Leifeng Chen

Garnet-based Li6CaLa2Sb2O12:Eu3+ red phosphors: a potential color-converting material for warm white light-emitting diodes

To alleviate the issues of low thermal stability and high correlated color temperature, exploring an inorganic color converter with both yellow- and red-emissions to replace the conventional resin/silicone-based phosphor converter for obtaining high-power warm white light-emitting diodes is highly desired. In this study, a series of garnet-based Li6CaLa2−2xEu2xSb2O12 (x = 0.1–1.0) red phosphors have been successfully synthesized by a conventional high-temperature solid-state method. The microstructure and luminescence properties were systematically investigated by X-ray diffraction, emission/excitation spectra, luminescence lifetimes and temperature-dependent decays. The as-synthesized phosphors exhibited a highly efficient red luminescence at 611 nm corresponding to the 5D0–7F2 electric dipole transition of Eu3+, and the luminescence monotonously enhanced as the Eu3+ content was increased to 100 mol%. The absence of concentration quenching was ascribed to the large Eu3+–Eu3+ distance (7.048–7.105 A) and subsequently the hindering of unwanted energy migration among them in the Li6CaLa2Sb2O12 crystalline lattice. Impressively, the Li6CaLaEuSb2O12 phosphor showed an excellent thermal stability with only 9.7% emission loss when the recording temperature was increased from 293 K to 553 K. To evaluate the suitability of Li6CaLa2Sb2O12:Eu3+ as a red converter, both the garnet-based Y3Al5O12:Ce3+ yellow and Li6CaLa2Sb2O12:Eu3+ red phosphor co-doped glass ceramics were successfully fabricated by a low-temperature co-sintering technique. Importantly, the adverse energy transfers between Ce3+ and Eu3+ were efficiently suppressed due to the spatial separation of Ce3+ in Y3Al5O12 and Eu3+ in Li6CaLa2Sb2O12 in the crystal lattice. As a consequence, the quantum yield of the glass ceramic reached as high as 89.3%, and the constructed white light-emitting diode exhibited an optimal luminous efficacy of 101 lm W−1, a correlated color temperature of 5449 K and a color rendering index of 73.7. It is expected that the developed Li6CaLa2−2xEu2xSb2O12 red phosphors and the related glass ceramics should have potential applications in high-power warm white light-emitting diodes.

Field emission performance enhancement of Au nanoparticles doped graphene emitters

Graphene (GP) field emitters fabricated by the electrophoretic deposition (EPD) and their field emission performance can be enhanced and tailed simultaneously by chemical doping Au nanoparticles (NPs). It was found that doped Au NPs could both decrease the resistance of GP emitters and increase the density of field emission sites. The Au-doped GP emitters showed lower turn-on voltage, lower threshold field, higher field enhancement factor, higher luminance intensity, and emitting uniformity, compared with that of pristine GP. This study will provide us to further understand the role of doping effect on the GP emitters used for the future display.

Effectively Improved Field Emission Properties of Multiwalled Carbon Nanotubes/Graphenes Composite Field Emitter by Covering on the Si Pyramidal Structure

The composite nanostructure emitter of multiwalled carbon nanotubes and graphenes was deposited on pyramidal silicon substrate by the simple larger scale electrophoretic deposition process. The field emission (FE) properties of the composite/pyramidal Si device were greatly improved compared with that of the composite/plain Si. The low turn-ON electric field, the low threshold electric field, and the larger enhancement factor were obtained using the pyramidal structure. The better FE performances of the composite/pyramidal Si were a combined effect of the field enhancement from the composite emitter and the pyramidal Si structure. The numerical simulation of the electric field distribution on composite/pyramidal cathode was used to illuminate the improved FE properties by using the pyramidal substrate. These studies indicate that constructing composite/pyramidal structure is one of the efficient ways to improve the FE properties.