稀土掺杂透明磷酸盐玻璃陶瓷的制备与发光特性研究

【作者】 于晓晨；

【导师】 宋峰； 孙同庆；

【作者基本信息】 南开大学 ， 凝聚态物理， 2009， 博士

【摘要】 Er³⁺和Er³⁺/Yb³⁺掺杂磷酸盐玻璃具有对Er³⁺离子溶解度较高、Er³⁺离子在磷酸盐玻璃中受激发射截面较大、荧光寿命长、声子能量适中、不易发生荧光淬灭、Er³⁺/Yb³⁺间能量传递效率高、上转换强度较弱等优点,因而近年来,作为1.5μm微片激光器和光纤激光器与放大器的良好基质材料,而受到了极大地关注。这些器件在光纤通信、激光测距、相干光学传输等方面有重要的应用。但是,磷酸盐玻璃存在化学和机械稳定性稍差、热导性和软化温度也不如硅酸盐玻璃等缺点,因而在光学性能上和实际应用上也受到一些限制。近来出现了一种新型激光介质材料——稀土离子掺杂的透明玻璃陶瓷,通过调整组分和热处理条件,可以实现对玻璃网络结构和玻璃化能力的调节,达到析晶可控和稀土在纳米晶相中重掺的目的。它兼备晶体和玻璃的一些优点,具有高发光效率、高透过率、高稳定性和发光波段可调等性能。而且其热导性和耐热冲击性比较好,使之更适合用做大功率激光工作物质。为了结合磷酸盐玻璃和玻璃陶瓷的双重优点,我们采用高温熔融法,通过合理设计配比,制备出了一系列Er³⁺/Yb³⁺掺杂的透明磷酸盐玻璃陶瓷,应用差热分析（DTA）、x射线衍射（XRD）、透射电镜（TEM）或扫描电镜（SEM）、光致发光谱（PL）以及Judd-Ofelt（J-O）理论、McCumber理论和Fuchtbauer-Ladenburg（F-L）方程等手段和方法,详细研究了各组分和热处理制度对玻璃陶瓷的相组成、微观结构以及发光性能的影响,取得了一些重要的结论和创新性成果,为稀土掺杂透明磷酸盐玻璃陶瓷的进一步发展和应用奠定了基础。主要的研究工作和创新性成果有:制备了摩尔组分为37P₂O₅-31.4CaO-25.6Na₂O-6Al₂O₃-0.25Er₂O₃-7.5Yb₂O₃的磷酸盐玻璃陶瓷,研究了Er³⁺离子在玻璃和玻璃陶瓷中的发光特性。XRD测试表明,玻璃陶瓷中的晶体颗粒组成为YbPO₄和ErPO₄,晶粒尺寸和析晶速率都随着热处理时间的延长而逐渐增加。通过PL谱测量发现,与玻璃相比,Er³⁺离子在玻璃陶瓷中的上转换发光强度和1.5μm近红外发光强度显著增大,这与析晶度和纳米晶粒尺寸的变化规律比较吻合。应用J-O理论、McCumber理论和F-L方程较完整地计算、评价了玻璃晶化前后的光谱学参数。确认由于晶化热处理后Er³⁺离子进入到YbPO₄晶格,提高了其配位对称性和有序性,降低了其所处格位的共价性,导致其Ω₂显著减小,从而显著提高了其上转换发光性能以及1.5μm近红外发光效率、有效宽度和增益参数等。我们还测量了上述玻璃陶瓷在不同温度下的上转换和近红外发光特性,利用Er³⁺/Yb³⁺双掺系统的能级结构和跃迁过程分析了发射强度随温度的变化规律,以及用多声子弛豫（MPR）理论分析了Er³⁺离子⁴I_13/2能级的寿命随温度升高而降低的原因。这些结果对进一步优化激光器和高增益光纤器件材料有一定的指导作用。制备并研究了Ce³⁺/Er³⁺/Yb³⁺掺杂的透明磷酸盐玻璃陶瓷的发光特性。发现引入Ce³⁺后,通过Er³⁺和Ce³⁺之间的能量传递(Er³⁺:⁴I_11/2+Ce³⁺:²F_5/2→Er³⁺:⁴I_13/2+Ce³⁺:²F_7/2),可以加快Er³⁺离子从⁴I_11/2到⁴I_13/2能级的无辐射跃迁速率,从而有效抑制975nm激光二极管（LD）抽运下的磷酸盐玻璃陶瓷中的可见上转换发光,改善Er³⁺在1.5μm附近波段的发光性能,使Ce³⁺/Er³⁺/Yb³⁺掺杂的透明磷酸盐玻璃陶瓷更适合作为光纤放大器和激光器的增益介质材料。制备了含有LiPO₃单相和LiPO₃与TiP₂O₇复合相的透明发光玻璃陶瓷,确定了热处理条件对Er³⁺/Yb³⁺共掺磷酸盐玻璃的晶粒尺寸、透光率、上转换发光以及1.5μm近红外发光性能的影响,为进一步研究该类稀土掺杂透明磷酸盐玻璃陶瓷提供了依据。晶化后,玻璃陶瓷中的上转换发光明显增强,并随着热处理温度的升高或时间的延长进一步增加。纳米晶的析出对Er³⁺离子在1.5μm处的近红外发光也有积极的影响,其发射峰出现了一定的Stark劈裂,谱线也有所加宽。由光谱性质测试和对光学性能参数的计算表明,该类玻璃陶瓷与同组分玻璃相比,具有更宽的1.5μm的发射带宽,更强的1.5μm近红外发光强度和上转换发光强度。其1.5μm近红外荧光的品质因数σ_e×τ_mea和增益参数σ_e×Δλ_eff均优于ZBLAN玻璃。例如480℃热处理4h样品GCA的品质因数和增益参数与ZBLAN玻璃相比,分别增加近33%和22%。更多还原

【Abstract】 In recent years, Er³⁺ and Er³⁺/Yb³⁺ co-doped phosphate glasses have attracted much attention as host materials for microchip lasers and fiber lasers and amplifiers operating at the eye-safe wavelengths of 1.54μm. They have wide applications including optical communication, range finding, coherent optical transmission and etc. The co-doped glasses exhibit high solubility of rare earth ions, large stimulated emission cross-section, long radiative lifetime, high energy transfer efficiency from Yb³⁺ to Er³⁺, and weak interaction among active ions.Unfortunately, their relatively poor thermal and chemical durability prevents them from optical properties and widely practical applications. Recently, rare earth （RE） doped transparent glass ceramics （TGC） have been investigated as laser materials since they exhibit high luminescent efficiency, Vis-NIR transparency, chemical stability, and so on. Such glass ceramics are characterized with their adjustable structure, controllable phase crystallizing and heavy RE³⁺-doping level. More importantly, the glass ceramics have better properties of thermal conductivity and thermal shock, which make them more suitable to be laser materials for high-power devices. In order to combine the good performance of the erbium doped phosphate glass and the nanostructure of glass ceramic, we fabricated Er³⁺/Yb³⁺ co-doped phosphate glass ceramics by the high-temperature melting technique. Using different thermal analysis （DTA）, x-ray diffraction （XRD）, transmittance electronic microscope （TEM） or scanning electronic microscope （SEM）, photoluminescence spectra （PL）, and Judd-Ofelt （J-O） theory, McCumber theory, and Fuchtbauer-Ladenburg （F-L） formula, we studied the correlation among heat treating techniques, precipitated crystal size, crystallinity, transmittance and luminescence behaviors. A series of important conclusions and innovative results with practical significance were obtained, which provide the foundation for further development and application of RE ions doped phosphate glass ceramics.Transparent 37P₂O₅-31.4CaO-25.6Na₂O-6Al₂O₃-0.25Er₂O₃-7.5Yb₂O₃ （mol %） phosphate glass ceramics have been prepared. The spectroscopic properties of Er³⁺ in the glass and glass ceramics have been studied. XRD results indicated that the nanocrystals were YbPO₄ and ErPO₄ and the crystal size and crystallinity increased with the heat treating time increasing. The upconversion and near infrared emissions of the Er³⁺ ions in the glass ceramics are increased significantly with the precursor glass. This agrees well with the varation of the crystal size and crystallinity. Calculation using J-O theory, McCumber theory and F-L formula confirmed that Er³⁺ ions entering into the nanocrystals led to their higher ligand symmetry and weaker covalence properties than in the glass matrix, which madeΩ₂ decreased and further improved the properties of upconversion luminescence and 1.54μm near infrared emission efficiency, effective width, and gain parameters. The effect of temperature on the luminescence intensity of up-conversion and near infrared in Er³⁺/Yb³⁺ co-doped phosphate glass ceramics has been investigated. The fluorescence intensity is changing at different temperature and the results are explained with the level transitions in Er³⁺/Yb³⁺ co-doped system. Meanwhile, the lifetime of Er³⁺:⁴I_13/2 level corresponding to different operating temperature and pump power is also discussed, and the experimental results are fitted using multiphonon relaxation theory. These results will be helpful to further optimize parameters of lasers materials and high gain fiber devices.We prepared Ce³⁺/Er³⁺/Yb³⁺ tri-doped transparent phosphate glass ceramics and discussed the influence of energy acceptors Ce³⁺ ions on the upconversion and 1.5μm emission properties of Er³⁺ in the glass ceramics. The phonon-assisted energy transfer between Er³⁺ and Ce³⁺ (Er³⁺:⁴I_11/2+Ce³⁺:²F_5/2→Er³⁺:⁴I_13/2+Ce³⁺:²F_7/2) accelerated population feeding from the ⁴I_11/2 to the ⁴I_13/2 level, and therefore drastically decreased the upconversion emission of Er³⁺ under 975 nm LD excitation. Meanwhile, the near infrared luminescence enhanced greatly with the introduction of Ce³⁺ ions at the proper concentration. The Ce³⁺/Er³⁺/Yb³⁺ tri-doped phosphate glass ceramics will be preferable for efficient 980 nm pumped Er³⁺-doped optical amplifiers and lasers.Luminescence TGCs containing LiPO₃ and TiP₂O₇ have been prepared successfully. We investigated the effects of heat treatment conditions on the crystal size, Vis-NIR transparency, the upconversion and near infrared luminescence of Er³⁺ ions in the glass ceramics. The upconversion luminescence intensity of Er³⁺ ions in the glass ceramics increased significantly with increasing heat treating temperature or time under 975nm wavelength excitation. Stark split near infrared emission peaks of Er³⁺ have been observed in the glass ceramics, and the effective bandwidth increases with increasing heat treating temperature. PL spectra measurements and J-O calculation reveal that Er³⁺/Yb³⁺ co-doped TGCs have much broader 1.5μm bandwidth, much stronger 1.5um luminescence, red and green upconversion luminescence than the precursor glass. For the co-doped TGCs, both of their 1.5μm quality factors for bandwidth (σ_e×Δλ_eff) and for gain (σ_e×τ_mea) are better than ZBLAN. For the glass ceramic heat treated at 480℃for 4h, the bandwidth and gain are 1.33 and 1.22 times than that of ZBLAN, respectively.更多还原