed by glass crystallization for the first time. Structural and spectroscopic characterizations evidenced the composition-dependent crystalline precipitation and the partition of Eu3+ dopants into the NaTbF4 host. In particular, the energy transfer mechanism from Tb3+ to Eu3+ was systematically investigated by photoluminescence spectra and decay curves, confirming that the energy transfer chain of Tb3+ → (Tb3+)n → quenchers in NaTbF4 nanocrystals was replaced by Tb3+ → (Tb3+)n → Eu3+ with the incorporation of Eu3+. The discrepant luminescence behaviors in terms of on-phase transformation were also studied. Furthermore, tunable emission could be achieved by merely adjusting the content of Eu3+, producing distinguishable emissions. As a consequence, it could be expected that NaTbF4:Eu3+ nanocrystals embedded in glass ceramics are promising candidates for applications in lightings and displays.