Float zone growth of rare-earth doped lutetium orthovanadate single crystals as new solid state laser materials

钕掺杂正钒酸镥（Nd: LuVO_4）具有比常规掺钕稀土正钒酸镥更大的吸收和发射截面，有望应用于激光二极管泵浦固体激光器。由于Lu^<3+>的tonic半径与Tm^<3+>和Yb^<3+>的tonic半径相当，因此LuVO_4也有望成为Tm和Yb的良好宿主晶体。本文建立了利用浮区技术生长稀土（Nd， Tm和Yb）掺杂LuVO_4单晶的方法，并对其作为激光材料的一些光谱特性进行了研究。每种掺杂剂的添加量为0.5-4，相对于Lu %。生长条件为：熔融区移动速度为20 ~ 40 mm/h；转速30 ~ 40 RPM；方向为[110]，气氛为氧流。任何生长的晶体呈黄褐色，但在空气中1000℃退火20h后，颜色完全消除。偏光显微镜观察表明，生长的晶体不含宏观缺陷，只有掺钕的晶体中存在生长条纹。测定了Tm和Yb的有效偏析效率接近统一，Nd的有效偏析效率约为0.5。在这个阶段，在tm和yb掺杂高达5% At %和nd掺杂高达1% At %的情况下，可以再生地生长出直径5mm，长50mm的单晶。Nd: LuVO_4的吸收系数是其他稀土正钒酸盐的1.4倍。Nd: LuVO_4 （1 at%）单晶在880 nm泵浦下表现出优异的激光性能；即斜率效率为73%，阈值为7mw。虽然Tm和yb掺杂晶体的激光振荡实验还在进行中，但基于其优异的光谱特性，可以期待这些晶体也能表现出良好的激光性能。

Neodymium-doped lutetium orthovanadate (Nd : LuVO_4) has larger absorption and emission cross sections as compared with conventional Nd-doped rare earth orthovanadates and is expected to be applied for laser-diode pumped solid state lasers. LuVO_4 is also expected to be a good host crystal for Tm and Yb, since the tonic radius of Lu^<3+> is comparable to those of Tm^<3+> and Yb^<3+>. In this study, the growth technique of rare-earth (Nd, Tm and Yb) doped LuVO_4 single crystals by the floating zone technique has been established and some spectroscopic properties as a laser material have been investigated.Each dopant was added with 0.5-4 at% with respect to Lu. Growth conditions were as follows : traveling rate of the molten zone was 20-40 mm/h ; rotation rate was 30-40 rpm ; direction was [110] and atmosphere was an oxygen flow Any as-grown crystal was colored in yellowish ocher, but the coloring was completely eliminated by annealing at 1000 ℃ for 20h in air. Polarizing microscopy proved that the grown crystals contained no macroscopic defects but growth striations were observed only in Nd-doped crystals. Effective segregation efficient was determined to be close to unity for Tm and Yb and about 0.5 for Nd. At this stage, single crystals 5 mm in diameter and 50 mm long have been grown reproducibly for Tm-and Yb-doping of up to 5 at% and Nd-doping of up to 1 at%.The absorption coefficient of Nd : LuVO_4 was 1.4 times as high as those of other rare-earth orthovanadates. The Nd : LuVO_4 (1 at%) single crystal exhibited excellent laser performance with 880 nm pumping ; that is, the slope efficiency was 73 % and the threshold was 7 mW. Although the laser oscillation experiments for Tm and Yb-doped crystals are underway, it is expected that those crystals also exhibit good laser performance on the basis of their excellent spectroscopic properties.