Browsing by Author "Han, T. C."

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Biexciton emission from sol-gel ZnMgO nanopowders
(2010-05-10)
Chia, C. H.
;
Lai, Y. J.
;
Hsu, W. L.
;
Han, T. C.
;
Chiou, J. W.
We studied the power-dependent photoluminescence of Zn(1-x)Mg(x)O nanopowders grown by sol-gel method, at temperature T = 100 K. At moderate optical pumping intensity, a nonlinear emission band due to the radiative recombination of free biexcitons was detected. We found that the free biexciton binding energies of Zn(1-x)Mg(x)O nanopowder (0.01 <= x <= 0.05) are nearly constant (13.5 +/- 1.5 meV). (C) 2010 American Institute of Physics. [doi:10.1063/1.3428780]
High-excitation effect on photoluminescence of sol-gel ZnO nanopowder
(2010-02-22)
Chia, C. H.
;
Lai, Y. J.
;
Han, T. C.
;
Chiou, J. W.
;
Hu, Y. M.
We studied the power-dependent photoluminescence of ZnO nanopowder grown by sol-gel method at low temperature. At moderate optical pumping intensity, two nonlinear emission bands due to the radiative recombination of free biexciton and the inelastic exciton-exciton scattering were detected. We found that the threshold of the excitation density for the emergence of the nonlinear emission bands is low (< 18 W/cm(2)) in sol-gel ZnO nanopowders.
Lattice Dynamics and Crystalline Properties of Wurtzite Zn(1-x)Mg(x)O Powders under High Pressure
(2011-10-13)
Lin, Y. C.
;
Tseng, C. L.
;
Chou, W. C.
;
Chia, C. H.
;
Han, T. C.
This investigation systematically studies the lattice dynamics and crystalline properties in Zn(1-x)Mg(x)O using high-pressure Raman spectroscopy. The incorporation of Mg and the application of external pressure cause distinct phonon vibrational behaviors in ZnO. Accordingly, the 202.7, 332.7, and 511.5 cm(-1) phonons, which have been controversially assigned, can be conclusively identified. Detailed Raman spectra reveal that the metallic phase transition of ZnO is complete by around 13.2 GPa, which pressure is found to decrease as the Mg content increases. Upon pressure release, an unusual hysteresis effect (>10.0 GPa) in Zn(1-x)Mg(x)O is observed. The degree of crystal ionicity and anisotropy importantly affects the phase transition pressure of Zn(1-x)Mg(x)O. Under ambient conditions, ZnO becomes more ionic upon the incorporation of Mg and becomes more covalent under higher pressure. These results are caused by the interplay between the pressure dependence of the high-frequency dielectric constant and Born's transverse dynamical effective charge. The E(1)-A(1) splitting of the longitudinal and transverse optical phonons is analyzed, yielding insight into the pressure-dependent crystal anisotropy of Zn(1-x)Mg(x)O.
Lattice Dynamics and Crystalline Properties of Wurtzite Zn1-xMgxO Powders under High Pressure
(2011-10-13)
Lin, Y. C.
;
Tseng, C. L.
;
Chou, W. C.
;
Chia, C. H.
;
Han, T. C.
This investigation systematically studies the lattice dynamics and crystalline properties in Zn1-xMgxO using high-pressure Raman spectroscopy. The incorporation of Mg and the application of external pressure cause distinct phonon vibrational behaviors in ZnO. Accordingly, the 202.7, 332.7, and 511.5 cm(-1) phonons, which have been controversially assigned, can be conclusively identified. Detailed Raman spectra reveal that the metallic phase transition of ZnO is complete by around 13.2 GPa, which pressure is found to decrease as the Mg content increases. Upon pressure release, an unusual hysteresis effect (>10.0 GPa) in Zn1-xMgxO is observed. The degree of crystal ionicity and anisotropy importantly affects the phase transition pressure of Zn1-xMgxO. Under ambient conditions, ZnO becomes more ionic upon the incorporation of Mg and becomes more covalent under higher pressure. These results are caused by the interplay between the pressure dependence of the high-frequency dielectric constant and Born's transverse dynamical effective charge. The E-1-A(1) splitting of the longitudinal and transverse optical phonons is analyzed, yielding insight into the pressure-dependent crystal anisotropy of Zn1-xMgxO.
Size dependence of exciton-phonon coupling in sol-gel ZnMgO powders
(2011-03-15)
Chia, C. H.
;
Chen, J. N.
;
Han, T. C.
;
Chiou, J. W.
;
Lin, Y. C.
We found that the exciton-phonon coupling in the Zn(1-x)Mg(x)O powders (0.01 <= x <= 0.07) is greatly influenced by the crystalline-size. Two well-resolved photoluminescence (PL) bands due to recombination of free exciton and its longitudinal optical (LO)-phonon replicas enable us to analyze the relative intensities among free excitons, one-LO-phonon replicas, and two-LO-phonon replicas. As crystalline size increases, a larger enhancement of the PL-intensity ratio of a free exciton to its LO-phonon replicas was found compared to that of two LO-phonon replica to one-LO-phonon replica. (C) 2011 American Institute of Physics. [doi:10.1063/1.3563574]