Yayun Zhou

A new red phosphor BaGeF6:Mn4+: hydrothermal synthesis, photo-luminescence properties, and its application in warm white LED devices

In this work, we report a new and efficient red phosphor BaGeF6:Mn4+ (denoted as BGFM) by hydrothermally etching BaCO3 and GeO2 in HF solution with an optimized KMnO4 concentration. The crystal structure and morphology were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) in detail. The influence of synthesis conditions on its photo-luminescent (PL) properties has been investigated comprehensively. It can present broad adsorption and sharp emissions in blue and red ranges respectively. The white LED device made of a blue GaN chip merged with a YAG:Ce–BGFM mixture presents warmer white light than that merged with only one YAG:Ce component.

A new and efficient red phosphor for solid-state lighting: Cs2TiF6:Mn4+

Cs2TiF6:Mn4+ powder as a novel red phosphor has been successfully fabricated on a large scale through the cation exchange method using K2MnF6 as a Mn4+ source at ambient temperature. The Cs2TiF6:Mn4+ product is well crystallized into a single-phase with a hexagonal micro-rod morphology and presents sharp red emissions under blue light illumination. It can significantly improve Ra and CCT levels of the YAG type white LED used for indoor lighting.

Red-emitting phosphors Na2XF6:Mn4+ (X = Si, Ge, Ti) with high colour-purity for warm white-light-emitting diodes

Red-emitting phosphors Na2XF6:Mn4+ (X = Si, Ge, Ti) were synthesized by a simple co-precipitation method. The crystal structure, morphology and composition of as-prepared phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS) and atomic absorption spectroscopy (AAS). Their optical properties were investigated by photo-luminescent spectra (PL), diffuse reflectance spectra (DRS), and the luminescence decay curves. These phosphors exhibit broad excitation band in blue regions and intense emission in red regions with high color-purity. The sample Na2SiF6:Mn4+ shares bright red emission under blue light excitation, and its CIE coordinates are x = 0.684, y = 0.315, which are close to the NTSC (National Television Standard Committee) standard values for red (x = 0.67, y = 0.33). The white-light-emitting diodes (WLEDs) fabricated with this phosphor emits intense warm white-light with lower color temperature (3930 K) and higher color rendering index (92.3). The above results indicated that red phosphor Na2SiF6:Mn4+ maybe serve as a red-emitting phosphor for application in warm WLEDs.

Highly efficient red phosphor Cs2GeF6:Mn4+ for warm white light-emitting diodes

Red phosphor Cs2GeF6:Mn4+ has been synthesized by the cation exchange method. The as-prepared phosphor was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), atomic absorption spectrophotometer (AAS), thermogravimetry (TG) and differential scanning calorimetry (DSC). Its optical properties were investigated by photo-luminescence spectra (PL), diffuse reflectance spectra (DRS), the low-temperature emission spectrum and the luminescence decay curve. The sample doped with 8.78 mol% Mn4+ exhibits an intense red emission with a high thermal stability and appropriate CIE coordinates (x = 0.69, y = 0.31), and its emission intensity is higher than that of commercial K2TiF6:Mn4+. The white light-emitting diodes (WLEDs) fabricated with this sample exhibit intense warm white-light with a low color temperature (Tc = 3673 K), high color rendering index (Ra = 84.9) and high luminous efficacy (LE = 141.5 lm W−1). So Cs2GeF6:Mn4+ may be a promising red component for warm WLEDs.

Optical performance of Mn4+ in a new hexa-coordinated fluorozirconate complex of Cs2ZrF6

In this work, a Cs2ZrF6:Mn4+ red phosphor, a novel and efficient supplement for commercial Y3Al5O12:Ce3+ type white light-emitting diodes (WLEDs), is successfully fabricated on a large scale through a cation exchange method using K2MnF6 as the Mn4+ source at ambient temperature. The crystal structure and morphology were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), in detail. The complex is well crystallized in a single-phase with particulate morphology and presents sharp red emissions under blue light illumination. From the aspects of Ra and Tc, the optical performance of a WLED made with the Cs2ZrF6:Mn4+ red phosphor supplement is significantly improved and it can be used for indoor lighting applications.

Fabrication and application of non-rare earth red phosphors for warm white-light-emitting diodes

In this work, a facile and efficient method for the preparation of K2XF6:Mn4+ (X = Si, Ti and Ge) red phosphors is reported. They were synthesized by adding KF to precipitate a warm mixed solution with XO2, KMnO4 and HF as raw materials. After the doping of Mn4+, although the obtained products exhibit irregular micro-sized particulate morphologies, they present the same single phases as their matrices and no impurities can be found. The optical properties of the fluoride complexes were investigated using photo-luminescence spectroscopy, diffuse reflectance spectroscopy, and luminescence decay curves. The complexes presented bright red emission under blue light illumination, and warm white-light-emitting diodes with low correlated color temperature, high color rendering index and high luminous efficiency, with values of 3156 K, 84.9 and 138.4 lm W−1, respectively, were achieved by coating a mixture of the red phosphor with commercial Y3Al5O12:Ce3+ on blue-GaN chips.

The Photoluminescent Properties of New Cationic Iridium(III) Complexes Using Different Anions and Their Applications in White Light-Emitting Diodes

Three cationic iridium(III) complexes [Ir(ppy)2(phen)][PF6] (C1), [Ir(ppy)2(phen)]2SiF6 (C2) and [Ir(ppy)2(phen)]2TiF6 (C3) (ppy: 2-phenylpyridine, phen: 1, 10-phenanthroline) using different anions were synthesized and characterized by 1H Nuclear magnetic resonance (1HNMR), mass spectra (MS), Fourier transform infrared (FTIR) spectra and element analysis (EA). After the ultraviolet visible (UV-vis) absorption spectra, photoluminescent (PL) properties and thermal properties of the complexes were investigated, complex C1 and C3 with good optical properties and high thermal stability were used in white light-emitting diodes (WLEDs) as luminescence conversion materials by incorporation with 460 nm-emitting blue GaN chips. The integrative performances of the WLEDs fabricated with complex C1 and C3 are better than those fabricated with the widely used yellow phosphor Y3Al5O12:Ce3+ (YAG). The color rendering indexes of the WLEDs with C1 and C3 are 82.0 and 82.6, the color temperatures of them are 5912 K and 3717 K, and the maximum power efficiencies of them are 10.61 Lm·W−1 and 11.41 Lm·W−1, respectively.

Luminescent properties and energy transfer in the green phosphors LaBSiO5:Tb3+, Ce3+.

LaBSiO5 phosphors doped with Ce(3+) and Tb(3+) were synthesized using the conventional solid-state method at 1100 °C. The phase purity and luminescent properties of these phosphors are investigated. LaBSiO5:Tb(3+) phosphors show intense green emission, and LaBSiO5 phosphors doped with Ce(3+) show blue-violet emission under UV light excitation. LaBSiO5 phosphors co-doped with Ce(3+) and Tb(3+) exhibit blue-violet and green emission under excitation by UV light. The blue-violet emission is due to the 5d-4f transition of Ce(3+) and the green emission is ascribed to the (5) D4 → (7) F5 transition of Tb(3+). The spectral overlap between the excitation band of Tb(3+) and the emission band of Ce(3+) supports the occurrence of energy transfer from Ce(3+) to Tb(3+), and the energy transfer process was investigated.