【作者】 徐东勇；

【导师】 臧竞存；

【作者基本信息】 北京工业大学 ， 无机非金属材料， 2001， 硕士

【摘要】 上转换发光现象的发现已经有了四十多年的历史，其间也有了一定的发展。但由于效率低，进一步应用和发展都受到限制。随着对全固态激光器的迫切需求，特别是作为泵浦源的大功率激光二极管的出现及迅猛发展，上转换发光材料又迎来了新的发展机遇——激光二极管泵浦上转换激光晶体实现短波长全固态激光器是十分有前途和吸引力的方案之一。文中介绍了上转换发光的发展历程及作为激光材料的最新进展情况，阐述了形成上转换发光的四种机制及影响发光强度结构方面的因素。 ZnWO₄属单斜晶系，空间群P2/c，弱晶体场，钨离子为+6价，有利于提高上转换发光强度。精心设计了温场和选择了工艺参数——轴向温度梯度△G≥30℃/cm，转速25～40转/分钟，拉速≤4mm/小时，用Czochralski法成功地生长出了具有不同掺杂浓度的光学质量的ZnWO₄单晶。通过埋在有高温相变的介质——氧化铝中退火，提高了晶体在可见光波段的透过率。密度实验结果表明掺杂的Tm³⁺离子占据了Zn²⁺离子的晶格位而生成了置换型固溶体。用电感耦合等离子体原子发射光谱法测定了Tm³⁺离子在钨酸锌中的分凝系数，约为0.27。 测量了ZnWO₄∶Tm³⁺和ZnWO₄∶Tm³⁺，Yb³⁺的吸收光谱。由于对称性低，Tm³⁺离子的³H₄能级分裂达26.7nm，所以ZnWO₄∶Tm³⁺和ZnWO₄∶Tm³⁺，Yb³⁺十分适合用808nm激光二极管激发。确定了Tm³⁺离子和Yb³⁺离子的能级分布，并计算了Tm³⁺离子的吸收截面为1.58×10^-20cm²。ZnWO₄∶Tm³⁺中，能够观测到三个上转换荧光峰，分别是对应于¹D₂→³H₆、¹G₄→³H₆和³F₃→³H₆跃迁的404、486和695nm发光，其发光强度与泵浦功率分别成1.2、0.8和1.2次方关系，其中以695nm的发光为最强。而在ZnWO₄∶Tm³⁺，Yb³⁺中，486nm发光强度增强了两个数量级以上，成为最强的发光，造成这种现象的原因是存在Yb³⁺离子向Tm³⁺离子的共振能量传递，这种敏化机制属于间接上转换敏化。双掺晶体中695、486和404nm发光与激发功率分别成1.13、1.81和2.44次方关系。经计算Tm³⁺离子的发射截面为3.99×10^-17cm²。更多还原

【Abstract】 The upconversion luminescence has been found for forty years, but it was not put into extensive use due to low efficiency. Because of urgent demand for all-solid-state lasers, especially the emergence of high power laser diode as suitable sources, the upconversion materials have attracted renewed interest as one of promising routes for achieving LD- pumped, efficient, compact long-life all-solid-state lasers emitting in visible spectral region (VSR). In the paper, the historical and recent progress of the upconversion materials is reviewed, and four mechanisms producing upconversion and the factors affecting luminescence intensity are discussed. ZnWO4 crystal belongs to monoclinic system, space group P2/c, weak crystal field intensity, which are advantageous to upconverslon. A series of different Tm3~ ion-doped concentrations ZnWO4 single crystals and TmhYb3 ion-codoped were grown with Czochralski method after carefully designing temperature field and choosing technique parameters A (1 30 /cm, rotation rate 4mmh and pulling rate 250r.p.m. Annealing in alumina powder which the phase transforms in high temperature increased the transmission in VSR . The result of density experiment showed thulium ions substituted the partial sites of zinc ions to form permutable solid-solution. The distribution coefficient of thulium ion in zinc tungstate, about 0.27, was obtained by ICP-AES method. Absorption spectra of Tm:ZW and Tm,Yb:ZW measured at room temperature exhibited that they were fit to be pumped by 808nm LD due to high to 411cm energy splitting of 3H4 level correspondent to 26.7nm peak width which attributed to the low symmetry, and the energy level distribution of the thulium ion and ytterbium ion in zinc tungstate were confirmed, and the absorption cross section of thulium ion was 1.58 X 1020cm2. In Tm:ZW, pumped by 808nm LD, three upconversion peaks at 404,486 and 695nm can be observed, which attributed to transitions of b3H6,3H6 and 3F3 3H6, respectively. The slope a of the three luminescence intensity versus pump power in double-logarithmic were 1.2,0.8 and 1.2, respectively. But in codoped sample, the intensity of 486nm luminescence increased above two magnitude orders and was the strongest peak, this due to resonance energy transfer from ytterbium ions to thulium ions, a were 2.44,1.81 and 1.13, respectively. The emission cross section of thulium ion was 3.99 X 10cm2.更多还原