Hole traps and thermoluminescence in Li2B4O7:Be

A trapped-hole centre with a high thermal stability is studied in Li₂B₄O₇:Be. EPR spectrum demonstrates a hyperfine splitting due to interaction of the trapped hole with a ⁹Be nucleus. The hole is trapped at the common vertex (bridging oxygen) of two adjacent BO₄ tetrahedra when Be²⁺ substitutes for B³⁺ in one of them. The centre is stable up to ≈500 K. The high-temperature thermoluminescence peak at 510–575 K occurs when the released holes recombine with trapped electrons. This peak shows an ultraviolet exciton-like luminescence band and also luminescence bands of casual impurities.     

Creation of electronic excitations and defects by vuv radiation (6-40 eV) in wide-gap solids

The processes of multiplication of electronic excitations (MEE), connected with the creation of secondary excitons or electron-hole (e-h) pairs by hot conduction electrons, are realized in wide-gap metal halides and oxides. In oxides, secondary e-h pairs can be also formed by 27-40 v eV photons due to L 1 VV Auger transitions (with the participation of 2s oxygen holes). The excitation spectra of luminescence and the creation spectra of electron F centres or hole V centres have been measured for Na 6 Al 6 Si 6 O 24 (NaI) 2x sodalites and MgO:Be, respectively, at 8-80 v K. A high local density of excitations has been revealed under MEE conditions in KBr and Br sodalites with self-trapping excitons and holes.     

稀土掺杂碱土金属硫化物晶体中的载流子俘获中心

研究了典型红外激励发光材料XS:Ra,Sm(X=Sr,Ca;Ra=Ce,Eu)的激励发光过程中电子与空穴的俘获中心及其转移过程,通过激发前后的红外吸收光谱的差异及吸收差与光激励谱的细微结构说明,电子俘获中心并不是Sm³⁺离子,但与Sm³⁺离子处于相邻的空间位置关系,Sm³⁺离子在载流子俘获与复合的过程中也没有发生价态或数量的变化,进一步的EPR谱研究表明Eu²⁺离子的价态在激发前后也没有发生变化。与共价性强的Ⅲ-Ⅴ族半导体晶体不同的是,在这类离子性较强的晶体中,载流子被杂质所引起的晶格缺陷而非杂质本身俘获。在多种发光中心的情况下,不同的激发波长可以使空穴束缚在不同的发光中心附近,随后产生不同的光激励发光。     

Exciton mechanism of energy transfer to F-centers in dosimetric corundum crystals

The optical absorption (OA) and thermoluminescence of oriented -Al₂O₃ crystals colored in aluminum vapor have been studied. Optical absorption measurements of an X-irradiated sample at the orientation EC₃ during isochronal annealing revealed mutual transformations of F- and F⁺-centers within the dosimetric peak from 380 to 500 K. The transformations occurred simultaneously with emptying of the electron trap whose OA is at 2.8 eV. The predominant F→F⁺ conversion, which could be explained by delocalization of holes, was observed in the low-temperature part of the peak near 380–440 K. From the available experimental data it was inferred that the simultaneous release of electrons and holes in the low-temperature part of the peak facilitated formation of excitons bound on F-type centers. The excitons transferred part of the energy stored in the irradiated crystal to F⁺- and F⁻-centers during thermal stimulation, leading to luminescence of these centers.     

Photoluminescence and photostimulated luminescence in the X-ray storage phosphor BaBr2 doped with cerium

In orthorhombic BaBr₂ : Ce³⁺ two kinds of luminescence bands at room temperature have been attributed to charge-compensated Ce³⁺ centres. One type was associated with potassium (or some other monovalent cation) on a neighbouring Ba site and another one associated with an unidentified defect. A third kind of emission, observed only as low temperature photoluminescence (PL), is ascribed to isolated Ce³⁺ ions. The charge-compensated Ce³⁺ complexes are active both in PL and photostimulated luminescence (PSL) following X-ray irradiation. The PSL is nearly as efficient as in the case of the commercially used X-ray storage phosphor BaFBr:Eu²⁺. The X-ray induced electrons are trapped in F-type centres whose band position is characteristic for the nearby Ce complex. As shown by the fingerprint character of the PSL itself, the hole partner in the recombination is also associated or identical with the same Ce complex.     

GaN深中心Zn的低温瞬态研究

本文研究了GaN:Zn的低温瞬态过程,同时测量了衰减中的时间分辨光谱,从两者测量的结果得出:2.89eV的光致发光寿命为300ns(2K).实验证实,Zn作为发光中心的同时也引起一些非辐射陷阱.2.89eV的瞬态曲线可分为两部分,在短时范围(1μs)内基本上是指数形式,可归结为导带中光激发的电子和束缚在ZnGa受主上空穴的复合.在长时范围(t>>1μs)内瞬态曲线则偏离了指数规律,相当好地符合Becqureal经验公式.     

Anharmonic V–V pumping and asymmetric electron-elementary excitation interaction in emission and absorption of O2(Δg) in the crystalline phases of oxygen

Three luminescence bands in the yellow and red spectral region, which are related to the ¹Δ_g¹Δ_g→³Σ_g^{− 3}Σ_g⁻ double electronic transition of O₂, have been investigated in the , β, and γ phase of solid oxygen. The temperature dependence of the intensity of the yellow band is strongly influenced by emission from higher vibrational levels of O₂(¹Δ_g), which are populated by anharmonic V–V pumping. The broken mirror symmetry of the luminescence and absorption bands in the phase of solid O₂ points to an interaction between the electrons and the elementary excitations of the crystal, which is different in the ground and excited electronic states, e.g., a quadratic electron–phonon interaction.     

Surface properties of Si from photoelectric emission at room temperature and 80 °K

The position of the Fermi level with respect to the energy bands at a semiconductor surface as well as changes in the work function can be determined from the energy distributions of photoelectrically emitted electrons. Prior studies involved the photoelectric yield spectrum and required assumptions concerning the photoelectric threshold; the present method is free of such assumptions. Measurements at room temperature indicate that the Fermi level lies 0.23 eV and 0.41 eV above the top of the valence band for degenerate p and n-type materials, respectively. These results confirm those of Allen and Gobeli¹). Cooling to 80 °K increases the work function of p-type material by 0.025 eV while that of n-type Si remains unchanged; the results show that the electron and hole gases in the surface states are degenerate. The density of surface states lies between 7 × 10¹³ and 10¹⁵ eV⁻¹ cm⁻². On the cesiated surface, the Fermi level lies 0.16 eV below the conduction band at room temperature and coincides with its bottom at 80 °K.     

Ion-induced secondary electron and negative ion emission from Mo/O

Absolute yields of secondary electrons and negative ions resulting from collisions of Na⁺ with Mo(100) and a polycrystalline molybdenum surface have been measured as a function of the oxygen coverage of the surface for impact energies below 500 eV. The sputtered negative ions have been identified with mass spectroscopy, and O⁻ is found to be the dominant sputtered negative ion for the surfaces at all oxygen coverages and impact energies. Both the electron and O⁻ yields have an impact energy threshold at about 50 eV and exhibit a strong dependence on oxygen coverage. The kinetic energy distributions of the secondary electrons and sputtered O⁻ were determined as functions of the oxygen coverage and impact energy. The distributions for O⁻ are characterized by a narrow low-energy peak (at 1–2 eV) followed by a low-level high-energy tail. The secondary electrons have a narrow (FWHM 1–2 eV) kinetic energy distribution, centered approximately at 1–2 eV. The shapes of the distributions and their most probable energies are essentially invariant with impact energy, oxygen coverage and the nature of the Mo surface. The emission is explained and analyzed in terms of a simple model which involves a collision-induced electronic excitation of the MoO⁻ surface state. The decay of this excited state leads to the production of both secondary electrons and O⁻ with energy distributions and yields comparable to those observed.     

上转换纳米粒子CaF2:Er3+,Yb3+的合成及其温敏特性

采用水热合成法制备了CaF₂：Yb³⁺,Er³⁺上转换纳米粒子。在980 nm激发下,研究了来源于Er³⁺的²H_11/2/⁴S_3/2→⁴I_15/2跃迁的绿光发射和来源于⁴F_9/2→⁴I_15/2跃迁的红光发射。由于Er³⁺具有一对热耦合能级（²H_11/2/⁴S_3/2）,所合成的样品在293~573 K温度范围内有良好的温敏特性。利用荧光强度比（FIR）技术,测得样品在483 K时具有最大灵敏度0.002 85 K^-1。     

147Pm激发的ZnS：Cu,Cl发光粉的研究

以高纯ZnS粉末为基质,采用高温转相、扩散,以及表面涂敷工艺,制得了¹⁴⁷Pm激发的ZnS:Cu,Cl发光粉。分析了ZnS:Cu,Cl的晶体结构,测量了ZnS:Cu,Cl的激发光谱、发射光谱、发光亮度。其晶体结构主要是六方纤锌矿型结构,激发光谱峰值波长为341nm,发射光谱峰值波长为513nm,初始发光亮度达到312mcd/m₂。由激发光谱的峰值波长341nm推算得到六方ZnS晶体的禁带宽度为3.64eV。分析了¹⁴⁷Pm激发的ZnS:Cu,Cl发光粉的发光寿命,其发光寿命达到5年以上。还探讨了该放射性发光粉的发光机理。¹⁴⁷Pm激发的ZnS:Cu,Cl的稳定发光,实际上是激发过程与复合过程的准平衡。ZnS:Cu,Cl的绿色发光来源于深施主-深受主对的复合发射。实验结果的分析表明,ZnS:Cu,Cl中深施主-深受主之间的能级间隔约为2.42eV。     

重离子冷却储存环CSRm双电子复合实验研究类锂36,40Ar15+离子同位素移动

配备电子冷却装置的重离子储存环为开展高电荷态离子的双电子复合（dielectronic recombination,DR）精密谱学研究提供了绝佳的实验平台。本工作在兰州重离子加速器冷却储存环主环（HIRFL-CSRm）上开展了类锂36,40Ar15+离子的双电子复合实验,实验观测了电子-离子质心系能量范围为0~35 eV的双电子复合速率系数谱。通过外推法获得了36,40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2的跃迁能量。同时利用GRASP2K程序理论计算了36,40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2跃迁的质量移动因子和场移动因子,进而得到双电子复合谱的同位素移动值。36,40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2同位素移动分别为0.861 meV和0.868 meV。它们均小于目前CSRm上双电子复合实验的实验分辨为~10 meV,进而解释了实验测量的DR谱上未能观察到同位素移动的原因。然而,高电荷态离子的同位素移动场效应与原子序数Z5成正比,因此,在重离子加速器冷却储存环实验环（HIRFL-CSRe）以及未来大型加速器--强流重离子加速器装置（HIAF）上有望通过DR精密谱学方法研究高电荷态重离子甚至放射性离子的同位素移动,进而获得相关原子核的核电荷半径等信息。The cooler storage ring is equipped with an electron-cooler. It is an excellent experimental platform for dielectronic recombination (DR) experiment of highly-charged ions. In this paper, the dielectronic recombination experiments of lithium-like Ar15+ ions with mass number 36 and 40 are conducted at the HIRFL-CSRm(main ring of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou). The experimental electron-ion collision energy scale is from 0 eV to 35 eV. Extrapolation method is exploited to obtain the excitation energies of transitions 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 of the 36,40Ar15+ ions from experimental data. Meanwhile, GRASP2K program is utilized to calculate the mass shift factors and field shift factors of 36,40Ar15+ ions for 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 transitions to obtain isotope shifts in DR spectra. In theoretical calculation, isotope shifts of 36,40Ar15+ ions corresponding to 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 are 0.861 meV and 0.868 meV, respectively. They are both less than the experimental precision (~10 meV) of these dielectronic recombination experiments at the CSRm, which explains that isotope shifts cannot be distinguished from the experimental dielectronic recombination spectra. However, the field shift of highly-charged ions is proportional to Z5. In the future, the dielectronic recombination experiments of highly-charged heavy ions even radioactive ions will be conducted at the HIRFL-CSRe (experimental ring of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou) and the future large accelerator facility--HIAF(High intensity Heavy-ion Accelerator Facility) to measure isotope shifts to obtain the nuclear charge radius information.     

Time-resolved luminescence of complex wide-gap oxide crystals under inner-shell excitation

In order to investigate the soft X-ray energy transformation in oxide detectors the optical spectra of several wide-gap oxide crystals were analyzed. The time-resolved luminescence (2.5–10.5 eV) and luminescence excitation spectra (50–200 and 500–630 eV) as well as decay kinetics of luminescence at 10 and 295 K were recorded using the synchrotron radiation from BW3 channel (HASYLAB, DESY). Several analogous features were discovered in the excitation spectra of both intrinsic self-trapped exciton luminescence and recombination luminescence for BeO, BeAl₂O₄, Be₂SiO₄ and AlPO₄ crystals under inner-shell excitation. Simultaneously, the excitation of Ce³⁺-luminescence in scintillating Be₂La₂O₅-Ce crystals significantly differs.     

Conversion of VUV to UV and visible in K5Li2LnF10 containing rare-earth from cerium group (Ln=La, Ce, Pr, Nd)

The potential of single crystals K₅Li₂LnF₁₀, for applications as VUV excited phosphors has been examined. The crystals were doped with lanthanide ions (Ce³⁺–Nd³⁺) with concentrations up to 100 at%. The self-quenching of luminescence is strongly reduced in this material. Luminescence spectra in the 50,000–10,000 cm⁻¹ range and excitation spectra in the 40,000–250,000 cm⁻¹ spectral range have been recorded at room and low temperature. Intense visible emission has been observed for Nd³⁺ and Pr³⁺. For the Pr³⁺ ions strong the ¹S₀–¹I₆ transition has been recorded only for concentrated crystals. Efficient conversion of VUV excitation to UV–VIS emission was observed in crystals doped with 3 and 100 at% of cerium. In both cerium-activated crystals the lifetimes of f–d transitions were equal to 32 ns.     

双波长Pr3+掺杂12CaO·7Al2O3的光存储特性

采用化学共沉淀法制备了Pr3+掺杂的12CaO·7Al2O3(C12A7:Pr3+)材料.通过X射线衍射(XRD)、发射光谱、激发光谱、余辉衰减曲线、热释发光及光激励发光等测试手段系统研究了C12A7:Pr3+材料的微观结构和光学性质.结果表明,C12A7是一种理想的适合Pr3+掺杂的基质材料,C12A7:Pr3+具有...     

热退火对SiO2：Er薄膜发光特性的影响

利用离子注入法制备SiO₂:Er样品,并在不同温度下进行退火处理。通过微区拉曼光谱、吸收光谱、X射线光电子能谱等手段对其进行结构表征,并进行了室温和变温的光致发光特性研究,得到了可见区和红外区的光致发光。其中,⁴S_3/2→⁴I_15/2的发光强度随温度的升高,先增强后减弱,呈现出反常的温度淬灭效应,此现象是由Er³⁺与SiO₂的缺陷之间的能量传递造成的。     

The optical properties of Be,Mg and Zn-diffused gallium phosphide

Interest in the Ga-site acceptors Be and Mg was stimulated by the possibility that they might produce efficient luminescence on association with O, analogous to the well-known red Zn-O luminescence in GaP but at higher transition energy. Attention was directed to diffusion doping by Be and Mg of GaP O-doped during growth because the reactivity of Be and Mg with O renders double doping during crystal growth very difficult. Structured green donor-acceptor pair spectra were observed at 1.6°K from many Be-diffused crystals, yielding an accurate measure of (E_A)_BE, 50 ± 1 meV. Moderately efficient orange-red luminescence was also observed below ∼ 100 °K from these crystals, but the intensity of this luminescence decreased rapidly to negligible levels by ∼ 200°K. This luminescence also contains sharp structure at 1.6°K, of a form characteristic of the decay of excitons bound to complex centres. Many sharp phonon replicas occur, involving local modes as well as characteristic GaP modes. One set of no-phonon lines, at least, near 2.19 eV, shows zero-field splitting, luminescence decay times and behaviour in magnetic and external strain fields characteristic of exciton decay at a centre with <100>; or <111>-type symmetry axes, containing no extra electronic particles. The exciton state is split by 2.4 meV by J-J coupling, and the axial field of the centre splits the hole states by ∼ 1.0 meV. These bound excitons are specifically characteristics of diffused GaP and appear analogous to bound excitons observed below 2.12 eV in Zn-diffused GaP. It is probable that the relevant centres contain diffusion components such as Be or Zn interstitials and improbable that O_P is involved. By contrast, weak orange bound exciton luminescence observed in Mg-diffused GaP does involve O, presumably as O_P. No analysis of the magneto-optical behaviour of this Mg-related bound exciton was possible in our crystals, so its symmetry axis was not established. It is possible that this is the Mg_Ga-O_P bound exciton. If so, the two-fold reductions in the exciton localisation energy from ∼ 0.32 eV to ∼ 0.15 eV and in the mass of the Ga-site substituent has produced dramatic changes in the form of the phonon cooperation between the Zn-O and “Mg-O” excitons. The “Mg-O” exciton luminescence is not dominant in our crystals, even at low temperature. The exciton state is again split by a local crystal field as well as by J-J coupling, but here the former splitting is predominant; 2_∈0 = 3.9 meV, Δ = 0.60 meV.     

Luminescent properties of Ce in MSO4 (M: Ca, Sr and Ba) and the effect of Na co-doping

The optical properties of Ce³⁺ in CaSO₄, SrSO₄ and BaSO₄ are reported. The Ce³⁺ ion shows 4f⁰5d¹→²F_5/2,²F_7/2 luminescence in all three sulphates. Co-doping with Na⁺ does not change the local surrounding of the Ce³⁺ ion, but enhances the amount of Ce³⁺ ions built in. Under optical excitation, besides the typical Ce³⁺ doublet emission in the ultraviolet spectral region, band emission around 445 nm was observed. This band emission was not assigned to emission from a Ce³⁺ centre, but to emission from an impurity-trapped exciton. Under X-ray excitation, both Ce³⁺ emission and an emission band around 380 nm was observed. This band was assigned to emission from a self-trapped exciton.     

New efficient mechanism of excitation of electroluminescence from erbium ions in crystalline silicon

In p–n junctions based on c-Si : Er we have realized highly efficient excitation of erbium electroluminescence at 1.54 μm with an efficiency close to unity. A possible mechanism is Auger recombination of electrons occupying the upper subband of the conduction band with free holes in the valence band whereas the energy of the recombination process is transferred by Coulomb interaction to 4f-electrons of an erbium ion transmitting it to the second excited state ⁴I_11/2 (excitation energy 1.26 eV). The observed three-level excitation of erbium ions is promising for development of a Si : Er laser.     

Photoluminescence of germanium near the screening ionization limit of excitons

Photoluminescence spectra from highly excited germanium at 25–30 K are presented. The density of free electrons and holes is determined from induced free carrier absorption and achieved values up to 10¹⁷ cm^-3. At such densities the electron-hole system is pumped to well above the screening ionization limit of excitons. The band-to-band luminescence. however, is strongly Coulomb enhanced. The spectral shape of the measured luminescence fits well with calculations based on a Yukawa interaction potential.