Highlights

•

The uniform MoO₃ nanowires have been synthesized via a simple hydrothermal routine.

•

The Pt/MoO₃ obtained by thermal decomposition shows excellent catalytic activity.

•

The better catalysis is due to plenty of active sites and channels at the interface.

Abstract

Single-component white-light phosphors can overcome many of the problems associated with multiple emitting components, such as intrinsic color balance, device complications and high cost. Here, we demonstrate a novel type of single-component white-light Sr_2−xV₂O₇:Eu_x phosphor with dual-luminescence centers (x = 0–0.24) for white light-emitting diodes (LEDs). Due to the charge transfer absorption (${\text{V}}^{5+}{\text{O}}_4^{2-}\to {\text{V}}^{4+}{\text{O}}_4^{2-}$), the white light spectra they emit consist of both a broad photoluminescence band centered at about 518 nm, which would be from VO₄ groups with approximate C_3v symmetry, and a sharp characteristic spectrum (⁵D₀ → ⁷F₂) at about 611 nm from the doped Eu³⁺ ion at the Sr²⁺ sites in the Sr₂V₂O₇ crystal. Moreover, to explain the broad emission spectra of these phosphors, a 10 × 10 energy matrix was successfully established based on an effective operator Hamiltonian, including free ion and crystal field interactions. For the first time, the broad emission spectra for VO₄ groups with the approximate C_3v symmetry were calculated using a complete diagonalization (of energy matrix) method. The fitting and experimental values are close to each other, powerfully demonstrating the nature of this broad emission and the feasibility of using the complete diagonalization method to study the phosphors for white LEDs.

Abstract

Eu³⁺-doped strontium molybdate red phosphors (Sr_1−xMoO₄:Eu_x (x = 0.01–0.2)) for white light-emitting diodes (LED) were synthesized by the solid-state reaction method. The fluorescent intensities of the as-prepared phosphors were remarkably improved. The excitation and emission spectra demonstrate that these phosphors can be effectively excited by the near-UV light (395 nm) and blue light (466 nm). Their emitted red light peaks are located at 613 nm, and the highest quantum yield value (η) of the as-grown red phosphor, which is 95.85%, is much higher than that of commercial red phosphor (77.53%). These red phosphors plus commercial yellow powers (1:10) were successfully packaged with the GaN-based blue chips on a piranha frame by epoxy resins. The encapsulated white LED lamps show high performance of the CIE chromaticity coordinates and color temperatures. Moreover, to explain the fluorescent spectra of these phosphors, a complete 3003 × 3003 energy matrix was successfully built by an effective operator Hamiltonian including free ion and crystal field interactions. For the first time, the fluorescent spectra for Eu³⁺ ion at the tetragonal (S₄) Sr²⁺ site of SrMoO₄ crystal were calculated from a complete diagonalization (of energy matrix) method. The fitting values are close to the experimental results.