EXCITON DYNAMICS OF ORTHORHOMBIC PHASE PbI2 EMBEDDED IN PbI2-PbBr2 MIXED CRYSTALS

2001 ◽  
Vol 15 (28n30) ◽  
pp. 3845-3848 ◽  
Author(s):  
J. TAKEDA ◽  
T. SAKAMOTO ◽  
T. ARAI ◽  
S. KURITA
Keyword(s):  
Luminescence Band ◽  
Stokes Shift ◽  
Orthorhombic Phase ◽  
Exciton State ◽  
Mixed Crystals ◽  
Luminescence Spectra ◽  
Relaxation Processes ◽  
Time Resolved ◽  
Decay Component ◽  
Reflection Peak

Reflection, time-integrated and time-resolved luminescence spectra have been measured in PbI 2(1-x) Br 2x(x≥0.5) mixed crystals in order to elucidate the excitonic properties and relaxation processes of orthorhombic phase PbI 2 embedded in the mixed crystals. The crystal structure of PbI 2(1-x) Br 2x above x=0.5 is orthorhombic and an observed new reflection peak (~2.5 × 104 cm -1) above x=0.5 is due to an excitonic state of orthorhombic phase PbI 2. On the excitation energy above 2.5 × 104 cm -1, a broad luminescence band with a large Stokes shift from the reflection peak was observed. This luminescence band is attributed to a self-trapped exciton state. The decay of the luminescence has two components. Based on an atomic excitation picture, the shorter decay component (≤10 ns ) is attributed to the allowed transition from 3P1 to 1S0. On the other hand, the longer decay component (~3 μ s ) might be due to the forbidden transition from 3P0 to 1S0.

2LO RESONANT RELAXATION OF EXCITON POLARITON INTO LONGITUDINAL EXCITON STATE IN β-ZnP2

2001 ◽  
Vol 15 (28n30) ◽  
pp. 3889-3892
Author(s):  
K. NAKAMURA ◽  
S. UMEMOTO ◽  
O. ARIMOTO
Keyword(s):  
Energy Dissipation ◽  
Luminescence Band ◽  
Exciton State ◽  
Relaxation Processes ◽  
Exciton Luminescence ◽  
Exciton Energy ◽  
Excitation Spectra ◽  
Exciton Polaritons ◽  
Nonradiative Processes

Efficiency dip is observed at 2LO phonon energy above the 1s longitudinal exciton energy in excitation spectra for 1s exciton luminescence band in β- ZnP 2 at 2K. This dip comes from the 2LO resonant relaxation of exciton polariton into the longitudinal exciton state which plays a role of the killer of exciton polaritons in β- ZnP 2. Increase of nonradiative processes is checked by the photocalorimetric (PC) measurement. The PC response is not affected by the resonant 2LO process. Relaxation processes of exciton polaritons and energy dissipation are discussed.

TIME-RESOLVED PHOTOLUMINESCENCE OF EXCITONS IN HgI2

2001 ◽  
Vol 15 (28n30) ◽  
pp. 3920-3923 ◽  
Author(s):  
N. OHNO ◽  
X. M. WEN
Keyword(s):  
Radiative Recombination ◽  
Luminescence Band ◽  
Broad Band ◽  
Relaxation Processes ◽  
Time Resolved ◽  
Carrier Lifetimes ◽  
Broad Luminescence Band ◽  
Donor Acceptor ◽  
Exciton Annihilation ◽  
Time Resolved Photoluminescence

The time-resolved photoluminescence (TRPL) of red HgI 2 single crystal has been measured to determine the carrier lifetimes and to reveal the energy relaxation of excitons. Sharp near-bandgap luminescence lines due to free and bound excitons are observed at 530 nm, and a broad luminescence band appears at 630 nm at low temperatures. TRPL experiments of the near-bandgap luminescence have revealed that the luminescence comprise fast (30 to 200 ps) and slow (100 to 400 ps) decay components, showing several relaxation processes in free and bound exciton annihilation. TRPL of the broad band at 630 nm has shown that the luminescence is ascribed to the radiative recombination of donor-acceptor (DA) pairs.

SELF-TRAPPED EXCITONS IN ORTHORHOMBIC SnBr2

2001 ◽  
Vol 15 (28n30) ◽  
pp. 4009-4012 ◽  
Author(s):  
Y. YAMASAKI ◽  
N. OHNO
Keyword(s):  
Time Dependence ◽  
Low Temperatures ◽  
Luminescence Band ◽  
Radiative Decay ◽  
Time Resolved ◽  
Tunneling Recombination ◽  
Exciton Region ◽  
Time Resolved Photoluminescence ◽  
Stokes Shifts ◽  
2.5 Ev Luminescence

Luminescence properties of SnBr 2 have been studied to reveal the photo-excited exciton relaxation process. Two types of luminescence with large Stokes shifts are found at low temperatures; the 2.2-eV luminescence band produced under the photo-excitation in the first exciton region, and the 2.5-eV luminescence band stimulated by photons with energies above the bandgap. The time-resolved photoluminescence measurements have revealed that the 2.2-eV luminescence comprises fast (1.2 μs) and slow (6.4 μs) exponential decay components, whereas the 2.5-eV luminescence shows the time dependence of I(t)∞ t-0.9. These results suggest that the former band is attributed to the radiative decay of self-trapped excitons, and the latter band would originate from tunneling recombination of holes with the STEL as in the case of lead halides.

Time-Resolved Luminescence Spectra of Dosimeter Glasses

1990 ◽  
Vol 29 (Part 1, No. 5) ◽  
pp. 948-949 ◽  
Author(s):  
Tadaki Miyoshi
Keyword(s):  
Luminescence Spectra ◽  
Time Resolved

scholarly journals Dynamics of Anomalous Temperature-Induced Emission Shift in MOCVD-grown (Al, In)GaN Thin Films

2000 ◽  
Vol 5 (S1) ◽  
pp. 796-802 ◽  
Author(s):  
Yong-Hoon Cho ◽  
G. H. Gainer ◽  
J. B. Lam ◽  
J. J. Song ◽  
W Yang ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Stokes Shift ◽  
Energy Shift ◽  
Peak Position ◽  
Time Resolved ◽  
Temperature Range ◽  
Al Content ◽  
Peak Energy ◽  
Emission Behavior ◽  
Pl Intensity

We present a comprehensive study of the optical characteristics of (Al, In)GaN epilayers measured by photoluminescence (PL), integrated PL intensity, and time-resolved PL spectroscopy. For not only InGaN, but also AlGaN epilayers with large Al content, we observed an anomalous PL temperature dependence: (i) an “S-shaped” PL peak energy shift (decrease-increase-decrease) and (ii) an “inverted S-shaped” full width at half maximum (FWHM) change (increase-decrease-increase) with increasing temperature. Based on time-resolved PL, the S shape (inverted S shape) of the PL peak position (FWHM) as a function of temperature, and the much smaller PL intensity decrease in the temperature range showing the anomalous emission behavior, we conclude that strong localization of carriers occurs in InGaN and even in AlGaN with rather high Al content. We observed that the following increase with increasing Al content in AlGaN epilayers: (i) a Stokes shift between the PL peak energy and the absorption edge, (ii) a redshift of the emission with decay time, (iii) the deviations of the PL peak energy, FWHM, and PL intensity from their typical temperature dependence, and (iv) the corresponding temperature range of the anomalous emission behavior. This indicates that the band-gap fluctuation responsible for these characteristics is due to energy tail states caused by non-random inhomogeneous alloy potential variations enhanced with increasing Al content.

scholarly journals Luminescence in lanthanum-gallium tantalate

2018 ◽  
Vol 4 (3) ◽  
pp. 97-101
Author(s):  
Oleg A. Buzanov ◽  
Nina S. Kozlova ◽  
Nikita A. Siminel ◽  
Evgeniya V. Zabelina
Keyword(s):  
Stokes Shift ◽  
Luminescent Properties ◽  
Luminescence Spectra ◽  
Absorption Bands ◽  
Argon Gas ◽  
Complex Process ◽  
Growth Atmosphere ◽  
Luminescence Peak ◽  
Integral Absorption ◽  
20 Nm

The optical and luminescent properties of undoped La3Ga5.5Ta0.5O14 lanthanum- gallium tantalate crystals grown in different atmospheres of pure argon gas and argon gas with different oxygen percentages have been studied. The optical absorption α(λ) spectra that characterize integral absorption and reflection have been measured in the 250–700 nm region. The spectral absorption functions have been calculated from the measured α(λ) spectra using the Kubelka–Munk formula. Luminescence has been observed in all the test specimens over a wide spectral region (375 to 650 nm) at 95 and 300 K. The luminescence spectra of the test crystals have a fine dispersed pattern represented by low-intensity discrete luminescence peaks. The 95 K luminescence peak maxima are more pronounced and shifted towards shorter wavelengths by ~16 nm (~0.1 eV) relative to the respective room temperature peaks. The crystal growth atmosphere has been demonstrated to largely affect the luminescent properties of the crystals: the higher the oxygen concentration in the growth atmosphere, the lower the luminescence intensity due to concentration quenching, the luminescence peak maxima shifting towards longer wavelengths. The positions of discrete luminescence peaks have been shown to correlate with the main 420 and 480 nm absorption bands with the respective ~20 nm (~0.2 eV) Stokes shift for crystals grown in different atmospheres. The luminescence in lanthanum-gallium tantalate crystals is a complex process involving several luminescence mechanisms.

Luminescence Spectra of Pyrene-Perylene Mixed Crystals

1967 ◽  
Vol 22 (3) ◽  
pp. 926-926 ◽  
Author(s):  
Yasuhiro Ishii ◽  
Atsuo Matsui
Keyword(s):  
Mixed Crystals ◽  
Luminescence Spectra

Spin-Gitter-Relaxation im Triplett-Zustand von Chinoxalin in Perdeutero-Naphthalin und zwei ähnlichen Mischkristallen

1975 ◽  
Vol 30 (6-7) ◽  
pp. 754-770 ◽  
Author(s):  
U. Konzelmann ◽  
D. Kilpper ◽  
M. Schwoerer
Keyword(s):  
Triplet State ◽  
Deep Trap ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Mixed Crystals ◽  
Spin Lattice Relaxation ◽  
Relaxation Processes ◽  
Shallow Trap ◽  
Field Range ◽  
Spin Lattice

Abstract Spin Lattice Relaxation in the Triplet State of Qainoxaline in Perdeuteronaphthalene and of two Similar Mixed Crystals The spin lattice relaxation in the excited triplet state of three mixed crystals was investigated: Quinoxaline in perdeutero-naphthalene, quinoxaline in naphthalene (X-traps) and quinoxaline in durene. They differ by the depth of their traps, which are shallow (90 cm -1), very shallow (60 cm -1) and deep (6600 cm -1), respectively. In order to identify the relaxation processes and the relaxation mechanism, the experiments were performed in the large magnetic field range be-tween 0.2 T and 5.4 T. By use of a non-resonant optical method and by ESR and ODMR it could be shown that at high fields the direct process (emission of resonant phonons) is the only efficient process up to 4.2 K. At low fields Raman-processes are dominant. Thereby the spin lattice relaxation probability per unit time, w, increases with the ninth power of the temperature in the shallow trap systems and with the fifth power in the deep trap system. By the analysis of the very strong anisotropy of w it could be shown that the efficient relaxation mechanism in the shallow trap systems is a guest-host-interaction modulated by phonons.

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