A white-light-emitting diode (white LED) with good color rendering index is fabricated based on a blue LED combined with high-fluorescence CdS:Cu/ZnS quantum dots (QDs) and YAG:Ce phosphors. The reabsorption problem is overcome by the excellent optical properties and enlarged Stokes shift of the QDs with low absorption of light of wavelengths longer than 470 nm.

No abstract

No abstract

The layered transition metal dichalcogenide has attracted tremendous attention for its unique structure and electrical and optoelectronic properties. As an emerging two-dimensional material, PdSe2 plays a key role in optoelectronic applications due to its distinct optical and tunable electrical properties. The carrier dynamic and low-frequency phonon modes and how they evolve with the number of layers are important for future device fabrication in photonics, optoelectronics, and nanomechanics. Here, by employing ultrafast optical pump–probe spectroscopy, we have investigated systematically the photocarrier dynamics as well as the thickness dependent interlayer coherent phonon modes in PdSe2 films. Two low-frequency phonon modes in PdSe2 films are identified after photoexcitation at 780 nm. The higher-frequency mode is ascribed to the interlayer breathing mode, and the lower one is assigned to the standing wave mode, and both of the mode frequencies decrease with increasing the number of layers of films. Analysis based on simple one-dimensional chain model produces interlayer force constant K = 5.74 × 1019 N/m3 for the interlayer breathing mode, and sound velocity of v = 8.27 × 104 cm/s for the standing wave mode in PdSe2 film. Our experimental finding paves the way for designing and developing PdSe2-based optoelectronic and nanomechanic devices.

Luminescent Ce 3+ , Eu 3+ co-doped yttrium aluminum garnet (Y 3 Al 5 O 12 , YAG) nanophosphors were successfully synthesized by a facile hydrothermal-assistant combustion method without a reducing atmosphere. The photoluminescence (PL) spectrum of the as-prepared YAG:Ce 3+ , Eu 3+ nanophosphors consisted of a typical broad yellow emission band attributed to the characteristic emission of Ce 3+ and several sharp emission bands in red spectral region attributed to the characteristic emission of Eu 3+ due to the successful co-doping of Eu 3+ into YAG host lattice, and the intensities of these sharp red emission bands could be adjusted by varying the Eu 3+ doping concentration. The energy transfer from Ce 3+ to Eu 3+ inside YAG was also investigated, and the results showed that both Ce 3+ and Eu 3+ could be efficiently excited by 465 nm blue light, which indicated the red emission of YAG:Ce 3+ , Eu 3+ under 465 nm blue light excitation was not merely enhanced at the cost of emission intensity of Ce 3+ . Moreover, YAG: Ce 3+ , Eu 3+ nanophosphors were combined with blue light-emitting diode (LED) chip to fabricate white LED, and the resulting white LED showed good performance with a luminous efficiency of 70.4 lm/W, Ra of 82, and T c of 4964 K at 100 mA.