Effect of iodine doping on the luminescent properties of the photochromic material CdBr<Subscript>2</Subscript>:Cu<Superscript>+</Superscript>

The effect of iodine doping on the roentgenoluminescence (RL) and thermoluminescence (TL) of CdBr₂:Cu⁺ is studied using CdBr₂:(Cu⁺ ,I^-) crystals grown by the Bridgman-Stockbarger method from melts containing 0.5 wt % CuBr and 0.15, 0.5, or 5.0 wt % CdI₂. The results demonstrate that, with increasing iodine content, the RL intensity first rises and then drops; in addition, the RL band shifts from 560 to 490–510 nm. At low CdI₂ levels, the TL curve shows peaks at 110, 130, 152, and 168 K, characteristic of CdBr₂:Cu⁺. At the maximum iodine concentration, the TL curve shows a weak peak at 115 K. The TL spectrum of lightly iodine-doped crystals is dominated by the 490-nm emission, which is attributable to heteronuclear anion excitons. The formation of nI^- clusters in heavily doped CdBr₂:(Cu⁺,I^-) crystals reduces the concentration of (BrI)^- hetero-nuclear centers. The nature of the trapping levels responsible for the TL of the crystals is discussed.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 235–239.Original Russian Text Copyright © 2005 by S. Novosad, I. Novosad, Borodchuk.     

Luminescent properties of Pb<Superscript>2+</Superscript>- and Mn<Superscript>2+</Superscript>-activated CdI<Subscript>2</Subscript> crystals

The luminescent properties of CdI₂, CdI₂:Pb²⁺, CdI₂:Mn²⁺, and CdI₂:Pb²⁺,Mn²⁺) crystals have been studied at temperatures from 85 to 295 K under optical and x-ray excitation. Analysis of new and earlier spectroscopic data suggests that the 560-nm luminescence of CdI₂:Pb²⁺ and CdI₂:(Pb²⁺,Mn²⁺) crystals under excitation on the long-wavelength component of the A absorption band of Pb²⁺ centers is due to Pb²⁺-bound anion excitons. The 640-to 660-nm emission of these crystals is attributable to α centers. The manganese luminescence in the codoped material originates from both intracenter Mn²⁺ excitations and a sensitized process due to energy transfer from the host and Pb²⁺-related centers. The mechanisms of recombination and energy transfer processes in cadmium iodide crystals codoped with Pb²⁺ and Mn²⁺ are discussed.     

Recombination luminescence of activated CaI<Subscript>2</Subscript> crystals

Data are presented on the recombination luminescence of CaI₂:Eu²⁺, CaI₂:Gd²⁺, CaI₂:Tl⁺, CaI₂:Pb²⁺, and CaI₂:Mn²⁺ crystals grown by the Bridgman-Stockbarger method. It follows from their photostimulated luminescence, roentgenoluminescence, and thermostimulated luminescence spectra that the activation of CaI₂ with Gd²⁺, Eu²⁺, Tl⁺, Pb²⁺, and Mn²⁺ cations, which produce anion defects, leads to the formation of defect complexes which act as electron traps and determine the 90-K photostimulation spectra of the crystals. The observed effect of the nature of the dopant on the photostimulation spectrum indicates that the doped calcium iodide crystals contain near-activator F- and F _A -type electron centers. Under x-ray and optical excitation, the trapping levels in the crystals are filled mainly by charge carriers delocalized from hydrogen- and oxygen-containing centers. The activation increases the decay probability of impurity-bound excitons.     

Recombination luminescence of CaI<Subscript>2</Subscript> crystals activated with Eu<Superscript>2+</Superscript>, Gd<Superscript>2+</Superscript>, Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, and Mn<Superscript>2+</Superscript>

The spectral characteristics of thermostimulated luminescence, steady-state roentgenoluminescence and photostimulated luminescence (PSL) buildup and decay kinetics, and the effect of IR irradiation on the roentgenoluminescence yield and glow curves of CaI₂:Eu²⁺, CaI₂:Gd²⁺, CaI₂:Tl⁺, CaI₂:Pb²⁺, CaI₂:Mn²⁺, and CaI₂: Pb²⁺, Mn²⁺ crystals grown by the Bridgman-Stockbarger method have been studied in the temperature range 90–295 K. Coupled with earlier data, the present results on the influence of oxygen and hydrogen impurities on the spectral characteristics of CaI₂ indicate that the activation of calcium iodide with Eu²⁺, Gd²⁺, Tl⁺, Pb²⁺, and Mn²⁺ leads to the formation of cation impurity-native defect complexes, which act as carrier traps and are responsible for the thermostimulated luminescence in the range 150–295 K. IR exposure after 90-K x-ray excitation gives rise to flash PSL and influences the thermostimulated luminescence light sum. The nature of the emission and trapping centers involved and the mechanisms of recombination luminescence excitation in the crystals are discussed.     

Preparation and properties of orthorhombic TlInS<Subscript>2</Subscript>

A procedure is described for crystal growth of orthorhombic TlInS₂. The lattice parameters of the grown crystals are a = 6.88 Å, b = 14.04 Å, and c = 4.02 Å (sp. gr. P222₁, Z = 4, _x = 6.59 g/cm³). The dielectric permittivity of the crystals is measured from 170 to 300 K. The spectral dependence of the 300-K photocurrent through the crystals indicates that orthorhombic TlInS₂ is a wide-gap semiconductor. Its band gap, E _g = 2.52 ± 0.01 eV, slightly exceeds that of monoclinic TlInS₂.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 138–142.Original Russian Text Copyright © 2005 by Nadjafov, Alekperov, Guseinov.     

Novel single-host Al<Subscript>1−x</Subscript>Si<Subscript>x</Subscript>C<Subscript>x</Subscript>N<Subscript>1−x</Subscript>: Mn<Superscript>2+</Superscript> white phosphors for field emission displays

A white-emitting novel Al_1?x Si _x C _x N_1?x : Mn²⁺ carbidonitride phosphor was synthesized by introducing SiC into AlN: Mn²⁺at the temperature as low as 1500?°C. The influence of Mn²⁺ and SiC doping concentration on the structure, morphology and luminescent properties was systematically investigated by XRD, EDS, solid state NMR, FESEM, and PL. The relatively low calcination temperature endows AlN: Mn²⁺ with different luminescent properties. Under 254 nm UV excitation, it not only exhibits a characteristic red emission from Mn²⁺ but also covers a broad violet-blue-green emission from defects. The CIE coordinates (0.2999, 0.2510) precisely locate in the white region. With the introduction of SiC, an increasing of the red emission from Mn²⁺ is observed, while no variation occurs for the defect emission. The maximum red luminescence is attained for the composition of x?=?0.05 that has an improved thermal stability by 20%. Finally, a low-voltage FED device was fabricated by using Al_0.95Si_0.05C_0.05N_0.95: 0.7% Mn²⁺ carbidonitride phosphor. Under low-voltage excitation, it exhibits a high brightness, low saturation, and good color stability, which makes Al_1?xSi_xC_xN_1?x: Mn²⁺ carbidonitride phosphor have a great potential for full color FEDs.     

A new red-emitting Ce, Mn-doped barium lithium silicate phosphor for NUV LED application

A series of new red-emitting Ce³⁺, Mn²⁺-doped barium lithium silicate phosphors, with general formula Ba₂Li₂Si₂O₇: Ce³⁺, Mn²⁺, were synthesized by solid-state reactions. The Mn²⁺ in this system can be effectively excited in a wide UV region especially in the NUV range, and has broad red emission after NUV excitation through Ce³⁺-Mn²⁺ energy transfer, as well as excellent thermal stability. The blue-shift behavior of Mn²⁺ emission with increasing temperature can be described in terms of the phonon-electron interaction. The promising luminescence properties make it a red candidate for application in NUV chip pumped LED.     

Regular Arrays of (Zn,Mn)S Quantum Wires with Well-Defined Diameters in the Nanometer Range

Zn_1–x Mn _x S, with x varying between 0.01 and 0.30, were formed inside the ordered pore systems of different mesoporous SiO₂ matrices. Because of the highly ordered structure of the hosts, regular arrays of Zn_1–x Mn _x S quantum wires with lateral dimensions of 3 and 5.5 nm, respectively, separated by 2-nm SiO₂ barriers were obtained. The wires were characterized using photoluminescence (PL) and PL excitation (PLE) spectroscopy at liquid Helium temperatures. The PL of the wires is dominated by the ⁴T₁ ⁶A₁ internal transition of the Mn²⁺(3d⁵) ions. The corresponding PLE spectra show higher internal Mn transitions as well as the band to band transition. The energies of the internal Mn transitions are typical for Mn²⁺ on a cation site of (II,Mn)VI semiconductors. Because of the comparable bandgaps of the SiO₂ and the Zn_1–x Mn_xS as well as the small exciton Bohr radius in (Zn,Mn)S quantum confinement effects in the wires are less than about 150 meV.     

Spectroscopy of Yb3+ in Cubic ZrO2 Crystals

The absorption and luminescence spectra of Yb³⁺ ions in yttria-stabilized zirconia crystals are studied. The site-selective luminescence spectra of a ZrO₂–12 mol % Y₂O₃–0.3 mol % Yb₂O₃ crystal are obtained under excitation at different wavelengths within the absorption band. For this crystal, Yb³⁺ luminescence spectra are also measured with 3-ms and 5-s delays relative to the excitation pulse. The results are interpreted under the assumption that the crystals contain three distinct types of optical centers.     

Effect of Bi Doping on the Optical Properties of CdI<Subscript>2</Subscript>

The effect of Bi impurity on the optical absorption and roentgeno-, photo-, and thermoluminescence spectra of CdI₂ crystals grown by the Bridgman-Stockbarger method is studied. CdI₂ activation with BiI₃ produces a number of absorption bands related to electronic transitions of Bi³⁺. Bi produces no emission centers in CdI₂. The 550- to 560-nm luminescence of CdI₂ is due to the radiative recombination of self-trapped anion excitons. The observed changes in spectral distribution and the reduction in light yield upon CdI₂ activation with Bi³⁺ are mainly due to the reabsorption of emission from native centers by activator centers. Under x-ray excitation, CdI₂: Bi³⁺ accumulates a small light sum at shallow trap levels related to native defects.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 886–891.Original Russian Text Copyright © 2005 by Kravchuk, Novosad, Voitsekhovskaya.     

Optical and photoelectric properties of Cd<Subscript>1 - <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>x</Subscript>As<Subscript>2</Subscript> single crystals

The optical absorption, photoconductivity, and short-circuit photocurrent spectra of structurally perfect Cd_{1 - x} Zn_xAs₂ (x = 0.03, 0.05, 0.06) single crystals are studied for the first time near the intrinsic edge in the range 80–300 K. The results demonstrate that the intrinsic edge in the solid solutions is due to indirect transitions involving the formation of excitons for both the E c and E c polarizations. The indirect gaps _g ⁱ of the solid solutions are determined. In the range 80–300 K, the data for x = 0–0.06 and both polarizations are well fitted by _g ⁱ (x) = _g ⁱ (0) + 0.0866x + 2.35x ². The introduction of 6 mol % ZnAs₂ into CdAs₂ increases its _g ⁱ by 14 meV.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 268–272.Original Russian Text Copyright © 2005 by Morozova, Marenkin, Mikhailov, Koshelev.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

GeO2 dopant induced enhancement of red emission in CaAl12O19:Mn phosphor

In order to search efficient red-emitting phosphors for white LEDs application, CaAl₁₂O₁₉:Mn⁴⁺ phosphors have been prepared by a combustion method assisted with GeO₂ flux. The influence of GeO₂ concentration and annealing temperature on the structure and luminescence intensity for the phosphors has been investigated. The mechanism for luminescence enhancement has been discussed. At GeO₂ doping concentration of 1.5 mol%, the red emission intensity increases by 81% under 330 nm UVA excitation. More isolated luminescence center Mn⁴⁺ ions rather than pairs of Mn⁴⁺-Mn²⁺ ions are formed in the lattice with the introduction of GeO₂ at high temperature oxidation, leading to the enhancement of the red emission. A feasible new way to enhance the red emission in CaAl₁₂O₁₉:Mn⁴⁺ phosphor is obtained.     

Synthesis and photoluminescence spectroscopy of BaGeF6:Mn4+ red phosphor

We synthesized Mn⁴⁺-activated BaGeF₆ red phosphor by the chemical reaction method from HF, H₂SiF₆, BaF₂, KMnO₄, and GeO₂ powder. The structural and optical properties of BaGeF₆:Mn⁴⁺ were investigated using X-ray diffraction analysis, secondary electron microscopy observation, electron spin resonance measurement, photoluminescence (PL), PL excitation (PLE) and Raman scattering spectroscopies, and luminescence decay time measurement. Temperature dependence of the PL intensity was measured from T = 20 to 500 K and analyzed by taking into consideration the Bose–Einstein phonon occupation number. The PLE spectra measured at T = 20 and 300 K and luminescence decay time at T = 20–460 K were also analyzed based on the Franck–Condon and conventional thermal quenching models, respectively. Comprehensive discussion was given on the Mn⁴⁺-related PL properties and Raman scattering behaviors in a family of the barium hexafluorometallate phosphors.     

Gel Growth, Luminescence, and Scintillation of PbSO4 Crystals

PbSO₄ powders and crystals are prepared using gel growth, and their chemical and phase compositions are determined. The luminescence spectra of the crystals are measured between 10 and 300 K under excitation with 5- to 40-eV synchrotron radiation, the excitation spectra of the UV and blue emission bands are obtained, and the temperature effect on the emission decay is examined. The luminescence spectra show bands at 340 and 380 nm, which experience strong thermal quenching and arise from different emission centers. Increasing the temperature from 10 to 300 K accelerates the luminescence decay by three orders of magnitude, bringing it to the nanosecond range. Under gamma excitation in the range 122–1332 eV, the average room-temperature light output of the PbSO₄ crystals exceeds that of Bi₄Ge₃O₁₂ by 20%, with emission decay times ₁ = 1.85 ns, ₂ = 14.5 ns, and ₃ = 125–150 ns.     

Effect of BiI<Subscript>3</Subscript> doping on the optical properties of CaI<Subscript>2</Subscript>

The effect of BiI₃ doping on the optical absorption spectra and roentgeno-, photo-, and thermoluminescence of CaI₂ scintillator crystals has been studied in the temperature range 90–295 K. The crystals were grown by the Bridgman-Stockbarger method. Doping of CaI₂ with BiI₃ from the melt gives rise to absorption bands centered at 466, 400, and 350 nm, which can be interpreted as the A, B, and C bands due to electronic transitions from the ¹ S ₀ state to the ³ P ₁, ³ P ₂, and ¹ P ₁ levels of a free Bi³⁺ ion. The absorption band at 270–290 nm is assignable to near-activator excitons. Changes in spectral composition and the reduction in luminescence intensity caused by Bi³⁺ doping of CaI₂ are associated mainly with the reabsorption of the emission from centers characteristic of the host by activator centers. Under x-ray excitation, the spectrum of heavily doped crystals shows, in addition, a weak emission centered around 620 nm, which is probably due to an impurity phase. The light sum of CaI₂:Bi³⁺ under x-ray excitation is small and is due to shallow traps. Upon Bi³⁺ substitution on the cation site of CaI₂, the excess charge of the activator is probably compensated by unintentional O^2? impurity and vacancy pairs near Bi³⁺ centers—one vacancy in a neighboring cation site and the other in a neighboring anion site.     

Three oxidation states and atomic-scale <Emphasis Type="Italic">p–n</Emphasis> junctions in manganese perovskite oxide from hydrothermal systems

Perovskite oxides have provided magical structural models for superconducting and colossal magnetoresistance, and the search for nano-scale and/or atomic-scale devices with particular property by specific preparations in the same systems has been extensively conducted. We present here the three oxidation states of manganese (Mn³⁺, Mn⁴⁺, Mn⁵⁺) in the perovskite oxide, La_0.66Ca_0.29K_0.05MnO₃, which most interestingly shows the rectifying effect as atomic-scale p–n junctions (namely FY-Junctions) of single crystals and films. The family of cubic perovskite oxides were synthesised by the so-called hydrothermal disproportionation reaction of MnO₂ under the condition of strong alkali media. The new concept of the atomic-scale p–n junctions, based on the ideal rectification characteristic of the p–n junctions in the single crystal, basically originates from the structural linkages of [Mn³⁺–O–Mn⁴⁺–O–Mn⁵⁺], where Mn³⁺ and Mn⁵⁺ in octahedral symmetry serve as a donor and an acceptor, respectively, corresponding to the localized Mn⁴⁺ .     

Structural and optical study of GaMnAs/GaAs

GaMnAs/GaAs was obtained with mass-analyzed low energy dual ion beam depostion technique with Mn ion energy of 1000 eV and a dose of 1.5 × 10¹⁸ Mn⁺/cm² at the substrate temperature of 400°C and was annealed at 840°C. X-ray diffraction spectra showed that Ga_5.2Mn, Ga₅Mn₈, -Mn and Mn₃Ga were obtained in the as-grown sample. After annealing Mn₃Ga and -Mn disappeared, Ga₅Mn₈ tended to disappear, Ga_5.2Mn crystallized better and new phase of Mn₂As was generated. The photoluminescence spectra of the as-grown sample showed that the 1.5042 eV GaAs exciton peak, 1.4875 eV peak involving a carbon acceptor and a broad band near 1.35 eV. After annealing at 840°C, the 1.5042 eV peak and 1.4875 eV shifted to 1.5065 and 1.4894 eV, respectively, and the photoluminescence intensity of the 1.35 eV band increased greatly.     

Thermodynamic Properties of Lanthanum Chlorides

The enthalpies of atomization of LaCl, LaCl₂, and LaCl₃ are determined by measuring the vapor pressure over liquid and solid LaCl₃ and assessing the equilibrium constants of the gas-phase reactions BaCl + La = Ba + LaCl and 2BaCl + La = 2Ba + LaCl₂, using the appearance potentials of ions and the ionization potentials of the lanthanum chlorides: _at H ⁰(LaCl, 298 K) = 502.4 ± 0.5 kJ/mol, _at H ⁰(LaCl₂, 298 K) = 999.2 ± 0.8 kJ/mol, and _at H ⁰(LaCl₃, 298 K) = 1524.6 ± 2.0 kJ/mol. In addition, the enthalpies of formation of gaseous lanthanum chlorides are determined using new data on the thermodynamic functions of condensed LaCl₃ and gaseous LaCl, LaCl₂, and LaCl₃: _f H ⁰(LaCl, g, 298 K) = 48.9 ± 1.0 kJ/mol, _f H ⁰(LaCl₂, g, 298 K) = –326.6 ± 1.2 kJ/mol, and _f H ⁰(LaCl₃, g, 298 K) = –730.7 ± 2.0 kJ/mol. The ionization and appearance potentials of ions resulting from electron impact ionization of LaCl₃ are determined.     

Electrical conductivity study of oxidation process in manganese-substituted magnetites

During oxidation in air of finely-grained manganese-substituted magnetites (Mn _0.8x ²⁺ Fe _1–0.8x ³⁺ )_A– (Fe _1+0.6x ³⁺ Fe _1–0.8x ²⁺ Mn _0.2x ³⁺ )_BO ₄ ^2– (A=tetrahedral, B=octahedral) the temperature dependence of the electrical conductivity over a temperature range of 100 to 700° C was investigated. Below 500° C the evolution of electrical conductivity might be closely associated with the position and nature of cations in the spinel lattice. The profile of the =f(t) curves show that the mechanism of electrical conduction in the temperature range 150 to 300° C can be explained in terms of the oxidation of Fe²⁺ to Fe³⁺ ions at octahedral sites. For the temperature range 300 to 400° C the conductivity involves the hopping of electrons from tetrahedral-site Mn²⁺ ions to tetrahedral-site Mn³⁺ ions. Above 500° C the oxidation of Mn²⁺ ions leads to an increase in conductivity with the generation of new phases of -Fe₂O₃, Mn₂O₃ and -(MnFe)₂O₃.