Optical energy storage-type tunable long-lasting phosphorescence of low valent rare-earth ions using crystal-field distributions

在具有晶场分布的晶体中，低价稀土离子(Eu^&lt；2+&gt；，Ce^&lt；3+&gt；，Sm^&lt；2+&gt；)有望在可见光区产生持久的磷光，并显示出新的光学现象。我们制备了具有无序结构的新型黄长石型铝硅酸盐、具有超结构的硅酸钡和氟化物。我们研究了非相干紫外光或近红外飞秒激光激发产生的长余辉发光和光反应的光学性质、局域结构和机理。本研究的研究结果总结如下：1.紫外光激发新的掺Eu^&lt；2+&gt；黄长石Me_2a_3O_7(Me=Ca，Sr，Y，Gd；B=Al，Si)产生蓝色和苦橙区Eu&lt；2+&gt；离子的长余辉发光。温度依赖关系是由包括辐射和非辐射过程的衰减率得出的。我们提出了黄长石晶体中Eu~(2+)&Gt~(2+)的磷光模型：(1)电子和空穴对…更多的电子或空穴在Eu^&lt；2+&gt；离子的紫外光激发下产生，移动到稳定的俘获中心。(2)电子或空穴通过热跳跃和隧穿重新回到Eu^&lt；2+&gt；，并辐射复合。新发现的掺Eu、Lt；2+、Gt；的硅酸盐(Ba2SiO4、BaSi2O5、Ba3SiO5)在蓝色和苦橙区有长余辉发光。这种衰变是由于电子-空穴对通过隧道复合造成的。生长了三价Eu、Lt；3+、Gt；掺杂的Ca2Al2SiO7黄长石单晶。在红外区观察到了飞秒激光诱导的明亮而持久的磷光。这是首次用红外激光激发观察到三价Eu~(3+)~(3+)在红区的长余辉发光。掺Ce&lt；3+&Gt；的黄长石晶体Ca2Al2SiO7和CaYAl3O7的紫外光激发除了产生本征发光外，还产生了长余辉发光。磷光可以用捕获的电子和空穴的远方对复合的模型来解释。紫外光激发产生的自陷空穴Al^&lt；4+&gt；通过隧穿和热跳跃返回到Ce^&lt；3+&gt；位，而Ce^&lt；4+&gt；的俘获空穴通过隧穿以F~+中心的形式辐射复合。它与用激活能在由势垒隔开的孔洞之间跳跃有很强的关联。生长了新型荧光粉Ce^&lt；3+&gt；和Sm^&lt；3+&gt；Sm^&lt；2+&gt；和Ce^&lt；3+&gt；掺杂CaNaYF6。掺Ce~(3+)&Gt~(3+)的BaMgF_4晶体具有与之相称的抑制基团。在飞秒激光作用下，BaMgF_4中的部分Sm^&lt；3+&gt；被转化为Sm^&lt；2+&gt；BaMgF_4：Sm^&lt；3+&gt；/Sm^&lt；2+&gt；晶体具有潜在的应用前景。分析了CaAF6晶体中的无序对Ce^&lt；3+&gt；发光非均匀展宽的影响。掺Ce^&lt；3+&Gt；的CaNaYF6晶体有望成为一种从近紫外区到绿色区具有更宽可调谐性的激光新材料。较少

Low valent rare-earth ions(Eu^<2+>,Ce^<3+>,Sm^<2+>) in crystals with crystal-field distributions are expected to produce long-lasting phosphorescence in visible region and to show novel optical phenomena. We have prepared new melilite-type aluminosilactes with disordered stuructures, Ba silicates, and fluondes with superstructures. We have examined the optical properties, the local structures, and the mechanism of long-lasting phosphorescence and photoreaction produced by the incoherent UV light or near IR femtosecond laser excitaion. The results of this study are summarized as follows.1. UVexcitation for new Eu^<2+>-doped melilite Me_2A_3O_7(Me=Ca,Sr,Y,Gd;B=Al,Si) produces long-lasting phpsphorescence from Eu<2+> ions in the blue and bitter orange regions. The temperature dependence is derived from decay rates including both radiative and non-radiative processes. We proposed the following model of the phosphorescence of Eu^<2+> in the melilite crystals.(1) Pairs of electrons and holes … More are produced at Eu^<2+> ions by the UV excitation, move to stable trapped centers.(2) The electrons or holes again back to Eu^<2+> through thermal hopping ana tunneling, and recombine radiatively.2. Long-lasting phosphorescence in the blue and bitter orange regions has been observed for newly discoverd Eu^<2+>-doped Ba-silicates(Ba_2SiO_4, BaSi_2O_5,Ba_3SiO_5). The decay is due to the recombination of the electron-hole pairs through tunneling.3. Trivalent Eu^<3+> -doped Ca_2Al_2SiO_7 melilite single crystals were grown. Infrared femto-second laser-induced bright and long-lasting phosphorescence in the red region was observed. This is first obsevation of long-lasting phosphorescence of trivalent Eu^<3+> in the red region by the infrared laser excitation.4. UV excitation of Ce^<3+>-doped melilite crystals Ca_2Al_2SiO_7 and CaYAl_3O_7 produces long-lasting phosphorescence besides intrinsic Ce^<3+> luminescence. The phosphorescence is explained by a model of the recombination of distant paires of trapped electrons and holes. The self -trapped holes, Al^<4+>, produced by the UV excitation move back to Ce^<3+> sites throug tunneling and thermal hopping, and the trapped holes of Ce^<4+> recombine radiatively the trapped electrons in the form of F^+ centers through tunnling. It is strongly related to hopping between the adiacent self-trapped staes of holes speparated by a barrier with the activetion energy.5. New phosphors, Ce^<3+> -and Sm^<3+>Sm^<2+>-doped BaMgF_4 and Ce^<3+>-doped CaNaYF6 were grown. Ce^<3+>-doped BaMgF_4 crystal exmoits a commensurate supser siruciurre. After the irradiation by the femtosecond laser, a part of Sm^<3+> in BaMgF_4 was converted to Sm^<2+>. The BaMgF_4:Sm^<3+>/Sm^<2+> crystal nas a potential for applications in opucai siorage. the effects of disorder in the CaNaF_6 crystal on the inhomogeneous brodening of the Ce^<3+> luminescence was analyzed. The Ce^<3+>-doped CaNaYF_6 crystal has a potential as a new material capable of lasing with wider tunability from the near UV to green regions. Less