eV Emission Band Research Articles

Thermoluminescence of chemical vapor deposited diamond film

Diamond films were synthesized by a chemical vapor deposition (CVD). Raman spectrum showed the diamond line at 1332 cm−1 and X-ray diffraction pattern exhibited a strong (111) peak of diamond. The scanning electron microscopy analysis showed that the CVD diamond film was grown to be unepitaxial crystallites with pyramidal hillocks. Three-dimensional thermoluminescence spectrum of CVD diamond film irradiated with X-ray produced one peak at 560 K and 430 nm. The main 560 K glow curve was caused by first order kinetics. Activation energy and escape frequency of the main peak were calculated to be 0.92∼1.05 eV and 3.4 × 107 s−1, respectively. The emission spectrum at 560 K was split into 1.63 eV, 2.60 eV, and 3.07 eV emission bands that were found to be associated with silicon-vacancy center, H3, and A center, respectively.

The interaction of deep traps in anion-defective α-Al 2O 3

This paper deals with the examination of thermoluminescence (TL) optical spectra (200–800 nm) for deep traps (DT) observed near 730 K (DT1) and 785 K (DT2) at β=2 K/s in dosimetric α-Al 2O 3 crystals. The DT1 spectrum consisted of two luminescence bands near 3.56 and 2.42 eV. The DT2 spectrum had one band near 2.95 eV. The 3.56 eV emission band was assigned to the F +-center luminescence and the 2.95 eV band to the F-center luminescence. The excitation spectra of the 2.42 eV emission band measured at RT had one peak at 4.11 eV. The intensity correlated with filling of deep traps. It was supposed that anion-defective corundum contained complex F-type centers. The state of those centers changed upon exposure to UV irradiation at a high temperature.

Relaxed Excited States Origin and Structure in Lead-Doped Caesium Bromide

Absorption, emission and excitation spectra, polarization and decay kinetics of luminescence and their temperature dependences have been studied at 4.2–300 K for several CsBr:Pb samples with various lead concentrations. The origin and structure of the relaxed excited states responsible for the 3.33, 2.8 and 2.43 eV emission bands have been discussed. It has been concluded that the relaxed excited state model proposed for Tl+-doped caesium halides and CsCl:Pb is not valid in case of CsBr:Pb. To establish the origin of the relaxed excited states in a CsBr:Pb crystal, the luminescence characteristics of CsBr:Pb have been compared with those reported for Cs4PbBr6, PbBr2 and CsPbBr3 bulk crystals. It has been assumed that owing to a strong interaction between Pb2+ and Br— ions, the molecular-like states, which are similar to the excited levels of some stable lead-related compounds, are responsible for the luminescence of CsBr:Pb crystals.

On the origin of the 2.8 eV blue emission in p-type GaN:Mg : A time-resolved photoluminescence investigation

The decay dynamics of the 2.8 eV emission band in p-type GaN was investigated using time-resolved photoluminescence spectroscopy. The luminescence intensity decays non-exponentially. The decay dynamics were consistent with donor-acceptor pair recombination for a random distribution of pair distances. Calculations using the Thomas-Hopfield model indicated that recombination involves deep donors and shallow acceptors.

Different character of the donor-acceptor pair-related 3.27 eV band and blue photoluminescence in Mg-doped GaN. Hydrostatic pressure studies

High-pressure measurements were employed to study mechanisms of (i) the 3.27 eV emission band (and phonon replicas) and (ii) 2.9--3.1 eV blue photoluminescence in different types of GaN:Mg samples. GaN layers with low Mg doping, grown on bulk GaN crystals and on sapphire substrates, were used to study the 3.27 eV uv band. This band results from donor-acceptor pair (DAP) recombination (with both impurities of shallow character). For high Mg doping resulting in blue light emission at about 3 eV, a bulk GaN crystal and a layer grown on sapphire were employed. For the all samples the pressure coefficient of the corresponding luminescence bands was measured at 77 K by means of the diamond anvil technique. The energy shift of the 3.27 eV band under hydrostatic pressure is used to determine the linear pressure coefficient characteristic for (shallow) DAP recombination. It has a value of about 35 meV/GPa, close to the pressure shift of the GaN band gap (about 40 meV/GPa). The 2.9--3.1 eV blue luminescence band exhibits much lower pressure coefficients of about 23 meV/GPa. It shows that the initial state of the blue emission has localized character in both types of GaN material and supplies a strong argument against models of radiative recombination in highly-Mg-doped/compensated GaN material that postulate an involvement of delocalized (shallow) electronic states as the initial states.

A spectroscopic study on SrS : Cu,Ag two-component electroluminescent phosphors

Under 4.507 eV excitation, the SrS : Cu,Ag thin films exhibited a saturated blue emission at 2.876 eV at room temperature and two additional emission bands at 3.443 and 2.398 eV were also observed at 10 K. By comparing with singly doped SrS : Cu and SrS : Ag, the two bands at 3.443 and 2.876 eV were assigned to the Ag emission bands and the 2.398 eV band to Cu emission. The enhancement of the 2.876 eV Ag emission band and the simultaneous suppression of the 2.398 eV Cu emission band are indicative of the presence of strong energy transfer from Cu to Ag ions in SrS : Cu,Ag. Low-temperature PLE spectrum of the 2.876 eV emission band was found to exhibit Cu excitation bands, confirming the presence of energy transfer from Cu to Ag. However, the energy transfer process from Cu to Ag exhibited anomalous properties that cannot be explained by the standard energy transfer theory. Therefore, instead of a Dexter-type energy transfer, electron transport was proposed as a possible coupling mechanism between the Cu and Ag ions in SrS.

Annealing Behavior of Layer Semiconductor p-InSe Doped with Hg

Photoluminescence and Hall effect measurements are carried out to study the annealing effect of Hg-doped InSe. The 1.237 eV emission band, which is associated with the transition between the donor level and the acceptor level at about 0.08 eV above the valence band, is enhanced by the increase of annealing temperature. We find that the acceptor level due to defects or defect complexes is formed by doping of Hg atoms and its concentration increases with increasing annealing temperature.

Relationship between crystallographic orientation and 3.42 eV emission bands in GaN grown by HVPE on Si substrate

The relationship between the 3.42 eV emission band in GaN and its crystallographic orientation was investigated. The peak position of the band shifts to lower energies with increase of the film thickness. The basal and/or pyramidal plane oriented GaN layers had a lower band intensity than those of prismatic plane oriented GaN films, and the polycrystalline structured GaN film showed both strong and neutral donor bound exciton band intensities. The band in GaN gradually shifted to lower energies with an increase of the luminescence intensity of the excitonic band indicating that the band in GaN is not at a fixed energy level, but depends upon its crystal structural qualities.

Time-Resolved Photoluminescence Study of GaAs/Ordered GaInP Interface under High Pressure

We have measured the photoluminescence (PL) spectra of GaAs/GaInP single quantum wells at pressure up to 5 GPa, and investigated the characteristics of the 1.46 eV deep emission band. It has a very long decay time of several hundred nanoseconds. In addition, unlike the emission from the GaAs well, a strong blue-shift of its peak energy with excitation intensity is observed. With increasing pressure, the emission peak shows a sublinear shift towards higher energy, while the GaAs quantum well exhibits a linear peak shift. The pressure dependence of the spectral peak position at higher excitation intensity tends to reflect that of the adjacent 1.49 eV emission band which has a faster decay profile. The pressure-dependent PL behavior at lower excitation intensity is rather similar to those observed for partially ordered GaInP alloys. These results suggest that the presence of ordered GaInP layers plays an important role in the radiative recombination at 1.46 eV and the deep emission is related to the transitions of electrons and holes localized at the GaAs/ordered GaInP heterointerface.

Self-trapped excitons in pure and Na- and Tl-doped caesium halides and the recombination luminescence

On the basis of a method used earlier to predict the off-centre relaxed triplet self-trapped excitons in alkali halides, similar systems in caesium halides are studied. This work confirms the expected off-centre relaxation along the [100] cubic axes with increasing magnitude in the order CsI, CsBr and CsCl. The calculated emission energies are in reasonable agreement with observed values. The well-known 2.95 eV emission band of CsI:Na has been studied as a tunnelling recombination between a close pair consisting of a VK centre and a Na atom. For a number of close-pair geometries the emission energies are close to 3 eV. The strong emission bands of CsI:Tl at 2.25 eV and 2.55 eV have been interpreted as arising from tunnelling recombination of close pairs each consisting of a Tl0 and a VK centre. The calculated emission energies and polarizations are discussed in conjunction with the experimental data.

Impurity Levels in p-Type Layered Semiconductor InSe Doped with Hg

Photoluminescence (PL) and Hall effect measurements have been made on Hg-doped p-type InSe. A broad emission band at 1.237 eV (77 K) is mainly observed on the PL spectra of samples doped with Hg and, in the range 0.02 to 0.1 at%, the PL intensity increases with increasing Hg concentration. From the temperature dependences of the PL intensity and peak energy position, we show that the 1.237 eV emission band is due to the transition between a shallow donor level and a deep acceptor level, at 0.07 eV above the valence band. The dominant acceptor level in the carrier transport measurements shows the same energy position as the radiative recombination center.

Impurity Levels in p-Type Layered Semiconductor InSe Doped with Hg

Photoluminescence (PL) and Hall effect measurements have been made on Hg-doped p-type InSe. A broad emission band at 1.237 eV (77 K) is mainly observed on the PL spectra of samples doped with Hg and, in the range 0.02 to 0.1 at%, the PL intensity increases with increasing Hg concentration. From the temperature dependences of the PL intensity and peak energy position, we show that the 1.237 eV emission band is due to the transition between a shallow donor level and a deep acceptor level, at 0.07 eV above the valence band. The dominant acceptor level in the carrier transport measurements shows the same energy position as the radiative recombination center.

On the luminescence of TlCdI 3 crystal

Optical-spectroscopy and spectral-kinetic parameter measurements of a perovskite-like TlCdI 3 crystal have been performed in the temperature range of 77–300 K. Exciting in the exciton absorption band ( E n =3.057 eV, n=1) at 77 K, the photoluminescence (PL) spectrum has two Gaussian shaped emission bands: a narrow band at 2.868 eV ( I) and a broad band at 2.370 eV ( II). The presence of a separate TlI phase is easily identified by means of 2.125 and 2.524 eV emission bands. The PL band I characterized by a 2.5 ns decay time is attributed to the cation bound exciton, and the PL band II is assigned to the anion self-trapped exciton. The latter band comprises the fast as well as the slow decay components. Their decay times at 77 K are: τ f=3.7 ns and t s=2.20 μs respectively. The thermal dependence of the latter permits the determination of the activation energy for nonradiative transitions (80.6 meV). The absolute luminescence light output for both PL bands abruptly diminishes when the temperature increases. In the case of X-ray excitation, the spectral position of the luminescence band has a strong dependence on foreign impurities. Excited by X-rays at 77 K, the TlCdI 3 crystal does not provide so many defect centers. Trap depths (0.26 and 0.34 eV) were obtained from the thermostimulated luminescence data.

Characterization of phosphorus in layer semiconductor GaSe

Radiative recombination mechanisms in P-doped p-GaSe have been investigated by using photoluminescence (PL) measurements. The PL spectra related to impurity level are dominated by the emission band at 1.355 eV. The temperature dependences of the PL intensity, peak energy, and full-width at half-maximum are characterized by the configuration coordinate model. The acceptor level located at about 0.45 eV above the valence band is detected by using Hall effect and deep-level transient spectroscopy measurements. This acceptor level is probably associated with the 1.355 eV emission band formed by P atoms.

Optical spectroscopy of titanium-doped CdZnTe

The energy level diagram of titanium in CdZnTe grown by the vertical Bridgman method has been investigated by using a variety of optical spectroscopy techniques: photoluminescence (PL), PL excitation (PLE) and deep level optical spectroscopy (DLOS). By PL spectroscopy, a broad emission band around 0.8 eV, with a double-peaked shape, is reported for the first time. PL and PLE results, combined with the DLOS data of the eV titanium-related electron trap lead us to (i) attribute the 0.8 eV emission band to the internal transition of the single donor and (ii) demonstrate that the state is split by the combined action of spin-orbit coupling and a strong dynamic Jahn-Teller effect. The double-peaked shape of the 0.8 eV emission band is interpreted as a combination of two recombination processes involving . A configuration coordinate diagram of ions is proposed. Finally the F centre has been identified in CdZnTe:Ti by PL; the threshold ionization energy of this centre is determined by PLE at 1.441 eV.

Temperature dependence of photoluminescence of layer semiconductor p-GaTe

The photoluminescence (PL) spectra of undoped p-GaTe at 97 K are dominated by two emission bands at 1.76 and 1.59 eV. For the 1.76 eV emission band, the behavior of the peak energy and full-width at half-maximum as a function of temperature shows the characteristics of the recombination mechanism for the free exciton. We find, from the temperature dependence of the PL intensity of the 1.59 eV emission band, that the band is caused by the transition from the donor level to the acceptor level located at 0.15 eV above the valence band.

Low temperature time resolved photoluminescence of the 3.1 and 4.2 eV emission bands in Ge-doped silica

Time resolved photoluminescence (PL) has been performed on Ge-doped silica preform in the temperature range 10 to 295 K. Under pulsed KrF laser (5 eV) the well known α and β emissions have been recorded at different delays from excitation. An accurate analysis of the time resolved spectra taken at different temperatures has shown the composite property of the two PL structures. At room temperature α components ( α 1, α 2) are peaked at 4.09 and 4.26 eV with a decay time of about 10 ns. The peak energies of β 1 and β 2 components are calculated at 3.03 and 3.21 eV with lifetimes of 111 and 94 μs, respectively. As temperature is decreased, α 1 and α 2 display the normal behaviour increasing in intensity down to 125 K; on the contrary, in the same temperature range, β 1 and β 2 undergo a quenching of their intensities. Taking into account their mutual spectral characteristics, α 1 has been correlated to β 1 and α 2 to β 2. The two sets of emission bands are tentatively attributed to a single center stabilized in different environments of the glassy matrix.

Defect luminescence in Li2O crystal under γ-ray irradiation

Luminescence emitted under γ-ray irradiation in Li2O single crystal has been measured at 77—298 K using a 60Co source for the first time. Effects of annealing temperature (773 or 1073 K) and cooling rate (about 50 or 400 K/h) were studied. The luminescence emission was observed at 5.5—2.5 eV. The luminescence spectrum at 298 K was found to consist of five emission bands. The peak energies, in eV, of the luminescent bands in Li2O annealed at 773 K and cooled with a quenching rate of 50 K/h are: 4.70, 4.13, 3.72, 3.30 and 2.87. It is suggested that the 4.70 eV emission band corresponds to the luminescence of a self-trapped exciton. The luminescence emissions at 3.72, 3.30 and 2.87 eV were assigned to the F0, F+ and F2 centers, respectively. The origin of the luminescence band at 4.13 eV could be related to intrinsic defect or impurity luminescence. The activation energy for the thermal excitation into a non-radiative decay channel was elucidated to be 380, 140 and 115 meV for the 4.70, 4.13 and 3.72 eV bands, respectively. The emission yield of F+ centers was strongly affected by the condition of heat treatment before irradiation.

Role of zinc in the optical properties of vanadium-doped CdZnTe

High-resistivity vanadium-doped CdTe and CdZnTe crystals were investigated by photoluminescence in the near-infrared spectral range. The observed shift of the near band edge luminescence with respect to the sample position along the ingot is explained in terms of a non-uniform distribution of zinc. Two deep luminescence bands were detected at around 0.8 eV and 1 eV. The electron - phonon interaction strengths (Huang - Rhys parameter S) of the two related centres have been estimated and a configuration coordinate diagrams proposed. The 0.8 eV emission band is assigned to the electrically active eV centre. The double peaked shape of the 0.8 eV emission band is a result of either an overlap between two emissions bands or the Jahn - Teller effect including a small quadratic effect. In the framework of the first hypothesis, the emission band is interpreted as a combination of two simultaneous recombination processes: the internal transition and the conduction band level transition.

Electron beam induced structural changes in Bi 2 Sr 2 CaCu 2 O 8+x studied by cathodoluminescence microscopy and secondary electron emission

Sr2CaCu2O8+x superconducting ceramics have been irradiated in the scanning electron microscope (SEM), and the irradiation-induced effects investigated by cathodoluminescence (CL), secondary electron emission (SEE) and X-ray microanalysis. Electron beam irradiation causes a slight Bi depletion and an inhomogeneous Ca distribution. A higher CL intensity emission is found in the irradiated areas, where besides an enhancement of the oxygen content related 2. 4 eV band, another CL bands probably related to new non-superconducting phases induced by irradiation can be observed. SEE yield measurements allow to detect an oxygen depleted region surrounding the irradiated areas. X-ray microanalysis shows that this intermediate region retains the cationic composition of the unaffected material. CL spectra from bright zones inside the same area also show a dominant 2. 4 eV emission band, which supports its relation with oxygen deficiency or rearrangement in high-\(\) superconductors.