Low-temperature electrolytic coloration and spectral property of ammonium alum crystals

Ammonium alum crystals are colored electrolytically using a pointed cathode and a flat anode at low temperatures and under various voltages. SO₃^?, SO₂^? and O₃^? hole-trapped centers are produced in colored ammonium alum crystals. Characteristic absorption bands of SO₃^?, SO₂^? and O₃^? hole-trapped centers are observed in absorption spectra of colored ammonium alum crystals. Production and conversion of hole-trapped centers are explained. Current–time curves for electrolytic coloration of ammonium alum crystal and their relationship with electrolytic coloration process are given.     

Electrolytic coloration and spectral properties of OH- and Cu-codoped NaCl crystals

OH⁻- and Cu⁺-codoped NaCl crystals are colored electrolytically by using a pointed anode and a flat cathode at various temperatures and under various voltages. Absorption and fluorescence spectral properties of colored crystals are investigated. Absorption, excitation and fluorescence spectra reveal existence of V₂, V₂^m, V₃, OH⁻, U, U_A, O²⁻–V_a⁺, O₂⁺, Cu⁺, Cu⁰, Cu⁻ and OH⁻-perturbed Cu⁺ color centers in colored crystals. Formations of color centers are explained.     

Electrolytic coloration and spectral properties of hydroxyl-doped potassium chloride single crystals

Hydroxyl-doped potassium chloride single crystals are colored electrolytically at various temperatures and voltages using a pointed cathode and a flat anode. Characteristic OH⁻ spectral band is observed in the absorption spectrum of uncolored single crystal. Characteristic O⁻, OH⁻, U, V₂, V₃, O²⁻-V_a⁺, F, R₂ and M spectral bands are observed simultaneously in absorption spectra of colored single crystals. Current-time curve for electrolytic coloration of hydroxyl-doped potassium chloride single crystal and its relationship with electrolytic coloration process are given. Production and conversion of color centers are explained.     

Electrolytic coloration of air-grown sodium fluoride crystals

Air-grown sodium fluoride crystals were colored electrolytically by using a pointed cathode at various temperatures and electric field strengths, which should mainly benefit appropriate coloration temperatures and electric field strengths. , F, M, N₁, N₂ color centers and O²⁻-F⁺ complexes were produced in the colored crystals. Current-time curves for the electrolytic colorations were given, and activation energy for the V color center migration was determined. The formation of the color centers was explained.     

Electrolytic coloration of O2-doped NaCl crystals

O₂²⁻-doped NaCl crystals are colored electrolytically by using a pointed cathode and a flat anode at various temperatures and voltages, which mainly benefit from appropriate coloration temperatures and voltages as well as anode structure of used electrolysis apparatus. Characteristic OH⁻, U, V₂^m, U_A, V₂, V₃, O²⁻-V_a⁺ complex, F, R₁, R₂ and M absorption bands are observed in absorption spectra of the colored crystals. Production and conversion of color centers in electrolytic coloration is explained. Current-time curves for electrolytic colorations and their relationships with electrolytic colorations were given.     

Formation of H<Subscript><Emphasis Type="Italic">a</Emphasis></Subscript><Superscript>-</Superscript> hydrogen centers upon additive coloration of alkaline-earth fluoride crystals

The mechanism of coloration of alkaline-earth fluoride crystals CaF₂, SrF₂, and BaF₂ in calcium vapors in an autoclave with a cold zone is studied. It was found that the pressure in the autoclave upon constant evacuation by a vacuum pump within the temperature range of 500–800°C increases due to evaporation of metal calcium. In addition to the optical-absorption bands of color centers in the additively colored undoped crystals or to the bands of divalent ions in the crystals doped with rare-earth Sm, Yb, and Tm elements, there appear intense bands in the vacuum ultraviolet region at 7.7, 7.0, and 6.025 eV in CaF₂, SrF₂, and BaF₂, respectively. These bands belong to the H_a ^- hydrogen centers. The formation of hydrogen centers is also confirmed by the appearance of the EPR signal of interstitial hydrogen atoms after X-ray irradiation of the additively colored crystals. Grinding of the outer edges of the colored crystals leads to a decrease in the hydrogen absorption-band intensity with depth to complete disappearance. The rate of hydrogen penetration inside the crystal is lower than the corresponding rate of color centers (anion vacancies) by a factor of tens. The visible color density of the outer regions of the hydrogen-containing crystals is several times lower than that of the inner region due to the competition between the color centers and hydrogen centers.     

Zur Bildungskinetik der F-Folgezentren in KCl

Following the same procedure as in part I the formation of Z₁-centers under Flight irradiation was investigated in additively colored KCl crystals doped with Ca⁺⁺ and Sr⁺⁺ ions. The measurements show that again F′-centers and empty anion vacancies are the first reaction product and determine the rate of Z₁-center formation. The temperature dependence and rate of the Z₁-center formation is in agreement with the corresponding results on F _A -center formation, demonstrating that Z₁-centers are formed as the consequence of an ionic process and not a mere electronic transfer. It is concluded that again empty anion vacancies or F′ centers diffuse randomly in the lattice (activation energy 0.6 eV) until they are captured at an impurity site. Arguments are presented that these impurities are divalent cation/vacancy complexes, so that the model of the Z₁-center should be a combination of the F-center with this complex. The independence of the Z₁-band of the nature of the divalent cation indicates the assoziation of the F-center to the vacancy-side of the complex. A characteristic delay period in the Z₁-center formation can be accounted for by a non-statistical distribution of F-centers and divalent cations to each other. This is a necessary consequence of the high temperature dynamical equilibrium between these imperfections which is frozen in by the quenching of additively colored crystals. A direct proof for this interpretation is the absence of the delay period in crystals where the F-centers are formed by x-irradiation at room temperature.     

Passive Q-switches for Nd:hosted Solid State Lasers

The currently available Nd:hosted lasers utilizing passive Q-switches: a plastic dye sheet, a LiF:F₂- color center crystal, a Cr⁴⁺:YAG crystal or a RG1000 colored glass filter have been investigated in detail and the results summarized for comparison purposes for the first time. We first briefly summarize our own and others’ past studies, and report on recent new results concerning the use of Cr⁴⁺:YAG crystals and RG1000 colored glass filters as Nd:hosted laser passive Q-switchings. We then investigate in detail solid state laser system design using the above four passive modulators. Typical interpretations are given based on characteristic features of the materials, such as their saturation intensity and relaxation times. The results are then explained via adequate equations derived with respect to the relevant physical parameters of the materials. The optical dersity selection of plastic dye sheet passive Q-switching for the Nd:YAG laser system design is verified quantitatively, and the slope efficiencies from plastic dye sheet passive Q-switched operation by single pulse and multiple pulse bursts are investigated. The multi-peak Q-switched pulse timing phenomena are presented as well. The outstanding annealability, long lifetime, inexpensiveness and high repetition rate operation of LiF:F₂- crystals are highly recommended.     

Elastic strain and coloration pattern in natural quartz crystals

Very small elastic strains (tilts of the order of 0.25 sec of arc and dilationsΔd/d?10^?6, whered is the spacing of net planes) have been observed in natural quartz crystals. According to their rocking curves which are of almost theoretical width, these crystals were commonly expected to be practically perfect crystals. On double crystal X-ray topographs a pattern was revealed of uniformly strained layers parallel to the rhombohedron faces (10¯11) and with thickness ranging between 20 and 200 microns. This fine structure strain pattern was correlated to the pattern of the optical coloration which could be produced by irradiating the originally transparent crystals with X-rays. A localincrease of coloration matched with a localcontraction of the lattice. Tilts occurred in transition zones between adjacent layers with slightly different lattice spacings. Strain and coloration patterns probably have as a common cause the deposition of layers with different impurity concentrations during the growth process of the crystals. Although no change of the strain as a result of the X irradiation could be detected in the colored layers in particular, experimental evidence has been found for anoverall expansion of the lattice of the order ofΔd/d?5×10^?7 due to X irradiation. This expansion seems to saturate at this low value and is probably caused by electronic processes connected with the coloration. Some aspects concerning the nature of the color centers have been discussed. It seems likely from the results of the strain measurements that both sets of layers, colored and transparent ones, play a combined role in coloration.     

Time-resolved spectroscopy of natural and synthetic BeO crystals

The results of comparative luminescence investigation of natural and synthetic BeO crystals are presented. Time-resolved luminescence (2.5–8 eV) and luminescence excitation spectra, and the kinetics of glow decay were measured using ultraviolet-vacuum-ultraviolet (VUV) synchrotron radiation (5–22 eV) or x-radiation (50–620 eV or 3–62 keV) ranges. X-ray and thermostimulated luminescence of natural BeO crystals were compared to the glow of additively colored synthetic crystals. The characteristic luminescence of F and F ⁺ centers was found in natural crystals. In synthetic crystals similar luminescence is observed only after additive or radiation coloration by virtue of the creation of F ⁻ and F ⁺ centers on anion vacancies. The defects found in the crystal lattice of a natural BeO crystal testify to the degree of mineral metamictization of the given deposit.     

F<Stack> <Subscript>3</Subscript> <Superscript>−</Superscript> </Stack> molecular ions in fluoride crystals

The UV absorption spectra of F₃^? molecular ions in LaF₃, SrF₂, CaF₂, and BaF₂ crystals doped with rare-earth elements are studied. Comparison of radiation-colored and additively colored crystals reveals the absorption bands of F₃^? hole centers in the region near 6 eV. Nonempirical calculations of optical transitions agree well with experimental results.     

Luminescence and ESR detected hydrogen related electron traps in yellow-colored CaO crystals

Abstract

Electron spin resonance of the off-center H^2- ions replacing oxygen in additively colored CaO crystals has been investigated. Electron tunneling in F… H^? pairs is essential in photoconversion and thermoluminescence of CaO at low temperatures.     

溴化钾晶体电注入着色和光谱特性

用自行研制的电注入装置,在693 K温度下施加DC 1 200 V电压、对溴化钾晶体进行电注入并使之有效着色。在着色溴化钾晶体中产生大量F,R,M,N类和一些新的未知色心,并给出色心形成和转化机理。对着色晶体进行系统光谱测量和分析,用解谱法将相应色心光谱带从测得光谱中合理地分解出来,并精确确定其光谱参数。     

Fast nonlinear optical mechanism of photoconversion in systems of lyotropic ionic liquid crystals–viologen impurities

We study a new nonlinear optical mechanism of reversible photoconversion between excited dimers and cation radicals, the reduction products of electrochromic molecules (viologens), in lyotropic ionic liquid crystals of metal alkanoates. The results of the theoretical study are compared with experimental data obtained from dynamic holographic recordings as well as nonlinear absorption measurements. The estimated value of the photoconversion probability is higher than the probability of non-radiative relaxation of excited molecules. The value of the cubic nonlinearity is χ ^(3)?～?4?·?10^?7?esu for colored cells of these materials.     

Two types of additional absorption spectra in CaF2 crystals

A study of two types of additional absorption spectra observed in colored CaF₂ crystals is reported. The spectral shape for the additively colored crystal is governed by the experimental conditions; during photochemical coloring, it depends on the thermal prehistory of the sample. In all cases, a spectrum consisting of bands at 370 and 560 nm appears in crystals having a band near 200 nm. An additional band appears at 560 nm in the Smakula spectrum at high-irradiation doses; there are three stages in the increase of this band with increasing dose. A similar dependence on the radiation dose is observed for the 560-nm band in synthesized CaF₂ crystals. It is suggested that this band is due to defects produced in the lattice during the irradiation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 4, pp. 56–64, April, 1969.     

V color centers in electrolytically colored hydroxyl-doped sodium chloride crystals

Hydroxyl-doped sodium chloride crystals were successfully colored electrolytically by using pointed anode and flat cathode at various temperatures and under various electric field strengths. V₂ and V₃ color centers were produced in the colored crystals. Current-time curves for the electrolytic colorations were given, and activation energy for the V₂ and V₃ color center migration was determined. Production of the V₂ and V₃ color centers and formation of current zones for the electrolytic colorations of the hydroxyl-doped sodium chloride crystals are explained.     

Energy transfer among color centers in LiF crystals

In colored LiF crystals there are many absorption and emission bands which cover a wide region of the spectrum from 200 up to 1 300 nm without breaking the continuity. In the frame of these favourable conditions we have performed some experiments of energy transfer among various color centers. The results indicate the existence of efficient exchanges of radiative energy among several bands by using only one exciting wavelength. In particular, the emissions of the F₃ ^- and F₂ ^- color centers centered at 900 and 1 100 nm, respectively, have been observed by pumping at 672 nm completely outside their absorption bands. Received 25 June 2001 and Received in final form 16 July 2001     

Color centers in heavily irradiated CsI(Tl) crystals

The absorption and luminescence properties of CsI(Tl) crystals colored by irradiation are studied by the method of the time-resolved spectroscopy. The scheme of the electron transitions in CsI(Tl) crystal is suggested to explain the appearance of the color centers under exposure to the near-UV light. It is established that either of the two types activator color centers holds the charge carrier with opposite sign. The model of the hole Tl²⁺v_c⁻ activator color center is suggested. According to the model the positive charge of Tl²⁺ ion is compensated by the negative charge of a close cation vacancy v_c⁻. The color center emission reveals in the cathode-luminescence spectrum of the colored CsI(Tl) crystal. The high-dose irradiation of CsI(Tl) crystal results in the reduction of the decay time of the near-thallium self-trapped excitons (STE) emission. The decay kinetics of Tl²⁺v_c⁻ emission contains the time components typical for the decay kinetics of near-thallium STE emission. The reason of the observed effects is the energy transfer from the near-thallium STE excitons to the color centers via the inductive-resonant mechanism.     

Radio and thermoluminescence studies in CsI doped with F centers

Radioluminescence, thermoluminescence and u.v. excitation measurements in CsI additively colored crystals show a new luminescent component located at 2.5 eV. This is attributed to the radiative recombination of V_k centers with F centers. Another new component at 2.72 eV is observed only under u.v. excitation of 5.14 eV. This is related to the radiative recombination of localised excitons at F⁺ center sites (α band).     

着色KCl和KBr晶体色心的光谱特性及其零声子跃迁

详细研究了不同温度下着色ＫＣｌ晶体Ｒ２心和７５６．６ｎｍ零声子线以及着色ＫＢｒ晶体Ｒ２心零声子线的产生．利用恰当的热处理，可产生和增强零声子线，并给出了相应的物理解释．