Color centers and charge state recharge in gamma-irradiated Yb : YAP

Gamma-ray irradiation induced color centers and charge state recharge of impurity and doped ion in 10 at.% Yb:YAP have been studied. The change in the additional absorption (AA) spectra is mainly related to the charge exchange of the impurity Fe2+, Fe3+ and Yb3+ ions. Two impurity color center bands at 255 and 313 nm were attributed to Fe3+ and Fe2+ ions, respectively. The broad AA band centered at 385 nm may be associated with the cation vacancies and F-type center. The transition Yb3+ -> Yb2+ takes place in the process of gamma-irradiation. Oxygen annealing and gamma-ray irradiation lead to an opposite effect on the absorption properties of the Yb:YAP crystal. In the air annealing process, the transition Fe2+ -> Fe3+ and Yb2+ -> Yb3+ take place and the color centers responsible for the 385 nm band was destroyed. (c) 2005 Elsevier B.V. All rights reserved.

Spectra analysis of a novel Ti-doped LiAlO2 single crystal

LiAlO2 single crystals doped with Ti at concentration 0.2 at.% are grown by the Czochralskl technique with dimensions Phi 42 x 55 mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO2 and Ti: LiAlO2. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600-800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the V-Li and V-O absorptions, respectively. The peaks at 716nm and 798nm may stem from the V-Li(+) and F+ absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti4+-doping produces more lithium vacancies in the LiAlO2 crystal. The intensities of [LiO4] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO2 crystals.

Single crystal beta-Ga2O3: Cr grown by floating zone technique and its optical properties

beta-Ga2O3: Cr single crystals were grown by floating zone technique. Absorption spectra and fluorescence spectra were measured at room temperature. The values of field splitting parameter Dq and Racah parameter B were obtained by the peak values of absorption spectra. The value 10Dq/B=23.14 manifests that in beta-Ga2O3 crystals Cr3+ ions are influenced by low energy crystal field. After high temperature annealing in air, the Cr3+ intrinsic emission was enhanced and the green luminescence disappeared. The strong and broad 691 nm emission was obtained at 420 nm excitation due to the electron transition occurred from T-4(2) to (4)A(2). The studies manifest that the beta-Ga2O3 crystals have the potential application for tunable laser.

Effects of gamma-irradiation and air annealing on Yb-doped Y3Al5O12 single crystal

The effects of gamma-irradiation on the air-annealed 10 at.% Yb:Y3Al5O12 (YAG) and air annealing on the gamma-irradiated 10at.% Yb:YAG have been studied by the difference absorption spectra before and after treatment. The gamma-irradiation and air annealing led to opposite changes of the absorption properties of the Yb:YAG crystal. After air annealing, the gamma-irradiation induced centers were totally removed and the concentration of Fe3+ and Yb3+ were lightly increased. For the first time, the gamma-irradiation induced valence changes between Yb3+ and Yb2+ ions in Yb:YAG crystals have been observed. (C) 2007 Elsevier B.V. All rights reserved.

内蒙古克氏针茅草原土壤呼吸作用研究

土壤呼吸是陆地生态系统碳循环中的重要环节，是土壤与大气之间碳交换的主要输出途径。草地生态系统土壤呼吸作用研究在全球碳循环研究中占有十分重要的地位和作用。本研究选取我国内蒙古锡林郭勒盟典型草原区内的克氏针茅草原作为研究对象，基于Li-6400-09便携式土壤呼吸观测系统2005年生长季的野外观测资料，研究了克氏针茅草原土壤呼吸速率的日、生长季动态及其影响因子。研究结果表明： (1)　2005年生长季，克氏针茅草原土壤呼吸速率的日、生长季动态均呈单峰型曲线变化;日最大值和最小值分别出现在10:0013:00和凌晨4:00左右;生长季日均最大值(0.14mgCO2m-2s-1)出现在6月份，日均最小值(0.03mgCO2m-2s-1)出现在8月份。与以往典型草原土壤呼吸研究相比，峰值和最低值出现时间均提前。 (2)　在日尺度上，随着生长期的变化，控制土壤呼吸变化的环境因子有所不同。其中生长季初期和末期土壤呼吸速率日动态的限制因子主要为总辐射，而生长季中期，控制因子为气温和土壤含水量(010cm、1020cm)。在整个生长季的尺度上，影响土壤呼吸动态的环境因子主要为土壤含水量(010cm、1020cm、2030cm)、总辐射和土壤温度(10cm、15cm、20cm)，其协同作用可解释土壤呼吸变化的92%。其中约有72％的土壤呼吸作用变异是由表层土壤含水量(010cm、1020cm)和总辐射共同决定的，而010cm土壤含水量可单独解释土壤呼吸生长季变异的51%。 (3)　克氏针茅草原地上生物量的生长季变化呈单峰曲线型，8月份达到峰值。地下生物量和总生物量(地上和地下之和)在整个生长季的变化比较平缓，但在6月份和9月份分别出现一个峰值。其中，地上生物量是决定同一时间不同地点土壤呼吸速率变化的主要影响因素;而地下生物量对同一地点不同时间土壤呼吸速率变化的作用更为显著。其中地下生物量可解释土壤呼吸速率在整个生长季变异的25％。 (4)　通过灰色关联度方法综合分析环境因子与生物因子(地上和地下生物量)得到各影响因子与日均土壤呼吸速率生长季变化密切程度的相对顺序：0~10cm土壤含水量>地下生物量>10~20cm土壤含水量>20~30cm土壤含水量>气温>20cm土壤温度>5cm土壤温度>15cm土壤温度>10cm土壤温度>地上生物量>总辐射。结果表明：在2005年生长季，土壤含水量(0~10cm)是控制克氏针茅草原日均土壤呼吸速率生长季变化的主导影响因素，其次是植被的地下生物量。气温与土壤呼吸生长季变化的密切程度大于各层土壤温度。而地上生物量和总辐射对日均土壤呼吸生长季变化的影响最弱。

太行花属（Taihangia Yu et Li）种质资源的研究

本文报道了太行花属（Taihangia Yu et Li）的种群分布、生物学特性和离体培养的初步结果。 太行花种群由于环境和生物等方面的原因仅在太行山区有狭小分布。来源于不同地区种群的太行花其形态特征具有丰富的表型，在引种条件下更为显著。而酯酶同工酶和过氧化物酶同工酶分析进一步证实了其遗传的稳定性和同源性。 实验表明，太行花在北纬39°58'，最低温度-11℃的北京北京植物园，露地越冬正常。温度提高至40℃时生长发育受抑制而迟滞，以25℃最为适宜，增殖率最高。太行花对土壤的适应范围较广，在泥炭培养土上移殖的幼苗成活率达97.20%，主根须根发达，叶生长良好。不同强度光照处理12000Lux效果最好。 太行花生育期为230多天，生长积温为3763℃左右。物候期受环境条件和当年气候的影响，不同种群和个体之间有一定的差异。花的性别、花期和开花量等与纬度、海拔主要与温湿度相关。 太行花的茎尖、花芽、花梗、萼片、花瓣和叶子等外植体均能在MS附加不同种类和浓度植物激素的培养基中分化，其分化途径和分化效果因附加成分、外植体类别而异。在含有0.1mg/L IAA和0.5mg/L 6-BA的培养基中，不但能启动花芽正常生长、开花、形成合子胚，而且也能诱导花芽、花梗、茎尖产生花芽和营养芽。在芽的继代培养中，细胞分裂素能大量诱导芽的分化，最好的配比是0.5mg/L 6-BA、0.1mg/L ZJ;只含生长素时可以诱导生根或脱分化，其中生根最好的是0.5mg/L IAA;2.4-D单独使用时，能较好地使花芽、叶等脱分化，其最佳浓度为1.0mg/L。