RESUMEN
Long-wavelength broadband near-infrared (NIR) phosphors have attracted considerable interest in the fields of medical cosmetology and organic detection because of their special emission band. Herein, Ca2GeO4(CGO): Cr4+ NIR phosphor, presenting a broadband emission with longer wavelength ranging from 1100 to 1600 nm, has been synthesized. Further, the luminescence intensity and quantum efficiency of Cr4+ could be obviously improved via the energy transfer from Eu3+ to Cr4+. The energy transfer is dominated by the dipole-dipole mechanism, which can be inferred from the spectra and the decay curves. Furthermore, in order to evaluate the potential application, an NIR phosphor-converted light-emitting diode (pc-LED) based on blue chip has been prepared. Consequently, CGO: Eu3+, Cr4+ exhibits proper output power and wider half-width than the NIR LED chip, indicating its great prospect for long-wavelength NIR pc-LED applications.
RESUMEN
Developing broadband cyan-emitting phosphors is an essential issue to achieve high-quality full-spectrum phosphor-converted white light-emitting diodes. Multisite cation regulation to modify the photoluminescence spectrum is a valid way to achieve broadband emission for phosphors. The Ba9Lu2Si6O24 lattice with various cation sites for activator ions is a preferred host for broadband emitting phosphors. The preferential crystallographic sites of Eu2+ in the Ba9Lu2Si6O24 lattice are identified based on the crystal field theory, crystal structure, and bond indices (such as NAC and SBOs) of the cations. Sr substitution in Ba9Lu2Si6O24/Eu2+ phosphor affects the location of Eu2+ activator ions, which is investigated via the first-principles density functional theory calculations, Rietveld refinement, and luminescence decay curves, and results in the modification of luminescence properties and thermal stability. The Sr-substituted (Ba0.8Sr0.2)9Lu2Si6O24/Eu2+ sample exhibits a broadband emission spectrum peaked at 471 and 518 nm with a large full width half maximum of 139 nm, covering blue-cyan-green regions, which can be an excellent candidate as broadband cyan-emitting phosphors for high-quality full-spectrum wLEDs.
RESUMEN
High-quality white light-emitting diodes (w-LEDs) are mainly determined by conversion phosphors and the enhancement of cyan component that dominates the high color rendering index. New phosphors (Lu2M)(Al4Si)O12:Ce3+ (M = Mg, Ca, Sr and Ba), showing a cyan-green emission, have been achieved via the co-substitution of Lu3+-Al3+ by M2+-Si4+ pair in Lu3Al5O12:Ce3+ to compensate for the lack of cyan region and avoid using multiple phosphors. The excitation bands of (Lu2M)(Al4Si)O12:Ce3+ (M = Mg, Ca, Sr and Ba) show a red-shift from 434 to 445 nm which is attributed to the larger centroid shift and crystal field splitting. The enhanced structural rigidity associated with the accommodation of larger M2+ leads to a decreasing Stokes shift and the corresponding blue-shift (533 â 511 nm) in emission spectra, along with an improvement in thermal stability (keeping â¼93% at 150 °C). The cyan-green phosphor Lu2BaAl4SiO12:Ce3+ enables to fabricate a superhigh color rendering w-LED ( Ra = 96.6), verifying its superiority and application prospect in high-quality solid-state lightings.
RESUMEN
On the basis of a rough rule of thumb that the difference in ionic radius for the interstitial cationic pair may affect the structure of some nitride and carbonitride compounds, a novel carbonitride phosphor, YScSi4N6C:Ce3+, was successfully designed. The crystal structure (space group P63mc (No. 186), a = b = 5.9109(8) Å, c = 9.67701(9) Å, α = ß = 90°, γ = 120°) was characterized by single-crystal synchrotron X-ray diffraction and further confirmed by powder X-ray diffraction and refined with Rietveld methods. Ce3+-doped YScSi4N6C shows a broad excitation band ranging from 280 to 425 nm and a broad cyan emission band peaking at about 469 nm upon excitation by near-UV light (400 nm). The mechanism of thermal quenching for this phosphor was also investigated. In addition, a white light-emitting diode (w-LED) was prepared by coating a near-UV chip (λem = 405 nm) with YScSi4N6C:Ce3+, ß-sialon:Eu2+ (green), and CaAlSiN3:Eu2+ (red) phosphors. It emitted a well-distributed warm white light with high color rendering index (CRI) of 94.7 and a correlated color temperature (CCT) of 4159 K. The special color rendering index R12 of the obtained white light was as high as 88. All of the results indicate that this novel phosphor can compensate for the cyan cavity and has potential applications in the full-spectrum lighting field.
