Valence state manipulation of Sm3＋ ions via a phase-shaped femtosecond laser field

The ability to manipulate the valence state conversion of rare-earth ions is crudal for their applications in color displays, optoelectronic devices, laser sources, and optical memory. The conventional femtosecond laser pulse has been shown to be a well-established tool for realizing the valence state conversion of rare-earth ions, although the valence state conversion efficiency is relatively low. Here, we first propose a femtosecond laser pulse shaping tech- nique for improving the valence state conversion effidency of rare-earth ions. Our experimental results demonstrate that the photoreduction emciency from Sm3＋ to Sm2＋ in Sm3＋-doped sodium aluminoborate glass using a zt phase step modulation can be comparable to that using a transform-limited femtosecond laser field, while the peak laser intensity is decreased by about 63%, which is very beneficial for improving the valence state conversion efficiency under the laser-induced damage threshold of the glass sample. Furthermore, we also theoretically develop a （2 ＋ 1） resonance-mediated three-photon absorption model to explain the modulation of the photoreduction efficiency from Sm3＋ to Sm2＋ under the π-shaped femtosecond laser field.

Enhanced optical and thermal performance of white light-emitting diodes with horizontally layered quantum dots phosphor nanocomposites

Due to their good color rendering ability, white light-emitting diodes(WLEDs) with conventional phosphor and quantum dots(QDs) are gaining increasing attention. However, their optical and thermal performances are still limited especially for the ones with QDs-phosphor mixed nanocomposites. In this work, we propose a novel packaging scheme with horizontally layered QDs-phosphor nanocomposites to obtain an enhanced optical and thermal performance for WLEDs. Three different WLEDs, including QDs-phosphor mixed type, QDsoutside type, and QDs-inside type, were fabricated and compared. With 30 wt. % phosphor and 0.15 wt. % QDs nanocomposite, the QDs-outside type WLED shows a 21.8% increase of luminous efficiency, better color rendering ability, and a 27.0% decrease of the maximum nanocomposite temperature at 400 mA, compared with the mixed-type WLED. The reduced re-absorption between phosphor and QDs is responsible for the performance enhancement when they are separated. However, such reduced absorption can be traded off by the improper layered configuration, which is demonstrated by the worst performance of the QDs-inside type. Further, we demonstrate that the higher energy transfer efficiency between excitation light and nanocomposite in the QDs-outside type WLED is the key reason for its enhanced optical and thermal performance.