Baojiu Chen

Temperature dependence of luminescent spectra and dynamics in nanocrystalline Y2O3:Eu3+

A temperature dependence for emission of Eu3+ in cubic nanocrystalline Y2O3:Eu3+ was studied in contrast with the polycrystalline powders. The emission intensity of Eu3+ decreased solely with elevated temperature under the excitation of a 580 nm light, while it had a maximum at a certain temperature under a 488 nm light. The experimental data were well fitted based on a theory considering both the thermal activated distribution of electrons among 7FJ and the thermal quenching effect. The results indicated that the thermal quenching rate in nanocrystals (NCs) was faster than that in the polycrystals. The nonradiative decay rate, wNR, the radiative transition rate, w0R, and the luminescent quantum efficiency (QE) were obtained according to the temperature dependence of fluorescence lifetime. It can be concluded that wNR and w0R both increase in NCs, and that QE decreases.

Fluorescence properties of trivalent europium doped in various niobate codoped glasses

A series of niobate–phosphate and niobate–silicate glasses doped with Eu3+ ions were prepared. The emissions, phonon-side band spectra, and fluorescence lifetimes of these glasses were studied and the intensity parameters of Eu3+ were obtained. The temperature dependence of emission intensity of the Eu3+ ion in these niobate glasses was investigated. The temperature-quenching rates were determined. The results indicate that in niobate glasses, as the concentration of Nb2O5 increases, the covalence becomes stronger, the symmetry becomes lower and the electron-phonon coupling strength becomes stronger. Thus, the lifetimes become shorter, and the nonradiative transition processes and the temperature-quenching effect become stronger.

Size-dependent electronic transition rates in cubic nanocrystalline europium doped yttria

Abstract In cubic nanocrystalline as well as polycrystalline Y 2 O 3 :Eu 3+ prepared by combustion, the radiative transition rate of 5 D 1 – 7 F 1 and the nonradiative relaxation rate of 5 D 1 – 5 D 0 were obtained by measuring the temperature-dependence of emission intensity and lifetime. The results indicate that the radiative and nonradiative rates both increase with decreasing particle size. The increase of radiative transition rate was attributed to the lower symmetry surrounding the Eu 3+ ions, while the increase of nonradiative relaxation rate to the additional nonradiative relaxation channels caused by surface defects.

Spectral difference between nanocrystalline and bulk Y2O3 : Eu3+

Abstract In this Letter spectral difference between nanocrystalline yttria doped with europium (Y2O3:Eu3+) and the bulk ones was reported. Besides a 580.6-nm line similar to that in the bulk Y2O3:Eu3+, a new broad excitation line at 579.9 nm was observed in the nanocrystals (NCs). The lifetime of the 579.9-nm line became slightly shorter than that of the 580.6-nm line. The 579.9-nm line was attributed to the Eu3+ ions near the surface of the NCs. Due to numerous surface defects, the crystal field on the surface degenerated, leading the energy levels of the electrons in 4f state to shift.

Infrared-to-violet upconversion from Yb3+ and Er3+ codoped amorphous fluoride film prepared by pulsed laser deposition

Yb3+–Er3+ codoped amorphous Zn0.3Al0.25Pb0.3Li0.09Yb0.1Er0.01F2.37 film has been prepared by pulsed-laser deposition. Violet, green, red, and ultraviolet upconversion emissions were observed under infrared excitation at 988 nm. In comparison with the upconversion of the target, the violet and ultraviolet emissions are enhanced greatly. The enhancement is attributed to the diminishing of the cross relaxation: 4G11/2→4F9/2 (Er3+): 2F7/2→2F5/2 (Yb3+) induced by the decrement of the structure parameter Ω2.

Ultraviolet light-induced spectral change in cubic nanocrystalline Y2O3:Eu3+

Abstract Ultraviolet light-irradiation induced spectral change was studied in cubic nanocrystalline Y 2 O 3 :Eu 3+ . Under the irradiation of the ultraviolet lights separated from xenon lamp, the excited charge transfer band of Eu 3+ decreased after irradiation. The smaller the particle size and the shorter the wavelength, the larger the spectral change. It was attributed to the local structural change surrounding Eu 3+ ions in/near the surface. Under the irradiation of the 266-nm pulsed laser, some Eu 3+ in nanoparticles was reduced to Eu 2+ .

Fluorescence properties of divalent and trivalent europium ions in aluminosilicate glasses

Optical absorption, fluorescence, excitation and time-resolved spectra, and fluorescence dynamics were studied in Eu2+- and Eu3+-codoped aluminosilicate glasses. The results indicated that the energy transfer occurred between Eu2+ and Eu3+ ions, in which the energy corresponding to the 4f65d to 8S7/2 transition of Eu2+ ions caused excitation of the Eu3+ ions to the 5DJ level. Some of the electrons in the ground state 7F0 were thermally excited into the 7F1 state at room temperature, and thermal populations of the 7F1 level had great effects on the spectral shape of the 5D0–7F2 emission. The effect of light irradiation at different wavelengths on fluorescence was systemically studied. The visible, ultraviolet and x-ray irradiation caused a decrease in the fluorescence of Eu2+ and/or Eu3+ ions. Frequency selective excitation experiments were performed at 10 K and room temperature. Instead of forming a spectral hole, the intensity of the 7F0–5D0 transition decreased as a whole. This was attributed to the interaction of Eu3+ ions with the two-level systems existing in the glass network.Optical absorption, fluorescence, excitation and time-resolved spectra, and fluorescence dynamics were studied in Eu2+- and Eu3+-codoped aluminosilicate glasses. The results indicated that the energy transfer occurred between Eu2+ and Eu3+ ions, in which the energy corresponding to the 4f65d to 8S7/2 transition of Eu2+ ions caused excitation of the Eu3+ ions to the 5DJ level. Some of the electrons in the ground state 7F0 were thermally excited into the 7F1 state at room temperature, and thermal populations of the 7F1 level had great effects on the spectral shape of the 5D0–7F2 emission. The effect of light irradiation at different wavelengths on fluorescence was systemically studied. The visible, ultraviolet and x-ray irradiation caused a decrease in the fluorescence of Eu2+ and/or Eu3+ ions. Frequency selective excitation experiments were performed at 10 K and room temperature. Instead of forming a spectral hole, the intensity of the 7F0–5D0 transition decreased as a whole. This was attributed to the int...

Theory on single molecule-photon cryocooler - Conception and quantum transition processes

The micro mechanism of anti-Stokes fluorescent cooling was investigated on molecular or ionic scale. A new conception of single molecule-photon cryocooler (SMPC) was given, and the smallest cryocooler in the world was predicted. We described SMPC and its running principle in detail. The quantum transition processes of SMPC and the largest cooling coefficient that SMPC can get in an optical transition were given. Also we studied the random property of SMPC in cooling processes. The thermodynamic behavior of single Yb3+ ion as a photon cryocooler was imitated.