Origin of the 420 nm Absorption Band and Effect of Doping Fluorine in PbWO4 Crystals

The electronic structures for three types of PbW04 (PWO) crystals, the perfect PWO, the PWO containing lead vacancy (PWO-Vpb) and fluorine doped PWO crystal (F^-：PWO), are systematically studied within the framework of density functional theory. The computational results show that the Pb 6s state situates below the valence band so that Pb^2 ions are unable to trap holes forming Pb^3 or Pb^4 to compensate for VPb^2-. The hole-trappers in PWO-Vpb are O^2- ions. Two of the longer-bond O^2- ions share a hole forming O2^3-, and four of the longer-bond oxygen ions trap two holes forming an associated color centre [O2^3--Vpb-O2^3-], which may be the origin of the 42Onto absorption band. It is also concluded that the doping of F^- would reduce the band gap and F^- ions substituting for O^2- can effectively restrict the formation of [O2^3--Vpb-O2^3-] and weaken the 42Onm absorption band and hence enhance the scintillation property of PWO.     

Comparative Studies of Rare-Earth Element Y-Doped In2O3 by First-Principles Calculations

In2O3 doped with rare-earth element yttrium shows improved optoelectronic efficiency. Here the structural properties and electronic structures of Y-doped In2O3 are investigated by using a first-principles approximation. For In1.9375 Y0.062503, the d site is the more stable site. The Y^3＋ interstitial has a low formation energy and is a possible interstitial defect, which would lead to shallow and abundant donors without sacrificing optical transparency. Since defects are universally distributed in In2O3 or doped In2O3, complex defect configurations are also calculated.     

Effect of Mg and Fe Doping on Optical Absorption of LiNbO3 Crystal through First Principles Calculations

Using first principles calculations, we investigate the structural, optical, and electronic properties of LiNbO3 （LN） and M doped LN （M=Mg, Fe）. The density of states are calculated to analyze the effect of doping Mg and Fe ions on the absorption spectra and electronic properties of LN. The results show an ultraviolet shift in the optical absorption edge of Mg-doped LN compared with that of intrinsic LN. On the contrary, the absorption edge of Fe-doped LN crystal reveals a red shift. The optical absorption spectra show an improved optical response in the visible range for Mg-doped LN, which significantly differs from that obtained for Fe-doped LN. The electronic excitations from the valence band to the conduction band of LN leads to an improved optical absorption response in the visible region as observed experimentally. The obvious changes of the doped LN crystal are found in some cases, which provide a helpful guide for preparing doped LN crystal.     

First-Principles Studies on Electronic Structures and Absorption Spectra of PbWO4 Crystals with Defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-c

Electronic structures and absorption spectra for perfect PbW04 （PWO） crystals and the crystal containing aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-have been calculated using density functional theory code CASTEP with the lattice structure optimized. The calculated absorption spectra of the PWO crystal containing the aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-exhibit two absorption bands peaking at 1.90eV （65Onto） and 3.02eV （41Onto）. It is predicted that the 420 and fiSOnm absorption bands are related to the existence of the aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-in the PWO crystal.     

Experimental and computational study of visible light-induced photocatalytic ability of nitrogen ions-implanted TiO2 nanotubes

Nitrogen-doped TiO2 nanotubes(TNTs)were prepared by ion implantation and anodic oxidation.The prepared samples were applied in photocatalytic(PC)oxidation of methyl blue,rhodamine B,and bisphenol A under light irradiation.To explore the influence of doped ions on the band and electronic structure of TiO2,computer simulations were performed using the VASP code implementing spin-polarized density functional theory(DFT).Both substitutional and interstitial nitrogen atoms were considered.The experimental and computational results propose that the electronic structure of TiO2 was modified because of the emergence of impurity states in the band gap by introducing nitrogen into the lattice,leading to the absorption of visible light.The synergy effects of tubular structures and doped nitrogen ions were responsible for highly efficient and stable PC activities induced by visible and ultraviolet(UV)light.     

VUV/UV/X-Ray Excited Luminescent Properties of Eu^3＋ and Pr^3＋ Doped BiSbO4

Absorption spectra of BiSbO4 are studied. The electronic structure calculated by the DFT shows that BiSbO4 is a semiconductor, with direct band gap 2.96 eV, which is consistent with UV-visible diffuse reflectance experiment. The host lattice emission band is located at 440 nm under VUV excitation. Eu^3＋ and Pr^3＋ doped samples have high luminescence efficiency in emitting red and green light, respectively. From the partial density of states, Eu^3＋ doped emitting spectrum, and the host crystal structure parameters, the relationship between structure and optical properties is discussed. It is found that the Eu^3＋ ions occupied Bi^3＋ sites, and there could be an energy transfer from Bi^3＋ ions to RE^3＋ ions.     

Active Loss of Light Yield of PbWO4：Y Scintillation Crystals After Irradiation

PWO crystals doped with yttrium were grown with the Bridgman method in platinum crucible and by using an indigenously developed resistive heating furnace. After an exposure of γ-ray from a ^60Co source, with the dose rate of lS rad/h for 20h, the light output increases for about 15%, accompanied with vanishing of an optical absorption band at 420 nm. The excitation and emission spectra of PWO crystals were measured before and after irradiation with different dose rates. The optical absorption band at 420nm was also found in the PWO sample annealed in oxygen-rlch atmosphere. It is suggested that the absorption band at 42Onm is related to Pb^3 point defects existing in the PWO crystal. The unusual change of light output after irradiation probably results from the transformation of lead ions from Pb^3 to Pb^2 .     

First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2

The electronic structures of Ag-doped rutile and anatase Ti02 are studied by first-principles band calculations based on density functional theory with the full-potential linearized-augmented-plane-wave method. New occupied bands are found between the band gaps of both Ag-doped rutile and anatase TiO2. The formation of these new bands can be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption.     

First-principles study on with nitrogen and anatase TiO2 codoped praseodymium

<正>The crystal structures,electronic structures and optical properties of nitrogen or/and praseodymium doped anatase TiO₂ were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on density functional theory.Highly efficient visible-light-induced nitrogen or/and praseodymium doped anatase TiO₂ nanocrystal photocatalyst were synthesized by a microwave chemical method.The calculated results show that the photocatalytic activity of TiO₂ can be enhanced by N doping or Pr doping,and can be further enhanced by N+Pr codoping.The band gap change of the codoping TiO₂ is more obvious than that of the single ion doping,which results in the red shift of the optical absorption edges.The results are of great significance for the understanding and further development of visible-light response high activity modified TiO₂ photocatalyst.The photocatalytic activity of the samples for methyl blue degradation was investigated under the irradiation of fluorescent light.The experimental results show that the codoping TiO₂ photocatalytic activity is obviously higher than that of the single ion doping.The experimental results accord with the calculated results.     

First-Principles Studies on the Electronic Structures and Optical Properties for the PbWO4 Crystal Containing V^2-pb

The electronic structures, dielectric functions, complex refractive indices and absorption spectra for a perfect PbW04 (PWO) crystal and the PWO crystals containing lead vacancy V^2-pb have been calculated using a full-potential (linearized) augmented plane-wave (LAPW) local orbitals (LO) method with the lattice structureoptimized. The peaks of the absorption spectra corresponding to the electronic transitions have been studied.     

+3价离子掺杂钨酸铅晶体发光性能和微观缺陷的研究

通过透射光谱、x射线激发发射光谱（XSL）的测试，研究了Bridgman法生长的几种不同+3价离子掺杂钨酸铅晶体的发光性能，并利用正电子湮没寿命谱（PAT）和x光电子能谱（XPS）的实验手段，对不同钨酸铅晶体的微观缺陷进行研究.实验表明，不同的+3价离子掺杂，对钨酸铅晶体发光性能的改善不同，并使得晶体中正电子俘获中心和低价氧的浓度发生不同变化.其中掺镧晶体的正电子俘获中心和低价氧浓度均上升，而掺钇和掺铋晶体的正电子俘获中心和低价氧浓度均下降，掺锑晶体则出现了正电子俘获中心浓度上升、低价氧浓度下降的情况.提 关键词： 钨酸铅晶体 +3价离子掺杂 正电子湮没寿命谱 x光电子能谱     

含铅空位的PbWO4晶体光学性质及其偏振特性的研究

利用完全势缀加平面波局域密度泛函近似，计算了含铅空位的PbWO₄（PWO）晶 体的电 子结构，模拟计算了复数折射率、介电函数及吸收光谱的偏振特性. 比较含铅空位的PWO晶 体与完整的PWO晶体的吸收光谱及其偏振特性，得到与铅空位相关的吸收光谱及其偏振特性 ，计算结果与实验结果基本相符. 计算得到的含铅空位的PWO晶体的光学偏振特性反映了PWO 晶体的结构对称性. 计算结果表明PWO晶体中350，420，550和680 nm的吸收带的出现与PWO 晶体中铅空位的存在直接相关. 关键词： 4晶体')" href="#">PbWO₄晶体 电子结构 光学性质 铅空位     

掺Gd3+,Y3+对PbWO_4低温热释光的影响

通过热释光方法研究了PbWO₄(PWO),PWO:Y³⁺,PWO:Gd³⁺多晶粉末及PWO,PWO:Y单晶的低温(<300K)热释光现象.多晶粉末中,掺杂Y³⁺或Gd³⁺都会大大降低甚至消除200K附近的热释光峰,同时产生新的热释光峰,分别位于125和150K(掺Y掺Gd).这表明掺三价离子除了起到电荷补偿作用以减少Pb³⁺,O^-浓度外,还可以产生新的陷阱能级.对于PWO:Y单晶,掺杂Y³⁺可以消除253K的热释光峰,即消除较深(～0.89eV)的陷阱,但PWO单晶中较浅的陷阱(～0.42eV)对应130K热释光峰仍然存在,对此进行讨论,它最可能源于氧空位缺陷.根据Pb³⁺,Gd³⁺,Y³⁺的电子库仑势不同,在PWO晶体中替代Pb²⁺后形成的电子陷阱深度有别(E_Pb>E_Gd>E_Y),从而解释了相应的热释光峰值温度的不同 关键词： 4')" href="#">PbWO₄ Y和Gd掺杂 热释光 陷阱     

First-principles study of color centers in PbMoO4 crystals

Electronic structures of PbMoO₄ crystals containing Mn ion impurities located at Pb²⁺ sites are studied within the framework of the fully relativistic self-consistent Direc-Slater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that Mn²⁺ ions have donor energy levers in the forbidden band, which may correspond to the yellowish color absorption band of PbMoO₄ as-grown in air. The new-formed Mn³⁺ ions have acceptor energy levers in the forbidden band, which may relate to the photochromic effect in PbMoO₄ crystal.     

Electrical conductivity and colour centres in Tl-doped KCl crystal

The electrical conductivity and optical absorption of potassium chloride crystals doped with different concentrations of thallium have been measured before and after X-irradiation. The optical absorption spectrum exhibits the characteristic Tl⁺ ion band at 247 nm. The extrinsic conductivity and the absorption coefficient at 247 nm increase with impurity addition upto a certain concentration. Further increase in impurities decreases them. Room temperature X-irradiation decreases the Tl⁺ ion band and produces the F band. F centre concentration is higher in lightly doped crystal compared to pure or heavily doped KCl. These results have been interpreted in terms of formation of interstitial potassium ions and positive ion vacancies in the Tl-doped KCl lattice due to large ionic radius of Tl⁺ ions. The impurity ions precipitate into TlCl phase when the doping is heavy.     

PbWO4晶体中的填隙氧及其对晶体光学性质的影响

运用GULP计算软件模拟计算了PbWO₄(PWO)晶体中不同位置的填隙氧原子点缺陷的生成能，计算结果表明：当填隙氧原子存在于(WO₄)^2-的周围时，填隙氧原子点缺陷的生成能最低；进一步运用基于密度泛函理论的全数值自洽DV-Xα方法计算了包含填隙氧原子的PWO晶体的态密度，计算结果表明：当填隙氧处在(WO₄)^2-的周围时，容易与(WO₄)^2-上的一个或两个氧离子相互作用形成分子离子O₂^2-或O₃^4-，通过分析这些计算结果，认为PWO晶体中350 nm吸收带的出现很可能与晶体中的氧分子离子有关.     

Studies on the origins of the absorption spectra in PbWO4 crystal

The electronic structures and absorption spectra for both the perfect PbWO₄ (PWO) crystal and the three types of PWO crystals, containing V_Pb²⁻, V_O²⁺ and a pair of V_Pb²⁻-V_O²⁺, respectively, have been calculated using CASTEP codes with the lattice structure optimized. The calculated absorption spectra indicate that the perfect PWO crystal does not occur absorption band in the visible and near-ultraviolet region. The absorption spectra of the PWO crystal containing V_Pb²⁻ exhibit seven peaks located at 1.72 eV (720 nm), 2.16 eV (570 nm), 2.81 eV (440 nm), 3.01 eV (410 nm), 3.36 eV (365 nm), 3.70 eV (335 nm) and 4.0 eV (310 nm), respectively. The absorption spectra of the PWO crystal containing V_O²⁺ occur two peaks located at 370 nm and 420 nm. The PWO crystal containing a pair of V_Pb²⁻-V_O²⁺ does not occur absorption band in the visible and near-ultraviolet region. This leads to the conclusions that the 370 and 420 nm absorption bands are related to the existence of both V_Pb²⁻ and V_O²⁺ in the PWO crystal and the other absorption bands are related to the existence of the V_Pb²⁻ in the PWO crystal. The existence of the pair of V_Pb²⁻-V_O²⁺ has no visible effects on the optical properties. The calculated polarized optical properties are well consistent with the experimental results.     

Mechanism of Th, Zr doping in PbWO4 crystals

To check the doping mechanism of trivalent ion doping in PbWO₄ (PWO) and verify the formation of dipoles [2M_Pb³⁺-V_Pb], the researches on an investigation of tetravalent ion (Th⁴⁺, Zr⁴⁺) doped PWO was conducted by dielectric loss spectroscopy, thermoluminescence and optical absorption spectroscopy. The doping mechanism of tetravalent ion doping is similar to that of trivalent ion doping, while the dipole defects should be formed more easily due to the convenience for the two defects V_Pb and M_Pb⁴⁺ to get close to each other. However, in the case of Zr⁴⁺ doping, Zr was found to enter interstitial sites because of its small ionic radius, with the introduced charges compensated by V_Pb far away and hence does not exert an obvious influence on the performance of this material. Thus, no dielectric relaxation was found in the DS (dielectric spectra) experiment.     

RAMAN STUDY ON (Pb) CENTERS IN SINGLE CRYSTALS OF ALKALI HALIDES DOPED WITH LEAD

Low frequency modes were observed in a series of alkali halides doped with lead after X-irradiation at 77K. The peak positions of the Raman signals are at 34cm^-1 for NaCl:Pb²⁺, 30cm^-1 for KCl:Pb²⁺,28cm^-1 for RbCl:Pb²⁺ and 22cm^-1 for KBr:Pb²⁺. They are assigned to the inelastic light scattering caused by the local vibration of X^-_i (Pb⁺) center, which consists of an interstitial halogen ion stabilized by a substitutional ion Pb⁺ . Polarized Raman measurements and Behavior Typer(BT) analysis show that the symmetry of the X^-_i (Pb⁺) center belongs to the point group C_3v A structure model of the X^-_i (Pb⁺) center is proposed based on the Raman data and the result of BT analysis.     

钨酸铅晶体中的偶极缺陷

在用阻抗谱研究PbWO₄（PWO）晶体的介电特性时发现，掺La³⁺的PW O晶体中存在典型的介电弛豫现象，它被归因于La³⁺进入Pb位并与铅空位V_Pb缔合 成偶极缺陷.这一结果不仅清楚地证明了PWO晶体中铅空位的存在，而且表明阻抗谱测试可以成为PWO晶体微结构研究的有力工具.以阻抗谱测试为主要工具，结合光吸收谱（包括红外谱）和x射线光电子能谱，阐明了在异价掺杂离子（3+，4+，5+以及3+和5+双掺）掺杂的PWO晶体中 关键词： 钨酸铅 偶极缺陷 异价掺杂 退火效应