Showing papers on "Photoluminescence published in 1970"

Germanium‐Doped Gallium Arsenide

Abstract: Germanium‐doped GaAs crystals were grown on GaAs seeds from Ga solution. The properties of the Ge‐doped GaAs layers were examined by Hall effect measurements from 20° to 400°K and by photoluminescence measurements between 12° and 300°K. It was found that Ge‐doped GaAs is always p‐type when grown at 900°–875°C from Ga solution containing 56 at.% or less Ge. The temperature dependence of the Hall coefficient and the photoluminescence experiment indicated an acceptor energy level of 0.035 and 0.038 eV respectively. It was also found that at least 85% of the Ge was present as an acceptor in the GaAs crystals when the growth solution contained two atom percent or less Ge.

Acceptor Luminescence in High-Purity n -Type GaAs

Abstract: Photoluminescence of epitaxial GaAs in a magnetic field has established the origin of several recombination transitions 20 to 40 meV off the band edge. The data indicate that two acceptor levels are present in high purity material and that two free-electron-neutral-acceptor and two donor-acceptor pair bands are observed in photoluminescence at low temperatures.

Optical Absorption and Luminescence of Excitons is Silver Halides Containing Isoelectronic Impurities. : Part II. AgBr:Cl^- and AgBr

Abstract: Low temperature optical spectra are studied on AgBr:Cl - in comparison with AgBr. Contrary to AgBr:I - , no bound excitons at chlorine are formed in AgBr:Cl - . Absorption spectra of AgBr:Cl - are similar to AgBr, except for existence of exciton absorption without phonon assistance. Photoluminescence spectra of AgBr and AgBr:Cl - contain emission band due to decay of free exciton. This observation leads one to conclude that positive holes in AgBr are not self-trapped even at 2°K. Comparison of free exciton transition energies between absorption and emission spectra reveals existence of two kinds of phonons assisting the indirect transition. Various extrinsic emission bands are also observed. One of them corresponds to shallow-bound exciton at Cd 2+ -type impurity and the other to deep-bound exciton at residual iodine. Transition energies of free and bound excitons, except iodine-bound exciton, shift to higher energy in proportion to chlorine concentration. These results can be explained by virtual crystal...

PHOTOLUMINESCENCE IN Bi12SiO20 AND Bi12GeO20

Abstract: A red photoluminescence emission band peaking at 1.95 eV is reported for Bi12SiO20 and Bi12GeO20. The mechanism for exciting the luminescence transition is considered, and a tentative model for the luminescence center is proposed. It is suggested that the most likely mode of excitation involves resonance transfer of energy from excitons to the luminescence center by means of a radiationless process followed by subsequent light emission from the luminescence center.

Optical properties of the europium chalcogenides

Abstract: The measured optical properties of the Eu chalcogenides are surveyed in an attempt to determine those aspects of the electronic structure of these materials that have been established. Optical absorption as well as optical and magneto-optical reflectivity data are discussed, along with the results of photoconductivity, photoluminescence and photoemission measurements and of magnetooptical measurements in the vicinity of the absorption edge. It is concluded that the fundamental absorption edge is due to the onset of Eu++ 4f to 5d transitions of the type 4f7(8S7/2)→ 4f6(7FJ)5d(T2g) and that a higher energy reflectivity peak is primarily dtuoe 4f7(8S7/2) →4f6(7FJ)5d(Eg) transitions, although anion p-valence band to Eu conduction band transitions may also be involved. The principal unanswered questions involve the relative positions of the Eu 6s and 5d(T2g) states, the breadth of the 5d levels and the role played by exciton effects in the 4f to 5d optical transitions.

Photoluminescent Saturation in GaP (Zn, O)

Abstract: This paper describes a room‐temperature study of the red emission from GaP (Zn, O) as a function of 4880‐ and 5145‐A photoexcitation intensity, and was initiated to determine the importance of nonradiative bulk recombination centers shunting the radiative path through the Zn–O complexes. The technique used is the investigation of the saturation behavior of the emitted red light as a function of excitation intensity. An analysis is given in which the functional dependence of the red‐light emission on such parameters as the excitation absorption coefficient, diffusion length, surface recombination velocity, and excitation beam diameter is considered. The diffusion lengths and surface recombination velocities were obtained by means of low‐intensity excitation spectral measurements. Diffusion lengths covering the range 0.5–5.0 μ were measured and surface recombination veloclties from 5 to 100 times the diffusion velocity were extracted. The samples saturated at intensities ranging from 3×1019 photons/sec cm2 ...

CdSnP2 EMISSION AND DETECTION OF NEAR‐INFRARED RADIATION

Abstract: The spectral dependence of the photoluminescence and the time decay of the cathodoluminescence are reported for CdSnP2 single crystals for 1.7

dc Electroluminescence and Related Properties in Evaporated Thin Films of ZnS(Cu, Mn, Cl)

Abstract: Properties of dc electroluminescence(EL) are studied for two groups of films, one evaporated at rather low temperatures (below 230°C, denoted as film-L) and the other at high temperatures (above 230°C, also denoted as film-H). In sandwich cell, stable EL emission is obtained when the counter electrode is negative for film-L, and positive for film-H. Photovoltage appears with the opposite sign for the film-L and film-H. From the observation of photoluminescence (PL) and EL for the sandwich cell and two types of gap cell (underlying and overlying electrode types), the relations between activator distribution and EL emission are obtained. The emitting portions are found different for the gap cell between the film-L and film-H by microscopic observation. Hole injection mechanism is proved to be predominant in both groups. The same experiments are made for the films doped with activators by "Embedding method."

ion implantation of bismuth into GaP. I. photoluminescence

Abstract: Photoluminescence from the bismuth isoelectronic trap implanted into GaP is investigated for various ion doses and annealing conditions. A thin coating of silicon oxide is found to be essential to prevent thermal decomposition of the implanted surface during annealing. In isochronal anneal studies the intensity of the Bi luminescence increases rapidly between 650 and 800°C. For 200 keV implants, the dose for maximum luminescence is ∼3.5 × 1012 ions/cm2, corresponding to an average concentration of ∼1018/cm3. However, for the optimum dose and anneal, one observes only ∼10 per cent of the light intensity expected from the estimated number of substitutional ions, and the emitting ions are situated in lattice sites with strong local strain. This strain is evident in the photoluminescence spectrum by the appearance of a strong no-phonon line which results from an otherwise forbidden transition when strain or an external field are present. The luminescence data are correlated with channeling experiment...

Photoluminescence of ZnS : TbF3 Thin Films

Abstract: Photoluminescence from evaporated films of approximately 1µ thick has been studied at room temperature as a function of the fluoride concentration. The excitation or pumping wavelength varies from 4880 to 2600Aa, while the Tb3+ emission transition at 5425Aa is monitored at the output. For pumping photon energies below the forbidden gap, the excitation spectra resemble that of the pure film or single crystal. For this case, the conversion efficiency with 4880Aa pumping in samples that contain 0.86% is close to 100% as compared to 0.8% for pure . With pumping energies above the gap, photoluminescence presumably due to energy transfer from electron‐hole pairs has also been observed; however, such a process yields conversion efficiency generally in the 10−5–10−6 range. These results support the model that electroluminescence in devices using similar films arises from direct excitation of Tb3+ levels by hot electrons as proposed by one of the authors.

Quenched-in Photoluminescent Color Centers in NaI

Abstract: Crystals of NaI, KI, and KCl have been quenched from temperatures as high as 450 °C by rapid immersion in liquid nitrogen. In the case of NaI, very strong absorption bands at 255 nm (Q1) and 226 nm (Q2) may be produced by quenching the crystal from about 360 °C. The excitation spectrum for a characteristic luminescence at 375 nm, is identical, within the limits of experimental accuracy, with bands produced by stoichiometric excess iodine. Similar results were obtained for quenched KI, although the luminescent quantum efficiency was smaller. Negative results were obtained for quenched KCl. Analysis of the observed properties leads to the conclusion that the defect responsible for the 375 nm luminescence is, or is related to, the single cation vacancy. NaJ-, KJ- und KCl-Kristalle werden von Temperaturen bis zu 450 °C durch schnelles Eintauchen in flussigen Stickstoff abgeschreckt. Fur NaJ konnten starke Absorptionsbanden bei 255 nm (Q1) und 226 nm (Q2) durch Abschrecken des Kristalls von etwa 360 °C erhalten werden. Das Anregungsspektrum fur eine charakteristische Lumineszenz bei 375 nm ist innerhalb der Fehlergrenzen identisch mit Banden, die durch stochiometrisch uberschussiges Jod verursacht werden. Ahnliche Ergebnisse wurden fur abgeschrecktes KJ erhalten, obgleich die Quantenausbeute der Lumineszenz kleiner war. Negative Ergebnisse wurden fur abgeschrecktes KCl erhalten. Eine Analyse der beobachteten Eigenschaften fuhrte zu der Annahme, das die fur die 375 nm-Lumineszenz verantwortlichen Defekte isolierte Kationenlucken sind oder mit diesen zusammenhangen.

Photoluminescence Study of the Interface between GaAs Epitaxial Layer and its Substrate

Abstract: Photoluminescence measurements are used to study the cause of abnormal interface phenomena, such as non-ohmic behavior or a dip in the carrier concentration profile observed at the interface between a GaAs vapor epitaxial layer and its substrate From measurements taken on epitaxial crystals grown at different conditions, the emission band which was supposed to be caused by copper impurities are observed at the interface Therefore these abnormal interface phenomena are probably associated with copper impurities

Photoluminescence of Cr-Doped CaTi O 3

Abstract: At 4 and 77 K, photoluminescence from nominally undoped and 0.0025% Cr-doped CaTi${\mathrm{O}}_{3}$ shows identical spectra in the infrared with an intensity ratio of 1:2. The emission is attributed to the $^{2}E\ensuremath{\rightarrow}^{4}A_{2}$ transition of the ${\mathrm{Cr}}^{3+}$ ion at a ${\mathrm{Ti}}^{4+}$ site. At 4 K it consists of a single no-phonon line at 1.744 eV of half-width 1.5 meV and a complex vibronic spectrum which is anomalously intense. Data at 77 K show a 2-meV splitting of the $^{2}E$ state. The absorption spectrum of CaTi${\mathrm{O}}_{3}$:Cr is dominated by a "background absorption" by unknown defects. From the coincidence of the excitation spectrum with the absorption spectrum, we conclude that the excitation is dominated by absorption by these unknown defects which transfer energy into ${\mathrm{Cr}}^{3+}$. In undoped CaTi${\mathrm{O}}_{3}$ a single-exponential decay of the emission is reported, with decay time 700 \ensuremath{\mu}sec. In CaTi${\mathrm{O}}_{3}$:0.0025% Cr, on the other hand, two exponentials with decay times 700 \ensuremath{\mu}sec and 11 msec were observed. The former is assigned to ${\mathrm{Cr}}^{3+}$, the latter to the time of energy transfer from defects responsible for the background absorption to the ${\mathrm{Cr}}^{3+}$. We also report a visible emission consisting of a broad structureless band centered at 2.7 eV, with half-width 0.7 eV. Presumably, it is recombination radiation caused by the recombination of a free charge carrier with a trapped charge at an unknown defect. Its excitation spectrum gives a band gap for CaTi${\mathrm{O}}_{3}$ of 3.70 eV at 4 K.

Photoluminescence of EuSe and the magnetic polaron model

Abstract: We report on extensive new measurements relating to the near-infrared photoluminescence of EuSe first reported by Busch and Wachter in 1966. The emission and excitation spectra are obtained as functions of temperature and external magnetic field. The total red shift is 0.13 eV in the excitation spectrum (in good agreement with the absorption-edge shift), and 0.25 eV in the emission spectrum. At 4.3°K an external magnetic field of 11 kOe quenches the yield to about 30% of its field-free value. The experimental results are discussed in relation to photoconductivity and optical absorption measurements. An intrinsic and localized model for the luminescence is proposed, in which the emission takes place by radiative recombination of a localized magnetic polaron with a hole in the europium 4f-shell.

Some Optical Properties of Cadmium Sulfide Containing Phosphorus and Arsenic

Abstract: Ion implantation and sputtering have generated renewed interest in the possibility of obtaining p‐type CdS. However, little is known concerning the properties of acceptors. In an attempt to learn something about acceptors in CdS, phosphorus‐ and arsenic‐doped samples have been prepared by diffusion in a saturated Cd atmosphere at 800°C for 24 h. The electrical and optical properties of the doped samples are compared with undoped test samples (fired in saturated Cd atmosphere but without added dopant). The electrical properties indicate only a slight compensation due to the presence of P and As. The optical studies (photoluminescence, photoconductivity, and optical absorption) yield a level about 1‐eV above the valence band, which is presumably the binding energy of an electron to a compensated P or As acceptor.