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A 365-nm UV LED was fabricated based on embedded nanoporous AlGaN distributed Bragg reflectors (DBR) by electrochemical etching. The porous DBR had a reflectance of 93.5% at the central wavelength of 365 nm; this is the highest value of porous AlGaN DBRs below 370 nm which has been reported so far. An innovative two-step etching method with a SiO2 sidewall protection layer (SPL) was proposed to protect the n-AlGaN layer and active region of UV LED from being etched by the electrolyte. The DBR-LED with SPL showed 54.3% improvement of maximal external quantum efficiency (EQE) and 65.7% enhancement of optical power at 100 mA without any degeneration in electrical properties, compared with the un-etched standard LED sample. This work has paved the way for the application of electrically-pumped UV LEDs and VCSELs based on nanoporous AlGaN DBRs.

The polycrystalline Eu 2+ and Dy 3+ codoped strontium aluminates SrAl 2 O 4 : Eu 2+ ,Dy 3+ were prepared by a solid-state reaction. The UV-excited photoluminescence, persistent luminescence, and thermoluminescence of the SrAl 2 O 4 : Eu 2+ ,Dy 3+ phosphors with different compositions and ion doping was studied and compared. The results showed that the Eu 2+ ion doped in SrAl 2 O 4 : Eu 2+ ,Dy 3+ phosphors is not only the UVexcited luminescent center but also the persistent luminescent center. The Dy 3+ ion introduced into SrAl 2 O 4 : Eu 2+ crystal matrix can hardly yield any luminescence under UV excitation but acts as an electron trap with a suitable depth for persistent luminescence. The Dy 3+ codoping would effectively enhance the persistent luminescence and thermoluminescence. Different codoping RE 3+ ions have a different effect on persistent luminescence. Only the RE 3+ ions (for example, Dy 3+ and Nd 3+ ), which have suitable optical electronegativity, can form suitable electron traps and effectively improve the persistent luminescence of SrAl 2 O 4 : Eu 2+ . Based on the above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated.