【作者】 林海；

【导师】 刘景和； Mauro Tonelli；

【作者基本信息】 长春理工大学 ， 材料物理与化学， 2011， 博士

【摘要】 钨酸钆钠（NaGd（WO4）2,简称：NGW）晶体是一种新型的激光基质材料,具有吸收峰宽、荧光寿命长、阈值低、增益大、效率高、热效应小等优点。该晶体可掺入较高浓度的稀土离子,因此增益介质可做成微片,这对实现半导体激光二极管（LD）泵浦的固体激光器的集成化、小型化将具有十分重要的意义。在NGW晶体中掺入Nd3+、Yb3+等稀土离子可实现1μm波段激光输出。而以Ho3+或Tm3+作为2μm波段激活离子,以Yb3+作为敏化离子,利用NGW晶体优异的物理化学性能,通过Ho3+ （Tm3+）与Yb3+间能量转移,可实现2μm激光输出,既降低了激光振荡阂值,又提高了输出效率,具有人眼安全、大气传输特性好等优点。1.采用中频感应加热提拉法,生长了NGW晶体。通过XRD分析,验证了晶体属于四方晶系、I41/a空间群,并计算了晶胞参数。测试了的TG-DTA曲线。由DTA曲线确定了晶体的熔点,通过TG曲线表明晶体在熔点以下的热稳定性很好,适合采用提拉法生长。测试了晶体的红外光谱和拉曼光谱,对振动模式进行了归属。2.采用中频感应加热提拉法,生长了Nd:NGW激光晶体。讨论了晶体的散射颗粒、生长条纹、包裹物、位错等缺陷的形貌,分析了其产生原因。比较了不同掺杂浓度的吸收光谱,随着Nd3+掺杂浓度的提高,吸收线宽无明显变化,但是吸收截面明显变大。不同掺杂Nd3+浓度样品的吸收谱形状基本一样,未出现畸变结构,说明能级间相对位置没有变化,单个离子的格位情况基本没有变化。吸收光谱表明,在400nm到900nm范围内存在一系列的吸收峰,在805nm、753nm、586nm附近的吸收峰较强、较宽,有利于LD泵浦。荧光光谱表明,晶体的最强的发射波长为1058.6nm,对应于4F3/2→4I11/2能级跃迁,另一个较弱的荧光发射波长为1334.2nm,对应于4F3/2→4I13/2能级跃迁,最弱的发射峰波长为896.5nm,对应于4F3/2→4I9/2能级跃迁。并计算了光谱参数。研究了晶体的激光性能,测试结果表明,LD泵浦的Nd:NGW激光器的激光波长在1060 nm附近,而且吸收带宽较宽,正好与泵浦源相匹配。3.采用中频感应加热提拉法,生长了Yb:NGW激光晶体。比较了不同掺杂浓度的吸收光谱,晶体中吸收截面随着掺杂浓度的增大而减小。分析得出,随着掺杂浓度的增大,掺杂离子间的距离逐渐减小,当小于1-2nm时,将发生离子间的交叉弛豫,导致基态离子对970nm光子的吸收减少。晶体吸收光谱在932nm、968nm附近有较强、较宽的吸收峰,有利于用LD泵浦。荧光光谱表明,晶体发射波长为1010nm,对应于2F5/2₂I7/2能级跃迁。并计算了光谱参数。4.采用中频感应加热提拉法,生长了Ho,Yb:NGW激光晶体。晶体吸收光谱yb3+在933nm和978nm处存在吸收峰,在978nm处吸收峰较强,半峰宽为13nm,适合采用LD泵浦,并对Ho3+、Yb3+吸收峰对应的激发态进行了归属。晶体的荧光光谱在1959nm、1998nm、2043nm有较强的发射峰,其中最强峰的发射波长为2043nm,是Ho3+的主要发射波长。发射截面积为σe=1.82×10-20cm2。晶体的上转换性能研究表明,在546nm、648nm附近出现了上转换绿光和红光的吸收峰,并研究了晶体的上转换机制,指出了相应的跃迁通道。5.采用中频感应加热提拉法,生长了Tm,Yb:NGW激光晶体。吸收光谱在965nm处有较强的吸收峰,表明这种掺杂方式有利于Yb3+对泵浦光的高效率吸收。荧光光谱表明,Yb3+发射主峰在1031nm附近,发射线宽（FWHM）达15nm,Tm3+的荧光发射波长在1679nm-1842nm范围内,发射主峰1772nm处的半高宽为72 nm左右。晶体的上转换性能研究表明,在476nm,650 nm处得到了上转换蓝光和红光,并研究了晶体的上转换机制,指出了相应的跃迁通道。更多还原

【Abstract】 The NaGd(WO4)2 crystal, short for NGW, is a new laser host material, which has several merits, such as wide absorption peaks, longer fluorescent lifetime, lower threshold value, larger gain, higher efficiency, little thermal effect and so on. The NGW gain medium can be made microchip since high concentration doping can be achieved in this crystal, which has more significance for achieving integration, miniaturization and compact structure of solid lasers pumped by laser diode.The laser emission around 1μm can be achieved through doping some rare earth ions into NGW crystal, such as Nd3+, Yb3+ and so on. Meanwhile, NGW crystal has excellent physical and chemical properties. Ho3+ or Tm3+ serves as activation ions around 2μm, and Yb3+ serves as sensitization ion. The laser emission around 2μm can be achieved through energy transfer between Ho3+(Tm3+) and Yb3+ ions, which reduce laser threshold value and enhance laser output efficiency. It has several merits, such eye safe, well atmospheric transmission characteristic and so on.1. The NGW crystal was grown by the Czochralski method. The crystals belong to tetragonal system with I4I/a space group by XRD analysis, which has a structure of scheelite. The cell parameters of crystal were calculated. The TG-DTA results of crystal indicates that the thermal stability is excellent. It is suitable to be grown by Cz method. The melting points of crystal was obtained from TG-DTA curves. The infrared and raman spectra of crystal were measured, and vibration modes of crystal were assigned.2. The Nd:NGW crystal was grown by the Czochralski method. The morphology of some defects was dicussed, such as growth stripes and wraps and so on. The reasons of defect formation were analyzed. Absorption spectra lines of different doping concentration of Nd3+ion are the same without distortion structure, which indicates the relative position of energy levels and position situation of single ion have no changes.It can be seen from absorption spectra of Nd:NGW, there are several absorption peaks from 400nm to 900nm, and the absorption peaks at around 805nm,753nm,586nm are much stronger and wide, which is suitable for laser diode pumping. The strongest emission wavelength is 1058.6nm, owing to 4F3/2→4I11/2 energy transition. The second weaker emission wavelength is 1334.2nm, owing to 4F3/2→4I13/2 energy transition. The weakest emission wavelength is 896.5nm, owing to 4F3/2→4I9/2 energy transition. The spectral parameters of crystal were also calculated.The laser performance of Nd:NGW crystal were measured. It can be seen from testing results that laser output wavelength is about 1060 nm for Nd:NGW laser, which can be suitable for LD pumping.3. The Yb:NGW crystal was grown by the Czochralski method. As for Yb:NGW crystal, absorption cross section decreases with doping concentration of Yb3+ ion. The reason is that distance to doping concentration decrease gradually with doping concentration increasing. The cross relaxation will happen When ions distance is enough small, which lead to weak absorption to 970nm photons.From absorption spectra of Yb:NGW crystal, the absorption peaks at around 932nm, 968nm are much stronger and wide, which is suitable for laser diode pumping. The emission wavelength of Yb:NGW crystal is 1010nm, owing to 2F5/2→2I7/2 energy transition. The spectral parameters of crystal were also calculated.4. The Ho,Yb:NGW crystal was grown by the Czochralski method. In the absorption spectrum of Ho:Yb:NGW crystal, two absorption peaks occur at 933nm and 978nm, and strongest absorption peak exists at 978nm with FWHM of 13nm, which matches well the characteristic absorption of Yb3+ ions and suitable for absorbing pumping light. The activated state related to absorption peaks of Ho3+ and Yb3+ ions were assigned. There exist stronger emission peaks at 1959nm,1998nm and 2043nm, and the strongest emission is at 2043nm, which is main emission wavelength of Ho3+ ions. The emission cross section is 1.82×10-20cm2.The upconversion fluorescent spectra of Ho,Yb:NGW were measured. The upconversion absrption peaks at around 546nm and 648nm were observed. The mechanism of upconversion for crystal was studied, and the responding transition channel was given. 5. The Tm,Yb:NGW crystal was grown by the Czochralski method. From absorption spectra of Tm,Yb:NGW crystal, the absorption peaks at around 965nm is much stronger. It is indicated that Tm,Yb:NGW crystal has higher absorption efficiency. In the Tm,Yb:NGW crystal, the main emission peak exist at 1031nm with linewidth of 15nm. The emission wavelength of Tm3+ ions is at the range of 1679nm—1842nm. The FWHM of main emission peak at 1772nm is about 72 nm.The upconversion fluorescent spectra of Tm,Yb:NGW were measured. There exist upconversion blue and red absrption peaks at around 476nm and 650 nm. The mechanism of upconversion for crystal was studied, and the responding transition channel was given.更多还原