A study of complex glow curves of Quenched NaCl:Ca crystals

Glow curves of the thermally pretreated NaCl:Ca crystals are recorded and are found to be complex in nature. The complex glow curve is analysed using thermal cleaning technique and the trap parameters are calculated by various methods. The glow peaks have been tentatively attributed to impurity and various types of colour centers.     

State of dispersion of impurity on formation of Z1-centres in NaCl:Sr2+ crystals

Thermoluminescence (TL) and Optical absorption studies are carried out to study the bleaching kinetics of F-centre and formation of Z₁-centres in X-irradiated strontium doped NaCl crystals, both in as-grown state and in quenched state. An additional TL peak is observed in this crystal system after F-bleaching of irradiated samples which is attributed to thermal annealing of Z₁-centres. Various models proposed for Z₁-centres are reviewed in the light of these results and it is concluded that Z₁-centres are associated with impurity-vacancy dipoles.     

A Study of precipitation morphology in NaCl:Sr and NaCl:Ba crystals

Single crystals of sodium chloride grown from melt containing different concentrations of strontium and barium have been observed to contain a second phase precipitating throughout the interior in the form of thin rods and well defined polygonal platelets. Two types of rods have been observed, one type oriented along 〈100〉 and the other along 〈110〉 directions. The platelets are variously in the form of hexagons, octagons, and rhombs. The precipitates disappear on quenching the crystal and reappear on aging the crystals under suitable conditions.     

Mechanical characteristics of the NaCl: Eu2+ crystal system

Yield strength of NaCl: Eu²⁺ monocrystals was studied as function of both the dopant concentration and the annealing parameters. Main attention was paid to the strengthening mechanisms induced by the presence of europium related second phases the structure of which was controlled by means of optical methods. Depending on the nature of the second phases and their crystallographic relations with the matrix, two strengthening phenomena have been evidenced: this related with the presence of penetrable and that related with inprenetrable second phase particles. As far as the former ones can be sheared along with the matrix, the later — are overcomed due to a looping mechanism resembling the behaviour of metal alloys with the fcc — type of structure.     

Influence of Zn2+ ions concentration on the optical properties of Zn/Er:LiNbO3 crystals

Congruent Er³⁺(3 mol%):LiNbO₃ crystals codoped with ZnO (X mol %, X=0, 3, 6 and 7) were grown by the Czochralski technique. The Er contents in the crystals were measured by an inductively coupled plasma atomic emission spectrometer (ICP‐AES). Under 800 nm excitation, the upconversion emission spectra reveal an enhancement of the green emission with respect to the red emission when the Zn²⁺ ions are introduced into Er:LiNbO₃ crystal. The effect of Zn²⁺ ions concentration on the intensity ratio of the green to red emission has been investigated. Two cross‐relaxation processes (²H_11/2 + ⁴I_13/2 → ⁴I_11/2 + ⁴F_9/2 and ⁴F_7/2 + ⁴I_11/2 → ⁴F_9/2 + ⁴F_9/2) are involved in populating the ⁴F_9/2 state, which bypass the green‐emitting states. The OH^‐ absorption spectra indicate that the Zn²⁺ codoping leads to a decreased concentration of Er³⁺ cluster sites contributing to the enhancement of the green emission. The studies on UV‐vis absorption spectra show that the heavily codoped with Zn²⁺ results in the reformation of the Er³⁺ cluster sites in Er:LiNbO₃. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Glow curves and the emission of BaFCl:Eu2+

Thermoluminescence and the emission of γ-irradiated BaFCl:Eu²⁺ has been studied. A well defined glow peak at 400 K and a shoulder at 480 K are obtained in addition to those obtained as in undoped BaFCl. Thermoluminescence emission has shown a band at about 390 ∼ 400 nm. Additional glow peaks have been attributed to the luminescence centers as caused by europium impurity.     

Sr2+对GdVO4晶体生长和拉曼性能的影响

本文报道了Sr2+离子掺杂对GdVO4晶体生长和拉曼性能的影响.SrxGd1-xVO4晶体粉末经X射线粉末衍射分析,其结果仍属四方晶系,具有锆英石结构.实验表明,高掺杂浓度时,Sr2+离子不易取代Gd3+离子进入GdVO4晶体的晶格,易导致SrxGd1-xVO4晶体开裂和产生包裹体.XPS实验证明,SrxGd1-xVO4晶体中钒元素为+5价.同时测试了常温下SrxGd1-xVO4晶体的拉曼光谱,发现随着Sr2+离子浓度增加,在884cm-1处的VO4反对称伸缩振动逐渐增强,表明Sr2+离子的掺入影响了GdVO4晶体的拉曼性能.     

The Role of Impurity Precipitation on Ionic Conductivity of NaCl:Sr System

Ionic conductivity studies of NaCl crystals doped with 1 mole% of strontium both in as grown state and after quenching them from 550°C indicate that the conductivity depends on the impuritiy precipitates. It is found that all conductivity plots of pure NaCl, NaCl:Sr and NaCl:Sr crystals quenched from 550°C are straights lines, both in extensive and intrensic regions. The conductivity of NaCl: Sr system is always less than that of pure NaCl crystal. The results are explained on the basis of state of dispersion of impurities.     

Thermoluminescence and optical absorption studies of NaCl: Gd2+ crystals

Thermal annealing of X-irradiated point defects in gadolinium doped NaCl crystal is investigated by Thermoluminescence (TL) and optical absorption methods. The results of the influence of pre-heat treatment and optical bleaching on glow curves and the production of Z₁-centres are discussed.     

The effect of divalent impurity state on the microhardness of NaCl crystals

The microhardness and bulk density variations with annealing temperature have been measured in NaCl crystals doped with Ca²⁺, Cd²⁺, Ni²⁺, and Pb²⁺. Both characteristics are not affected by coherent metastable precipitation while incoherent precipitation produces either hardening or softening depending on the impurity phase type (stable or metastable). The results support the suggestion that aggregates and coherent precipitates are cut through by dislocations whereas incoherent precipitates are by-passed via the Orowan looping mechanism.     

Role of Z1 centres in radiation hardening of NaCl:Ba2+ crystals

Radiation hardening studies of undoped NaCl and NaCl crystals doped with barium have been carried out both in the as-grown state and after quenching them from 650°C. It is observed that the radiation hardening is more in doped crystals and the results are explained taking into consideration the role of Z₁-centres.     

Influence of preliminary thermomagnetic treatment on the yield point of NaCl: Ni Crystals

The influence of preliminary annealing (3 h, 1000 K), subsequent quenching in liquid nitrogen, and short magnetization in a constant magnetic field (0.5 h, 0.48 T) prior to deformation on the yield point of NaCl: Ni crystals is discovered. The effect depends on the time of sample storage between quenching and magnetization and is maximal 40 h after quenching.     

Influence of La3+ ions on growth and NLO properties of KDP single crystals

Single crystals of pure and Lanthanum added KDP crystals were grown from aqueous solution. The influence of La³⁺ ions in KDP crystals is studied. Isolated centers are formed by La³⁺ ions in KDP structure along (100) plane. La³⁺ ions incorporated into superficial crystal growth layer and slightly affect the growth process as they generate weak lattice stresses. The creation of these weak lattice stress is confirmed by Vickers's micro hardness test. The HRXRD analysis showed reduced structural defects in the La added KDP in the (100) plane than pure KDP. The incorporation of La in the crystal was confirmed by EDAX analysis. The Kurtz's powder SHG efficiency was found to be 1.5 times that of pure KDP. The UV‐Vis transmission spectra of La added KDP showed excellent transmittance from 1100 nm to 340 nm and did not show any change in lower cutoff wavelength with respect to pure KDP. Laser damage threshold value has been determined using Q‐switched Nd:YAG laser operating at 1064 nm and with 65 ns pulses in single shot mode. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of some Me2+ impurity ions on the lattice parameter of KCI crystals

The effect of concentration of substitutional Ca²⁺, Sr²⁺, Ba²⁺ and Pb²⁺ ions on the lattice parameter of KCI crystals is examined. The amount of lattice contraction induced by the alcaline earths ions qualitatively correlates with the pertinent ionic radii values (relative unit cell contraction induced by one impurity dipole amounts to −0.905, −0.110 and −0.020 for Ca²⁺, Sr²⁺ and Ba²⁺ ions, respectively). The initial drop of lattice parameter observed at low Me²⁺ concentration is tentatively ascribed to the drop of dislocation density. In Pb²⁺ doped crystals except for the above initial drop, at higher dopant concentration no effect upon the lattice parameter is found.     

Microstructural Effects of Mn2+ ions in ZnO Nanoparticles

Semiconducting ZnO nanoparticles with manganese content 0 at. %, 5 at. % and 10 at. % were prepared by co‐precipitation technique and XRD reveals that the average crystallite size D is 10.2 nm, 7.62 nm and 7.06 nm respectively. The individual contributions of the size and strain to the XRD peak broadening were investigated by Williamson‐Hall (W‐H) analysis. The strain, stress and energy density were calculated more precisely by uniform deformation model (UDM), uniform stress deformation model (USDM), uniform deformation energy density model (UDEDM) and size‐strain plot (SSP) method. The average particle size from HRTEM analysis is 13 ± 2 nm. The evaluated average crystallite size from the W‐H analysis and SSP method is commensurate with the particle size from HRTEM. Diamagnetic to ferromagnetic phase transition observed is interpreted interms of the anisotropic strain due to the dopant.     

Density,Colourability and Conductivity of Sr2+ Doped KCl Crystals

The measurements of colourability and density changes in KCl crystals with different Sr²⁺ contents point to the presence of two separate doping ranges in which different mechanisms of Sr²⁺ incorporation are active. Below 350 ppm Sr/KCl substitutional incorporation and above 350 ppm Sr/KCl precipitation of a second phase predominates. The latter process is accompanied by the formation of larger vacancy clusters. Ionic conductivity measurements imply that in the range between 80 and 350 ppm the aggregation of Sr²⁺ [+] dipols takes place.