Fengfeng Chi

Structural characterization and temperature-dependent luminescence of CaF 2 :Tb 3+ /Eu 3+ glass ceramics

Abstract Tb 3+ /Eu 3+ co-doped transparent glass ceramics containing CaF 2 nanocrystals were successfully synthesized by high temperature melt-quenching method and subsequent heating. The structure and morphology of the samples were investigated by X-ray diffraction (XRD), transmittance electron microscopy (TEM), high resolution TEM (HRTEM) and selected area electron diffraction (SAED). The photoluminescence properties and energy transfer process from Tb 3+ to Eu 3+ of CaF 2 :Tb 3+ ,Eu 3+ phosphors were also investigated through excitation spectra and decay curves. In addition, the emission spectra of the glass ceramics in a wide temperature range from 21 to 320 K were recorded under the excitation of 485 nm. It was found that the fluorescence intensity ratios of Tb 3+ at 545 nm ( 5 D 4 → 7 F 5 ) to Eu 3+ at 615 nm ( 5 D 0 → 7 F 2 ) was highly temperature-dependent with an approximate linear relationship, and the temperature sensitivity was about 0.4%/K. It is expected that the investigated Tb 3+ /Eu 3+ co-doped CaF 2 glass ceramics may have prospective application in optical thermometry.

Trivalent Yb/Ho/Ce tri-doped core/shell NaYF 4 nanoparticles for tunable upconversion luminescence from green to red

Abstract Three types of β-NaYF 4 nanoparticles, uncoated core (NaYF 4 :Yb/Ho/Ce), single-layer coated core@shell (NaYF 4 :Yb/Ho/ Ce@NaYF 4 :Yb) and double-layer coated core@shell@shell (NaYF 4 :Yb/Ho@NaYF 4 :Yb@NaYF 4 :Yb) with Ce 3+ doped in core, first and second shell, respectively, were synthesized through solvothermal method to investigate the cross-relaxation between Ho 3+ and Ce 3+ for the tunable upconversion luminescence. By doping Ce 3+ into different layers with different doping concentrations, a systematical investigation on the tunable upconversion luminescence from green to red was conducted. The results showed that a remarkable color tuning could be achieved from green to red when increasing the doping concentration of Ce 3+ in the same layer of Ho 3+ . And if Ce 3+ and Ho 3+ were separated in different layers, the color tuning would be depressed significantly due to the reduced cross-relaxation between Ho 3+ and Ce 3+ . Moreover, the UC emission intensity of core@shell and core@shell@shell was enhanced significantly compared with that of unmodified core nanoparticles.

Synthesis and thermometric properties of Yb 3+ -Er 3+ co-doped K 2 GdF 5 up-conversion phosphors

Abstract Yb3+-Er3+ co-doped K2GdF5 up-conversion phosphor was successfully synthesized by a solid-state reaction method. The phase purity and structure of the sample were characterized by powder X-ray diffraction. The sample emitted orange light at room temperature and its up-conversion spectra at different temperatures were recorded under the excitation of a 980 nm diode laser. The energy transfer from Yb3+ to Er3+ notably enhanced the up-conversion luminescence intensity. The possible up-conversion mechanisms and processes were proposed based on the power dependence of the luminescence intensities. The temperature-dependent up-conversion luminescence and temperature sensing performances of the sample were discussed according to the fluorescence intensity ratio of green emissions originating from 2H11/2/4S3/2→4I15/2 transitions of Er3+ in the range from 307 K to 570 K under the excitation of 980 nm laser with power of 260 mW. The dependence of the fluorescence intensity ratio on temperature was fitted with an exponential function and the effective energy difference obtained was 690 cm−1, which further gave a relative temperature sensitivity of 1.1%/K at 307 K. The results suggested that the Yb3+-Er3+ co-doped K2GdF5 sample is a promising candidate for optical temperature sensor.

A self-activated MgGa2O4 for persistent luminescence phosphor

The spinel compound MgGa2O4 synthesized by a high temperature solid state reaction method exhibits a long and bright blue persistent luminescence with UV source excitation. The blue afterglow can be observed by naked eyes in the dark for at least 10 min. The photoluminescence spectra of the MgGa2O4 host reveal a broad emission band in the range of 325–650 nm with the main peak at 424 nm and the secondary weaker peak at 480 nm under 265 nm excitation. The thermoluminescence curve disclosed a broad distribution of the traps existent in the MgGa2O4 host. In addition, a systematic investigation about the photoluminescence and the thermoluminescence of Mn2+ or Cr3+ single doped MgGa2O4 was also conducted to examine the doping effect. It is found that the distribution of traps responsible for thermoluminescence was disturbed significantly by different doping. A mechanism of the emission and the persistent luminescence is proposed in the light of the comparison of the results of the undoped host and the doped samples. The results indicate that the various vacancy defects in the MgGa2O4 host play an important role in its persistent luminescence.The spinel compound MgGa2O4 synthesized by a high temperature solid state reaction method exhibits a long and bright blue persistent luminescence with UV source excitation. The blue afterglow can be observed by naked eyes in the dark for at least 10 min. The photoluminescence spectra of the MgGa2O4 host reveal a broad emission band in the range of 325–650 nm with the main peak at 424 nm and the secondary weaker peak at 480 nm under 265 nm excitation. The thermoluminescence curve disclosed a broad distribution of the traps existent in the MgGa2O4 host. In addition, a systematic investigation about the photoluminescence and the thermoluminescence of Mn2+ or Cr3+ single doped MgGa2O4 was also conducted to examine the doping effect. It is found that the distribution of traps responsible for thermoluminescence was disturbed significantly by different doping. A mechanism of the emission and the persistent luminescence is proposed in the light of the comparison of the results of the undoped host and the doped sa...

Enhanced 5D0 → 7F4 transition and optical thermometry of garnet type Ca3Ga2Ge3O12:Eu3+ phosphors

The garnet type phosphors of Eu3+ doped Ca3Ga2Ge3O12 were synthesized via conventional solid state reaction techniques. The phase purity and luminescence properties of the fabricated phosphors were characterized by X-ray powder diffraction, photoluminescence excitation and emission spectra, temperature dependent emission spectra as well as luminescence decay curves. The phosphors show enhanced red emission from a 5D0 → 7F4 transition of Eu3+ under the excitation of 394 nm. The unusual 5D0 → 7F4 intensity was explained by structural analysis. The emission intensity of the phosphors increases with the concentration of Eu3+ until the quenching concentration of 10 mol%. Excited by a pulsed laser of wavelength 610.8 nm, the emission intensity of the 5D0 → 7F4 transition increases monotonously as the temperature increases in the range of 160–360 K. The temperature dependent fluorescence behavior was investigated. The relative sensitivity reaches the maximum value of 3.66% K−1 at 160 K and reaches 1.04% K−1 at 300 K. The results show that the garnet type Ca3Ga2Ge3O12:Eu3+ phosphor is a promising material for the application of optical thermometry.