Absorption and emission spectra of yttria-stabilized zirconia and magnesium oxide

We have investigated the luminescence and absorption spectra of doped and undoped ZrO₂-Y₂O₃ and MgO crystals at room- and low temperatures. The crystals used are partly doped with the transition metals Ni, Co, Cr and the rare earth Pr. The emission spectra were obtained under laser excitation at different wavelengths. The observed optical emission and absorption bands of the MgO crystals doped with Ni, Co and Cr correspond to transitions between spin-orbit split crystal field levels of the transition metals. Luminescence and absorption bands of undoped yttria-stabilized zirconia (YSZ) crystals are due to color centers, absorption bands of the doped YSZ correspond to the well known transitions of the Ni²⁺, Co²⁺ and Pr³⁺ ions, respectively. The emission spectra of the doped YSZ obtained under various laser excitations can be explained by an energy transfer process between the color center and the doping materials. The influence of annealing on the absorption and emission of Pr³⁺/Pr⁴⁺ is investigated.     

Geometric characterization of a singly charged oxygen vacancy on a single-crystalline MgO(001) film by electron paramagnetic resonance spectroscopy

Electron paramagnetic resonance spectra of singly charged surface oxygen vacancies (F or color centers) formed by electron bombardment on a single-crystalline MgO film under UHV conditions are reported. The embedding of the defect in a well-defined geometrical environment allows not only for the determination of the magnetic quantities but also, in conjunction with STM studies, for the geometrical assignment of the observed signal to color centers located on the edges of the MgO film.     

Investigation of the homogeneity of sol-gel-derived microcrystals with a mixed ZnO-MgO-FeO composition

The homogeneity (concentration boundary of the precipitation of the MgO phase) in sol-gelderived microcrystals with a mixed ZnO-MgO-FeO composition has been investigated using the optical and X-ray diffraction methods. It has been shown that optical spectroscopy in this case is a more sensitive method. The luminescence line of a deep center at 700 nm has been observed for the first time and used as an indication of the precipitation of the MgO phase. Based on the experimental data, the concentration boundary of the precipitation of the MgO phase is evaluated to be 4–10 at %, which is in good agreement with the available theoretical estimate.     

The orange luminescence band in MgO crystals

Nominally pure MgO crystals exhibit a bright orange luminescence when excited with u v or visible laser light This luminescence has been characterized using a variety of measurements with pulsed and cw laser sources Its amplitude increases with temperature to about 400 K. while the lifetime of emission decreases from 270 μs at 290 K to 9 μs at 433 K This emission appears to originate in hole recombination with Fe²⁺ ions Hole trapping at V^?_OH and V^?_Al centers may occur as an intermediate step Bleaching with 514 5-nm Ar⁺ laser light is reversible upon exposure to u v radiation Present data are compared with those obtained previously on the thermoluminescence of irradiated MgO crystals.     

α-Al_2O_3透明陶瓷的发光及热释光特性

采用传统无压烧结工艺,以MgO为烧结助剂,制备出了透明性良好的α-Al2O3透明多晶陶瓷,测定了其吸收光谱、荧光光谱、激发光谱,并做了热释光测试.结果表明,吸收光谱存在192nm和225—250nm吸收峰,分别对应于F色心和F+色心.在荧光光谱的410nm处发现有明显的发射峰.结合对其激发光谱的研究,证明了对应于F和F+色心.热释光谱中存在368,456,614K三个热释光峰,其中456K的峰值是受热激发的电子与F+色心复合产生的.     

Refractive Index Change and Color Center Formation in LiYF4 Crystal Induced by a Femtosecond Laser

The refractive index change and color centers formation in LiYF4 crystal at room temperature are induced by a femtosecond laser irradiation. A mechanism for refractive index change and color centers formation is proposed.     

Study of color centers produced in thulium doped YLF crystals irradiated by electron beam and femtosecond laser pulses

In this work, we report the influence of the presence of photochromic and color centers in the photobleaching of thulium ions blue emission in YLF (YLiF₄) crystals doped with 1 mol% Tm (3+). The samples were irradiated at room temperature both with electron beam and high intensity ultrashort pulses from a Ti:Sapphire CPA laser system. In both irradiations the production of photochromic and color centers was observed via the absorption bands in the UV and visible ranges. Pure LiF and pure and oxygen doped YLF crystals were used to identify the color centers produced and their optical properties. From a phenomenological model it was possible to study the interaction between color centers and thulium ions, and their effect in photobleaching and photodarkening behaviors. Finally, the blue up laser level population was computed using a rate equation analysis.     

Color center formation in soda lime glass and NaCl single crystals with femtosecond laser pulses

The high instantaneous powers associated with femtosecond lasers can color many nominally transparent materials. Although the excitations responsible for this defect formation occur on subpicosecond time scales, subsequent interactions between the resulting electronic and lattice defects complicate the evolution of color center formation and decay. These interactions must be understood in order to account for the long term behavior of coloration. In this work, we probe the evolution of color centers produced by femtosecond laser radiation in soda lime glass and single crystal sodium chloride on different time scales, from microseconds to hundreds of seconds. By using an appropriately chosen probe laser focused through the femtosecond laser spot, we can follow the changes in coloration due to individual or multiple femtosecond pulses, and follow the evolution of that coloration for a long time after femtosecond laser radiation is terminated. For the soda lime glass, the decay of color centers is well described in terms of bimolecular annihilation reactions between electron and hole centers. Similar processes appear to operate in single crystal sodium chloride. PACS 82.50.Pt; 78.55.Qr; 78.55.Fv; 78.47.+p     

Multiple filamentation of femtosecond laser pulses

The formation of fluorescent channels with color centers in LiF crystals under the action of the multiple filamentation of femtosecond laser pulses is studied experimentally and theoretically for pulse powers around four orders of magnitude higher than the critical self-focusing value.     

LiF晶体中F3^＋—F2混合色心激光器

本文报道了室温下LiF晶体中F_3~+-F_2混合色心激光器.利用一块晶体和单一泵光,输出激光波长范围从510～580nm、640～710nm.总带宽140nm.     

微波吸收法研究ZnO光电子衰减过程

微波吸收无接触测量技术可以用于半导体粉体材料、微晶材料等研究光生载流子衰减过程。本文采用微波吸收法在室温下分别测量了ZnO纳米材料和微晶材料的光电子衰减过程。发现在紫外激光短脉冲激发下,两种材料的导带光电子寿命有很大的差异,ZnO微晶粉体材料的光电子寿命为50ns,而ZnO纳米材料的光电子寿命仅为10ns。分析认为纳米ZnO的光电子寿命缩短是由于纳米ZnO晶体的表面积远远大于体材料的表面积,纳米材料的表面形成了大量的缺陷能级,加速了光电子的表面复合,缩短了光电子的寿命。纳米材料内部缺陷增多和量子限域效应同样会缩短光电子的寿命。     

A compact and high efficiency diode pumped green laser based on MgO doped PPLN

In this work, an efficient intra-cavity second harmonic generation of green laser in a periodically poled MgO doped LiNbO₃ (MgO:PPLN) bulk crystal using a compact Nd:YVO₄ laser as a fundamental laser source is reported. Different length, different working temperature MgO:PPLN crystals are tested and investigated in the SHG experiments. The maximum output power at 532 nm is 6.2 W at the absorbed pump power at 808 nm of 14 W, the optical to optical conversion efficiencies from 808 to 532 nm and 1064 to 532 nm are 43 and 77%, respectively, the instability in 2 hours is less than 5%.     

Highly nonlinear fundamental mechanisms of excitation and coloring of wide-gap crystals by intense femtosecond laser pulses

Analysis of the spatial distribution of the color centers formed in wide-gap LiF and MgF₂ crystals in a laser beam channel has shown that these centers are formed in numerous longitudinal filaments into which a laser beam splits when propagating in a medium. The luminescence of the produced color centers is photoluminescence, which is excited by the supercontinuum radiation in the filaments.     

Transversely pumped laser using F 3 + and F2 mixed color centers in a LiF crystal at room temperature

A stable laser with F₃⁺ and F₂ mixed color centers in LiF crystal is constructed using a transversely pumped cavity at room temperature. The mixed color center laser is pumped with a nitrogen-laser-pumped dye laser. A pulse output of the laser is 0.23 mJ. The pulse widths of the F₃⁺ and F₂ color center lasers are about 12 and 8.5 ns, respectively. The optical–optical conversion efficiency is about 5.0%. The divergence of the F₃⁺ color center laser beam is about 2.2 mrad and that of the F₂ color center laser beam about 3.5 mrad. The polarization of the mixed color center laser is about 0.97. The output of the F₃⁺ color center laser extends from 515 to 575 nm and peaks at 540 nm, while that of the F₂ color center laser extends from 633 to 705 nm and peaks at 667 nm.     

Laser stimulated luminescence in KCl and NaF containing color centers

A broad luminescence band was found in laser irradiated KCl and NaF crystal containing color centers. This emission extends on both sides of the laser line and is interpreted as “hot” fluorescence due to radiative retrapping of laser ionized color centers.     

A high-stability medium based on CaF<Subscript>2</Subscript>:Na crystals with colloidal color centers: I. Photothermochemical conversion of colloidal color centers in CaF<Subscript>2</Subscript>:Na crystals

Photothermochemical conversion of simple color centers (which include from one to four anionic vacancies) and highly aggregated ones in additively colored crystals of calcium fluoride doped by sodium is studied. The annealing of crystals with a low sodium content in a reducing atmosphere (additive coloration) leads to the predominant formation of simple color centers, which convert into highly aggregated centers under the joint action of heating and irradiation in absorption bands of simple centers. The irradiation of highly aggregated centers into their absorption bands and simultaneous heating causes these centers to convert into simple centers. The additive coloration of crystals with a relatively high sodium content leads to the predominant formation of highly aggregated centers. The heating of these crystals along with the irradiation in absorption bands of highly aggregated centers causes these centers to convert into simple centers. The formation of different color centers in the course of additive coloration of crystals with different impurity content and different results of photothermochemical conversion of centers in these crystals are connected with the dual action of impurities. Anion vacancies, which compensate the charge of the impurity alkali metal, facilitate the aggregation of color centers. At the same time, the alkali impurity stabilizes simple color centers.     

Reactivity of (H)(e) color centers at the MgO surface: formation of O2 and N2 radical anions

We have considered the interaction of O₂ and N₂ molecules with electrons trapped at the surface of MgO by performing embedded cluster DFT calculations. Trapped electrons at the surface of MgO react instantaneously with O₂ and N₂ leading to the formation of the corresponding O₂⁻ and N₂⁻ molecular anions stabilized at specific surface sites. So far, the atomistic model for this process was based on the idea that the electrons are trapped at oxygen vacancies, the F_S⁺ centers. Recently, it has been shown that morphological sites at the MgO surface like a reverse corner, a step or a corner, can adsorb hydrogen and stabilize (H⁺)(e⁻) pairs giving rise to a new class of paramagnetic color centers. Here we show that these centers exhibit reactivity towards O₂ and N₂, which is fully consistent with the experimental observations, providing further support to the new model of electron traps at the MgO surface.     

Color center formation in KCl and KBr single crystals with femtosecond laser pulses

Because of their extremely high instantaneous powers, femtosecond lasers can color many nominally transparent materials. Although the excitations responsible for this defect formation occur on subpicosecond time scales, subsequent interactions between the resulting electronic and lattice defects complicate the evolution of color center formation and decay. These interactions must be understood in order to account for the long-term behavior of coloration. In this work, we probe the evolution of color centers generated by femtosecond laser radiation in potassium chloride and potassium bromide single crystals on time scales from microseconds to hundreds of seconds. By using an appropriately chosen probe laser focused through the femtosecond laser spot, we follow the changes in coloration due to individual or multiple femtosecond pulses and the evolution of that coloration for long times after femtosecond laser radiation is terminated.     

Yb∶YAG晶体的荧光特性研究

测量了不同掺杂浓度Yb∶YAG晶体氧化和还原气氛退火前后的色心吸收光谱、荧光光谱和荧光寿命.研究了色心对Yb∶YAG晶体的荧光强度和荧光寿命的影响.结果表明,只有当Yb的掺杂浓度大于10 at.%时,色心吸收的加强对发光强度和荧光寿命有明显猝灭作用.     

Tunable laser radiation,nonlinear absorption,and “anti-stokes” luminescence of color centers in α-Al2O3

This work investigates the generation of laser radiation by color centers of leucosapphire, nonlinear absorption, and the excitation mechanism of UV-luminescence. It is shown that UV-luminescence from color centers, excited in the 0.68 m absorption band, is caused by a two-staged excitation mechanism. The optical characteristics of the color centers are measured and calculation is made of the variation of the absorption coefficient with laser pulse's duration.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 41–46, October, 1987.