Predicting adsorbate entropy is an essential prerequisite
for surface
science, heterogeneous catalysis, and microkinetic modeling. The linear
correlation between adsorbate and gas-phase entropy has been widely
found in various experiments, and it is considered as a simple and
effective method to predict adsorbate entropy. In this work, the two-dimensional
(2D) ideal gas model was used to calculate adsorbate entropy with
the statistical thermodynamic method. The rotational entropy was obtained
by solving the Schrodinger equation for a two-dimensional rotator.
Combining the translational and vibrational entropy, an extended reversible
adiabatic equation for 2D ideal gas can be derived, which is identical
in form to the three-dimensional (3D) equation. Then the linear correlation
between the 2D and 3D entropy can be proved theoretically, and the
slope of this linear correlation is the heat capacity ratio. According
to the characteristics of vibrational contribution to the heat capacity,
the temperature is divided into three ranges, each of which has its
own linear correlation. From the statistical thermodynamic computation
data of benzene, perfect linear correlations can be fitted, and each
slope is much close to the predicted value from our derived equation.
The widely used Campbell–Sellers correlation matches our correlation
in the low temperature range. We predict that there may be another
linear correlation for different molecules in the medium temperature
range, which is more appropriate in most heterogeneous catalytic reactions.
A new phosphor of the type Gd Eu V O (x=0-1.0) was synthesized through the solid-state reaction ceramics method. A pure phase formation was verified by using X-ray powder diffraction measurements. The luminescence of Gd V O :Eu was investigated through optical and laser excitation spectroscopy. The luminescence curves were investigated in the temperature region 10 to 300 K. Gd V O shows a self-activated luminescence under excitation with UV- and near-UV light. The spectra, the decay lifetimes, and the thermal stability of Gd Eu V O (x=0.005-1.0) strongly depend on both the Eu concentration and the temperature. The tunable luminescence is realized by controlling the Eu -doping level to adjust the host energy-transfer efficiency from the VO groups to the Eu activators. At low Eu concentrations (<30 mol %), the intensity and lifetime show an unusual change with an increase of the temperature from 10-300 K, that is, the luminescence experiences a straightforward enhancement. The energy transfer from the VO group to the Eu ions could be accelerated with an increase of the temperature resulting in an unusual enhancement of the Eu luminescence and lifetime. However, the emission of the Eu ions decreased for highly Eu-doped samples (>30 mol %) with an increase of the temperature. The luminescence mechanism was discussed on the basis of the charge-transfer band of the Eu ions, the doping concentration, and the proposed microstructures in the lattices.
A novel blue-emitting phosphor, Li3Gd3Te2O12:Tm3+ for white light-emitting diodes (W-LEDs) was prepared by solid-state synthesis and its structure and luminescence properties were investigated. This phosphor shows a satisfactory blue performance (peak at 458 nm) due to the 1D2 → 3F4 transition of Tm3+ excited by 361 nm light. Investigation of Tm3+ content dependent emission spectra indicates that x = 0.03 is the optimum doping content of Tm3+ ions in the Li3Gd3Te2O12 host. The critical distance and the concentration quenching mechanism were also investigated. In particular, the color purity of as-prepared sample is close to that of the commercial blue phosphor BaMgAl10O17:Eu2+ (BAM:Eu2+). The present work suggests that the Li3Gd3Te2O12:Tm3+ phosphor is a potential blue-emitting candidate for the application in the near-UV WLEDs.
The dysprosium activating La3SbO7 white-emitting phosphors were prepared via solid-state route at 1350°C in air atmosphere and its photoluminescence properties were examined by X-ray diffraction (XRD) and photoluminescence spectra in details. La3SbO7:Dy3+ phosphor with excitation at 353 nm emitted blue light (490 nm) and yellow (580 nm) which were assigned to 4F9/2–6Hj/2 transitions (J=15, 13), respectively. Moreover, the transition 4F9/2–6H13/2 was the strongest emission intensity between two typical emission bands. The CIE of prepared phosphors entered into white region. The optimal emission intensity of the La3SbO7:Dy3+ luminescent materials was realized when x = 0.15 and the concentration quenching mechanism of Dy3+ has also been tested. And the La3SbO7:Dy3+ can be as a white-emitting phosphor applied in n-UV LEDs on results.
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