量子点单光子源的光纤耦合

半导体量子点在低温下产生谱线细锐的激子发光可制备单光子源.光纤耦合可避免低温共聚焦装置扫描定位和振动影响,是实现单光子源即插即用和组件化的关键技术.在耦合工艺上,基于微区定位标记发展出拉锥光纤与光子晶体腔或波导侧向耦合、大数值孔径锥形端面光纤与量子点样片垂直耦合等技术;然而,上述工艺需要多维度精密调节以避免柔软光纤的畸形弯曲实现对准和高效耦合.陶瓷插针或石英V槽封装的光纤无弯曲且具有大平滑端面,只要与单量子点样片对准贴合就可保证垂直收光, V槽封装的排式光纤还可通过盲对粘合避免扫描对准,耦合简单.本文在前期排式光纤粘合少对数分布Bragg反射镜(distributed Bragg reflector, DBR)微柱样片实现单光子输出基础上,经理论模拟采用多对数DBR腔提升样片垂直出光和光纤收光效率,使光纤输出单光子计数率大大提升.     

Local Structure Mediation and Photoluminescence of Ce~(3+)-and Eu~(3+)-Codoped YAG Nanophosphors

Cerium and europium codoped yttrium aluminum garnet(YAG:Ce,Eu) nanophosphors were prepared by sol-gel method.We systematically explored the structure,composition,morphology and photoluminescence(PL) properties by using X-ray diffraction,scanning electron microscope,high resolution transmission electron microscope,energy dispersive spectrometer,photoluminescence emission and excitation spectra techniques,and focused on clarifying the change of local structure surrounding Ce~(3+) ions by utilizing advanced quantitative ~(27)Al magic angle spinning nuclear magnetic resonance spectroscopy.The results show that the lattice constant slightly increases as the Ce~(3+) and Eu~(3+) ions incorporate,and the geometric distortion of local structure surrounding Ce~(3+) activator introduced by the incorporated Eu~(3+) coactivator causes the variation of crystal field,which results in red shift of Ce~(3+) PL emitting in YAG:Ce,Eu nanophosphor.Furthermore,the YAG:Ce,Eu nanophosphors could exhibit several sharp and narrow ~5D_0 → ~7F_J(J = 1~4) emissions of Eu~(3+) ion besides the classic broad ~5d_1 → ~4f(~2F_(5/2),~2F_(7/2)) emissions of Ce~(3+) ion under near ultraviolet(UV) excitation.