Red-shift in the photostimulation of the X-ray storage phosphor RbBr:Ga+

Abstract

By means of magnetic circular dichroism of the optical absorption and photostimulated luminescence (PSL) the X-ray induced formation of F_A and F centres in RbBr:(Ga⁺, Li⁺) was investigated. It turnes out that RbBr:Ga⁺ co-doped with 1% Li⁺ in the melt reveals the largest red-shift of the PSL excitation bands to 790 nm, whereby the F_A to F ratio increases up to about 10% with decreasing X-ray dose. This is more than statistically expected (6%). High X-ray doses destroy F_A centres. However, up to 15% of the simultaneously generated F centres could be converted into the F_A species by appropriate bleaching with 633 nm light into the F centre absorption band.     

Thermoluminescence emission spectra and optical bleaching of oligoclase

Thermoluminescence (TL) spectra of oligoclase samples have been recorded in the temperature range from 300 to 700 K and the wavelength range from 300 to 850 nm. Like other feldspars, oligoclase produces blue (peaking at 460 nm) and red (peaking at 765 nm) emission bands. The maximum of the red emission occurs 20 K lower than that of the band. Optical bleaching was performed at wavelengths varying from 360 to 800 nm. Bleaching of artificially irradiated oligoclase causes a decrease of the TL signal. The bleaching efficiency increases with descreasing with wavelegth. Bleaching does not only influence the height of the glow curve but also the shape. An interesting observation is that ratio of the blue and red band intensities is not affected by a bleaching procedure. No evidence has been found that bleaching influences the shape of the emission spectra. The correlation between the blue and red bands is discussed.     

Blue emission in Ti-sapphire laser crystals

The time resolved emission spectrum of the blue band of Ti:sapphire laser crystal has been investigated as a function of temperature (range 10–290 K) and UV (266 nm) laser excitation intensity. Two blue emission bands, centred at 420 nm and 460 nm, have been detected. The 420 nm band is attributed to Ti⁴⁺ centres whereas the 460 nm one is proposed to be due to Ti³⁺ ions. The evolution of the emission spectrum vs the UV excitation intensity has shown that the concentration of Ti⁴⁺ centres is increased under UV irradiation at the cost of the centres responsible for the 460 nm band.     

Dose response of thermoluminescence emission spectra of LiF:Mg,Ti with different Mg, Ti impurity concentrations

The dose response of the TL emission spectra of an LiF:Mg,Ti (TLD-100) sample and three LiF:Mg,Ti samples with different impurity concentrations (0–6 ppm Ti and 80–100 ppm Mg) have been measured. At a dose less than 22 Gy the emission spectrum of the TLD-100 sample comprises one emission band at 420 nm. The sample without Ti shows also one emission band but now at 620 nm. The spectra of the other two samples comprises two emission bands at 420 nm and 620 nm of which the intensity of the 420 nm band increases with increasing Ti concentration. The dose response of the glow peaks is different for peaks at different temperatures and emission bands. From these observations it can be concluded than in LiF:Mg,Ti at least some of the traps and luminescent centers are coupled.     

Colour centres in microcrystalline powders of alkali halides

Abstract

Powders of twelve alkali halides have been coloured in an electrodeless discharge. Due to the simultaneous production and bleaching of F centres, F aggregate centres could be produced in an adequate concentration. From their study it has been concluded that powders behave as deformed single crystals. It could also be shown from this study that the interaction between colour centres and dislocations is lattice dependent and varies regularly as cation changes from Li⁺ to Rb⁺, and anion changes from F ^?to I^?.     

The effect of packing density on luminescence of amorphous SiO<Subscript>2</Subscript> nanoparticles

Photoluminescence of amorphous SiO₂ nanoparticles compressed in the form of tablets is studied under exposure to UV radiation. The observed luminescence spectrum is a broad band extending from the excitation wavelength to 700 nm and with a maximum at ~470 nm. The spectrum can be decomposed into two Gaussian components with maxima at ~460 and ~530 nm. As the pressure applied for sample preparation increases, the integrated intensities of these bands change in opposite directions—the intensity of the short-wavelength band increases, while that of the long-wavelength band decreases. It is concluded that these bands are due to different luminescence centers of silicon dioxide located on the surface and in the bulk of SiO₂ nanoparticles.     

The colouration of CaF 2 crystals by keV AND GeV ions

CaF 2 crystals have been implanted with a variety of ions of widely different energies and mass. Effects have been monitored using optical absorption in the range 120-750 v nm. This includes the vacuum UV region. For 100 v keV ions (Al, Mg, Kr) we observe extrinsic colloid bands in the case of implanted metal ions at high fluences (10 17 v ions v cm 2 ) but no colour centres (F, F 2 etc). For GeV ions (U, Ni) we observe prominent absorption bands in the visible region at fluences of 10 12 v ions v cm m 2 attributed to extrinsic calcium colloids. New optical features are discussed including an absorption band near 185 v nm in the VUV and bands at 604 v nm and 672 v nm in the visible region.     

BaClxBr2-x∶Eu2+材料光激励光谱及色心研究

采用高温固相法制备了BaClxBr2-x∶Eu2+光激励发光材料,利用XRD、激发、发射以及激励光谱研究了所制备材料的结构和光学性能。XRD图像表明所制备的材料为单一纯相,随X值增大,衍射角向大角度偏移。发射光谱中位于405nm的窄带谱峰,由Eu2+的4f65d→4f7能级跃迁所引起,监测405nm发射峰,所得激发光谱是位于250～380nm之间的宽带,谱峰位于303nm;光激励波段位于480～800nm,激励峰位于575nm。通过光谱曲线拟合,发现激励光谱由550,610和685nm左右的光谱叠加而成,分别对应F(Cl-),F(Cl-Br),F(Br-)色心,激励峰随Cl/Br比值增加而蓝移。     

Dy3+掺杂Sr1-xCaxMoO4的制备及发光性能研究

采用高温固栩法制备了Dy<'3+>掺杂的Sr1-xCaxMoO<,4>荧光粉.利用XRD、SEM、激发发射光谱以及色参数等研究了所制备荧光粉的结构和发光性能以及x值埘荧光粉性能的影响.XRD图像农明当x=1和x=0时样品为CaMoO<,4>和SrMoO<,4>单一相.SEM 图像表明在750℃下煅烧3 h制备的样品粒径为0.2～1.0μm,适合同态发光器件的要求.监测576 nm得到的样品的激发光谱由250～340 nm之间的一个宽带和340～460 nm之间的一系列尖峰组成.改变Sr/Ca的值,电荷迁移带激发峰位置发生变化,而窄带跃迁的激发峰强度发生变化.用350 nm波长激发样品得到的发射谱由峰值位于480和576 nm的两个窄带组成,它们是由和跃迁引起的.黄色发射峰和监色发射峰的强度比Y/B随着Sr/Ca比值的变化而变化.     

Ge：SiO2的光敏缺陷的研究

研究了Ｇｅ；ＳｉＯ２光敏缺陷的特性，分别在４８８ｎｍＡｒ离子激光与１９３ｎｍＡｒ准分子激光作用下，由紫外吸收带，激光荧光的测量实验及电子自旋共振实验，发现光纤中５．１ｅＶ锗缺陷吸收带实验上是由５．０６ｅＶ可光致漂白带与５．１７ｅＶ不可漂白带组成；２９５ｎｍ的激发荧光与５．０６ｅＶ的缺氧锗缺陷对应，随５．０６ｅＶ缺陷吸收带的漂白而衰减；     

The primary stages of the charge carrier photogeneration in C60 films studied by the 100-fs laser pulse pump-probe method

The primary stages of photoinduced processes are studied in thin C₆₀ films by the femtosecond laser pump-probe method. The films were excited by 100-fs laser pulses with photon energies above (wavelengths 345 and 367 nm) and below (645 nm) the mobility threshold, the fraction of excited molecules being no more than several percent. Upon probing in the spectral range from 400 to 1100 nm, several regions with substantially different decay kinetics were observed in the difference spectrum, which is caused by the simultaneous presence of several relaxing components. The appearance of the 465-and 500-nm bleaching bands in the difference spectrum upon excitation by photons with energies both above and below the mobility threshold, which are typical for electroabsorption spectra, suggests that charge carriers are produced in both these cases. The observed dependence of relaxation on the oxygen amount in the sample volume suggests that during excitation both charged (electrons and holes) and neutral (excited molecules) components are produced. The fraction of charged components is greater upon excitation into the fundamental band. The appearance of the 500-nm absorption band delayed by 10^?13–10^?14 s, the delay being increased in the presence of oxygen, was attributed to the formation of excited anions due to the capture of electrons by C₆₀ molecules. It is concluded that upon excitation of the films by photons with the energy below the mobility threshold, charge carriers are produced due to two-photon absorption rather than due to singlet-singlet annihilation. When the films are excited by photons above the mobility threshold, the primary charge carriers are produced by direct optical excitation.     

Radiation defects in Ce-activated fluorobromozirconate glass-ceramic X-ray storage phosphors

We report on a photostimulated luminescence (PSL) effect in Ce-doped fluorobromozirconate glasses. Small hexagonal or orthorhombic BaBr₂ crystallites are formed in the glass upon annealing. The PSL shows a (381,415) nm doublet which is due to the 5d–4f luminescence of Ce³⁺ in the orthorhombic BaBr₂ crystallites embedded in the glass matrix. The stimulation band of the PSL peaking at 580 nm is probably due to perturbed F centres in the crystallites. After X-irradiation the magnetic circular dichroism of the optical absorption showed a broad band in the spectral range between 440 and 800 nm, having a derivative-like line shape centred at about 600 nm. The spectrum consists of two overlapping bands: one, derivative-like, belongs probably to F-centres, whereas the second band, superimposed on the low-energy region of the F-centre band, is due to a hole centre.     

Optical absorption spectrum of the U centre in SrCl2

Studies of the correlation between i.r. and u.v. absorption spectra show that the u.v. absorption band of U centres is peaked at 212.3 nm. The weak peak observed at 233 nm is probably due to an impurity and some of the experimental results allow us to assume that it can be O^2-.The absorption band shape of U centres is very similar to that of F centres in SrCl₂. The second moment variations of these bands vs temperature can be interpreted in terms of an effective phonon frequency of 93 cm^-1.     

Photoionization processes in F aggregate centres of LiF crystal

Extensive studies have been carried out on the optical conversion of F and F-aggregate colour centres produced in lithium fluoride single crystal on gamma irradiation. Using 308 nm XeCl laser it has been shown that significantly large population build-up of F ₃ ⁺ centre and reduction in the population of undesirable F₂ centres can be achieved in gamma irradiated crystal at room temperature due to multistep photoionization processes. These and other investigations have provided a scheme for possible laser action based on F ₃ ⁺ colour centres in LiF crystal at room temperature.     

C_(60)在室温有机溶剂中荧光的研究

本文在室温下对C60分别在吡啶、甲苯和乙腈中的荧光了研究,实验表明:C60在吡啶中的荧光由以440nm、570nm和700nm为中心的三个荧光带组成;C60在甲苯中的荧光由以430nm和700nm为中心的两个荧光带组成;C60在乙腈中的荧光由以570nm和700nm为中心的两个荧光带组成。经比较分析发现C60-有机溶剂体系700nm区域的荧光带的发射与溶剂的种类无关,而440nm和570nm区域的荧光带及其精细结构可以反映C60与溶剂分子的特殊相互作用。进一步提出C60-吡啶体系以570nm为中心的荧光带是由吡啶分子通过含孤对电子的N与C60形成的电荷转移络合物发出的。     

UV–visible reflectance spectra of nanocrystalline silver compacted under different pressures

Nanocrystalline silver samples compacted under different pressures have been studied by X-ray diffraction and ultraviolet–visible reflectance spectroscopy. It is shown that the reflectance spectra exhibit an intense band at 315 nm, three weak bands at about 240, 380 and 490 nm, and a long tail at the long-wavelength side. Their origins are given. With increasing the compacting pressure, an opposite peak-shift effect of the surface plasmon resonance (SPR) was observed. It is concluded that the collaborating effects of particle aggregate and the unit-cell contraction both induced by the compacting pressure can explain these variations.     

Radiation damage and decay characteristics of zinc selenide emission bands and their equivalence to zinc sulphide emission bands

Irradiation of zinc selenide at ～ 20°K with electrons capable of displacing zinc atoms results in the production of cathodoluminescence emission bands at 610 and 630 nm. Enhancement of the 630 nm emission band by electron damage requires the presence of copper in the samples. These emissions have been shown to give a peak energy shift to lower energies after excitation, as is characteristic of donor-acceptor pair recombination. It is concluded that the 610 and 630 nm emission bands of zinc selenide are equivalent to the self-activated and copper green emission bands of zinc sulphide. The 530 nm emission band of zinc selenide is not sensitive to electron damage, shows no time shift and is thought to be equivalent to the copper blue emission of zinc sulphide.     

Absorption phenomena in multicomponent phosphate glasses with Mn

The absorption and ESR spectra of multicomponent alumino-phosphate glasses doped with manganese (0·2–20 mol %) has been measured and compared with the absorption spectra of manganous and manganic ions in model solutions. The unirradiated glasses show in ultraviolet region increasing absorption below 200 nm with the shoulder at 235 nm and the absorption bands due to manganous oxygen complexes in octahedral symmetry. They are similar to the absorption bands of Mn²⁺ in concentrated H₃PO₄ acid. In irradiated glasses the bands at 200, 235, 275 (only if Mn is present) and a broad band at 540 nm appear. After the annealing at 450 C all radiation-induced bands disappear and the bands at 235 nm is more pronounced. The Mn³⁺ in H₃PO₄ solution exhibit the absorption spectrum with a weak band at 530 nm and a very intense band at 270 nm. It is therefore proposed that both the 540 and 275 nm bands in irradiated glasses can be assigned to octahedral oxygen complexes of Mn³⁺, i.e. to hole centres. The band at 200 nm which is practically independent of the modifiers (Be, Mg, Ca, Sr and Ba) is, therefore, associated with electron centres (electrons trapped in non-bridging oxygen vacancies). It is suggested that the band at 235 nm in irradiated and annealed glasses is associated with irreversible structural changes.The authors wish to express their appreciation to H.Dvoáková for preparing the solutions and E.Linhartová for careful measurements.     

Emission spectra of KBr:Sn2+

Crystals of KBr:Sn²⁺ irradiated in the A₁, A₂, B or D absorption bands exhibit strong emission in the region of 500 nm. The dependence of this emission on excitation wavelength in the A absorption band shows the 500 nm emission band to be a doublet. This doublet structure is due to electrostatic perturbation from a nearby cation vacancy. It is not possible from emission spectra alone to decide on the actual symmetry of the A_T1 and A_T2 centres responsible for the emission doublet but the various possibilities are discussed. Quenching experiments show that a small emission band at 700 nm is due to Sn²⁺ dimer centres. A series of weak emission bands on the high-energy side of the A_T band are ascribed to emission from the relaxed excited B and D states.     

Fluorescent probe based on proton transfer in 4′-(diethylamino)-3-hydroxyflavone: Spectral and luminescent characteristics upon selective excitation

The spectral characteristics of acetonitrile solutions of 4′-(diethylamino)-3-hydroxyflavone dye with dual fluorescence are studied under selective excitation. This dye is a structural analog of 3-hydroxyflavone and exhibits excited-state proton transfer, which, in contrast to 3-hydroxyflavone, has a thermodynamic rather than a kinetic character. The fluorescence spectra at different excitation photon energies and the excitation spectra of different fluorescence bands are studied. It is found that the intensity ratio of the normal and tautomeric fluorescence bands lying near 507 and 570 nm, respectively, depends on the excitation wavelength, namely, this ratio is 1.45 and almost does not change in the region of the main absorption band (370–420 nm), while, in the region of the second singlet band (near 280 nm), it decreases to 1.15. This can be explained by an increase in the probability of proton transfer with formation of a tautomeric form in the case of excitation into the second band. Another interesting feature is the existence of a latent third emission band peaked at 535 nm, which was found and reliably recorded upon excitation at wavelengths of 470–500 nm. Addition of water quenches this emission, which indicates that it belongs to the anionic form of the dye.