Sr_4Al_(14)O_(25)∶RE^(3+)(RE=Eu,Ce,Tb)中稀土离子的发光性质

采用高温固相反应合成了Sr4Al14O25∶RE3+(RE=Eu,Ce,Tb)样品,研究了其中Eu3+,Ce3+和Tb3+的光谱性质,以及Ce3+与Tb3+共掺时的能量传递现象;发现Eu3+,Ce3+和Tb3+占有两个格位,与Eu2+在此基质中的情况相似;在Tb3+的发射光谱中同时观察到了来自5D3与5D4的发射,表明两能级间无辐射跃迁过程不显著;Ce3+对Tb3+有敏化作用。

通过Bi^(3+)发光特征判定“争议”格位——以Ca_2MgSi_2O_7∶Bi^(3+)荧光粉为例（英文）

在以往的研究工作中,人们经常关注给定基质具有多个格位所对应多发光中心的光致发射。取决于所掺杂的基质,多个格位的晶体化合物应该可以提供相应的多发光中心,但某些化合物有时只会表现一个发光中心,由此产生"争议性"发光中心。据以往研究,以稀土离子掺杂而为人所知的经典镁黄长石(Ca_2MgSi_2O_7)长余辉化合物具有"争议性"Ca格位。为此,在本文中以非稀土离子(Bi^(3+))特有的发光特性从侧面来研究Ca_2MgSi_2O_7化合物中的"争议性"Ca格位问题。结果表明,在250和276 nm激发波长激发下,所有的Bi^(3+)掺杂Ca_2MgSi_2O_7样品均有峰位位于582和350 nm的两个Bi^(3+)特征发射带。结合晶体结构分析,光谱结果表明,Ca_2MgSi_2O_7∶Bi^(3+)荧光粉具有对应于六配位和八配位的两个不同Ca2+格位的两个Bi^(3+)发光中心,即,Bi^(3+)(Ⅰ)(~582 nm)和Bi^(3+)(Ⅱ)(~350 nm)发光中心。此外,光谱分析进一步表明,Bi^(3+)(Ⅰ)与Bi^(3+)(Ⅱ)具有单向的能量传递,而且,发现这两个发光中心所对应的相对发射强度是依赖于激发波长和Bi^(3+)掺杂浓度。实验证明了Ca_2MgSi_2O_7晶体化合物具有两个Ca格位,而不是有些工作中所讨论的一个Ca格位。本文工作可以为已知或未知的具有"争议性"格位的晶体化合物的验证提供新的借鉴。

Investigations on Valence-Change Behaviors of Europium Ions in Eu-Doped Aluminate and Silicate Phosphors

Compounds of Sr3Al2O6 ： Eu, SrgAl14O25 ： Eu, and BaZnSiO4 ： Eu were synthesized by high-temperature solid state reactions. The doping Eu^3 ＋ ions were partially reduced to Eu^2＋ in Sr4Al14O25：Eu and BaZnSiOg：Eu prepared in an oxidizing atmosphere, N^2 ＋ O2. However, such an abnormal reduction process could not be performed in Sr3Al2O6：Eu, which was also prepared in an atmosphere of N^2 ＋ O2. Moreover, even though Sr3A1EO6：Eu was synthesized in a reducing condition CO, only part of the Eu^3 ＋ ions was reduced to Eu^2 ＋ . The existence of trivalent and divalent europium ions was confirmed by photoluminescent spectra. The different valence-change behaviors of europium ions in the hosts were attributed to the difference in host crystal structures. The higher the crystal structure stiffness, the easier the reduction process from Eu^3 ＋ to Eu^2 ＋ .

Upconversion Luminescence of Ce^(3+) Doped BK7 Glass by Femtosecond Laser Irradiation

Near-infrared to visible upconversion luminescence was observed in a multicomponent silicate （BK7） glass containing Ce^3 ＋ ions under focused infrared femtosecond laser irradiation. The emission spectra show that the upconversion luminescence comes from the 4f-5d transition of the Ce^3 ＋ ions. The relationship between the intensity of the Ce^3 ＋ emission and the pump power reveals that a three-photon absorption predominates in the conversion process from the near-infrared into the blue luminescence. The analysis of the upconversion mechanism suggests that the upconversion luminescence may come from a three-photon simultaneous absorption that leads to a population of the 5d level in which the characteristic luminescence occurs.

High Quantum Efficiency and High Concentration Erbium-Doped Silica Glasses Fabricated by Sintering Nanoporous Glasses

A new method was used to prepare erbium-doped high silica （SiO2 % 〉 96 % ） glasses by sintering nanoporous glasses. The concentration of erbium ions in high silica glasses can be considerably more than that in silica glasses prepared by using conventional methods. The fluorescence of 1532 nm has an FWHM （Full Wave at Half Maximum） of 50 nm, wider than 35 nm of EDSFA （erbium-doped silica fiber amplifer）, and hence the glass possesses potential application in broadband fiber amplifiers. The Judd-Ofelt theoretical analysis reflects that the quantum efficiency of this erbium-doped glass is about 0.78, although the erbium concentration in this glass （6 × 10^3） is about twenty times higher than that in silica glass. These excellent characteristics of Er-doped high silica glass will be conducive to its usage in optical amplifiers and microchip lasers.

A Compact Low Noise Single Frequency Linearly Polarized DBR Fiber Laser at 1550 nm

A compact low noise single frequency linearly polarized distributed Bragg reflector(DBR)fiber laser based on a 1.4-cm-long homemade Er^(3+)/Yb^(3+)-codoped phosphate single mode glass fiber has been demonstrated.An over 50 mW stable single frequency linearly polarized fiber laser was achieved.The measured slope efficiency is more than 21.6%,and the signal-to-noise ratio(SNR)is higher than 65 dB and the laser linewidth is less than 2.0 kHz.The laser RIN is measured to be less than-150 dB/Hz at the frequencies over 2.0 MHz,and the obtained linear polarization extinction ratio(LPER)is more than 30 dB.

Preparation and Fluorescent Property of Eu-Doped High Silica Glasses

A method to fabricate europium ions doped-high silica glass for transparent fluorescence materials based on the fabrication and sintering technique of nano-porous silica glass was reported. Glasses impregnated with Eu ions and sintered at above 1150 ℃ in a reduction atmosphere show a very strong blue light from an emission band at about 430 nm due to the 4f65d→4f7(8S7/2) transition of the Eu2+ ions. On the other hand, the Eu-doped glass obtained by co-impregnated with Y3+ and V5+ ions and sintering in oxidation atmosphere behaves a very strong red emission band at about 615 nm with a UV excitation. An appearance of vanadate band in the excitation spectrum of Eu3+, Y3+ and V5+ ions co-doped high silica glass implies an effective energy transferring from VO43- to Eu3+ and effective excitation of Eu3+ by about 500 nm strong broad emission of VO43-.

Transparent Ni^2＋-Doped MgO-Al2O3-SiO2 Glass Ceramics with Broadband Infrared Luminescence

We report on transparent Ni^2＋-doped MgO-Al2O3-SiO2 glass ceramics with broadband infrared luminescence. Ni^2＋-doped MgO-Al2O3-SiO2 glass is prepared by using the conventional method. After heat treatment at high temperature, MgAl2O4 crystallites are precipitated, and their average size is about 4.3 nm. No luminescence is detected in the as-prepared glass sample, while broadband infrared luminescence centred at around 1315 nm with full width at half maximum （FWHM） of about 300 nm is observed from the glass ceramics. The observed infrared emission could be attributed to the ^3T2g（^3F）→^3A2g（^3F） transition of octahedral Ni^2＋ ions in the MgAl2O4 crystallites of the transparent glass ceramics. The product of the fluorescence lifetime and the stimulated emission cross section is about 1.6×10^-24 s cm^2.

Nd^(3+) Doped Silicate Glass Photonic Crystal Fiber with Random Hole Distributions

The fabrication of one kind of large core area Nd3+ doped silicate glass photonic crystal fiber, and demonstration of the fiber's waveguidence properties were reported. This fiber owns a random air hole distribution in the cladding. The measured minimum loss of this kind of fiber is 10 dB·m-1 at 660 nm. These fibers can sustain only a single mode at least over wavelength ranging from 660 nm to 980 nm.

Spectroscopic Properties of Nd^(3+)-Doped High Silica Glass Prepared by Sintering Porous Glass

A new kind of Nd^3＋-doped high silica glass （SiO2 〉 96% （mass fraction）） was obtained by sintering porous glass impregnated with Nd^3 ＋ ions. The absorption and luminescence properties of high silica glass doped with different Nd^3 ＋ concentrations were studied. The intensity parameters Ωt （t = 2, 4, 6）, spontaneous emission probability, fluorescence lifetime, radiative quantum efficiency, fluorescence branching ratio, and stimulated emission cross section were calculated using the Judd-Ofelt theory. The optimal Nd^3＋ concentration in high silica glass was 0.27% （mole fraction） because of its high quantum efficiency and emission intensity. By comparing the spectroscopic parameters with other Nd^3 ＋- doped oxide glasses and commercial silicate glasses, the Nd^3 ＋ -doped high silica glasses are likely to be a promising material used for high power and high repetition rate lasers.

超宽带光纤放大器用的新型掺铋发光材料

最近,一种新型的掺铋发光材料引起了人们的关注。这种发光材料有长的荧光寿命(τ>200μs),在800nm激光激 发下发射波长在1200-1600nm区间的超宽带荧光(荧光半高宽FWHM>200nm),其发光性质与以往文献中报道的Bi3+或 Bi2+掺杂的发光材料的性质截然不同;光发射截面(σem)是光掺铒光纤放大器玻璃(EDFAG)的2-3倍,其σem×FWHM值是 EDFAG的10倍左右,σem×τ值是掺Ti3+蓝宝石的3倍左右。

具有超宽带近红外发光的铋激活光子玻璃

在铋掺杂的各种玻璃体系中能够产生覆盖1．2-1．6μm区间的超宽近红外发光;并对此类发光材料的发光机理进 行了初步探讨,指出铬铋共掺的锌铝硅玻璃中的宽带近红外发光源于铋而不是Cr4+离子。

掺铒高硅氧玻璃光谱性质的研究

应用Judd-Oflet理论计算了新型掺铒高硅氧玻璃中铒离子的强度参量Ωt(t=2,4,6),Ω2=8·15×10-20,Ω4=1·43×10-20,Ω6=1·22×10-20,相比于其他氧化物玻璃,表现出较大的Ω2,6值,反映了铒离子周围的近邻结构不对称性和Er-O键的离子键成分较高.利用McCumber理论计算得到了能级4I13/2→4I15/2跃迁的受激发射截面为σc=0·51pm2.这种高硅氧玻璃掺铒离子浓度尽管高于石英光纤的掺杂浓度10倍左右,其荧光寿命和量子效率仍达到6·0ms和66·0%,有可能成为新的光学放大和微片激光材料.

铈掺杂钇铝石榴石纤维的电纺丝制备及光学性能

采用静电纺丝技术制备了铈掺杂钇铝石榴石(cerium doped yttrium aluminium garnet,YAG:Ce)纳米纤维,利用扫描电镜观测了电纺丝纤维的微结构与形貌,利用荧光光谱仪表征了YAG:Ce电纺丝纤维的荧光性能。结果表明:在还原气氛下热处理制备YAG:Ce电纺丝纳米纤维时,在纳米纤维表面出现了一层直径为50～100 nm的球形凸起物。相比于空气气氛中,在还原气氛中热处理制备YAG:Ce纳米纤维的荧光发射强度显著增强。并且随着Ce^3+掺杂含量增加,YAG:Ce电纺丝纤维的荧光发射带发生红移。

空芯光子晶体光纤的研究进展

综述了空芯光子晶体光纤(HC-PCF)的原理、制作方法和最新应用进展。详细介绍了HC-PCF在粒子传输、受激拉曼散射、激光频标、单模中红外光波导和高能超短激光脉冲领域的应用,讨论了HC-PCF的发展前景。

Three-level all-fiber laser at 915 nm based on polarization-maintaining Nd^3+-doped silica fiber

Nd3+-doped fiber lasers at around 900 nm based on the 4F3/2→4I9/2 transition have obtained much research attention since they can be used as the laser sources for generating pure blue fiber lasers through the frequency doubling.Here,an all-fiber laser at 915 nm was realized by polarization-maintaining Nd3+-doped silica fiber.A net gain per unit length of up to 1.0 dB/cm at 915 nm was obtained from a 4.5 cm fiber,which to our best knowledge is the highest gain coefficient reported in this kind of silica fiber.The optical-to-optical conversion efficiency varies with the active fiber length and the reflectivity of the output fiber Bragg grating(FBG),presenting an optimal value of 5.3%at 5.1 cm fiber length and 70%reflectivity of the low reflection FBG.Additionally,the linear distributed Bragg reflector short cavity was constructed to explore its potential in realizing single-frequency 915 nm fiber laser.The measurement result of longitudinal-mode properties shows it is still multi-longitudinal mode laser operation with 40 mm laser cavity.These results indicate that the Nd3+-doped silica fiber could be used to realize all-fiber laser at 915 nm,which presents potential to be the seed source of high-power fiber laser.

Bismuth-doped germanate glass fiber fabricated by the rod-in-tube technique

Bismuth （Bi）-doped laser glasses and fiber devices have aroused wide attentions due to their unique potential to work in the new spectral range of 1 to 1.8 μm traditional laser ions, such as rare earth, cannot reach. Current Bi-dopcd silica glass fibers have to be made by modified chemical vapor deposition at a temperature higher than 2000℃. This unavoidably leads to the tremendous loss of Bi by evaporation, since the temperature is several hundred degrees Celsius higher than the Bi boiling temperature, and, therefore, trace Bi （-50 ppm） resides within the final product of silica fiber. So, the gain of such fiber is usually extremely low. One of the solutions is to make the fibers at a temperature much lower than the boiling temperature of Bi. The challenge for this is to find a lower melting point glass, which can stabilize Bi in the near infrared emission center and, meanwhile, does not lose glass transparency during fiber fabrication. None of previously reported Bi-doped multicomponent glasses can meet the prerequisite. Here, we, after hundreds of trials on optimization over glass components, activator content, melting temperature, etc., find a novel Bi-doped gallogermanate glass, which shows good tolerance to thermal impact and can accommodate a higher content of Bi. Consequently, we successfully manu- facture the germanate fiber by a rod-in-tube technique at 850℃. The fiber exhibits similar luminescence to the bulk glass, and it shows saturated absorption at 808 nm rather than 980 nm as the incident power becomes higher than 4 W. Amplified spontaneous emissions are observed upon the pumps of either 980 or 1064 nm from ger- manate fiber.