Strong Green Emission from α-SiAlON Activated by Divalent Ytterbium under Blue Light Irradiation

Photoluminescence and Thermoluminescence in Dy3+ , Ce3+ and Tb3+ activated MgB4 O7 phosphor for dosimetry application

Samples of microcrystalline rare earth doped magnesium borate materials were synthesized via. modified solid state diffusion and were characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) techniques. Photoluminescence (PL) results of MgB₄ O₇ :Dy sample depicts blue emission resulted from (⁴ F_9/2 -⁶ H_15/2 ) transition peaked at 484 nm, which is much stronger than yellow emission arising due to the (⁴ F_9/2 -⁶ H_13/2 ) at 576 nm. From emission spectra of MgB₄ O₇ :Tb, it looks that, at higher concentration of Tb³⁺ ion, the green emission becomes strong and strong which directly relates the energy transfer from ⁵ D₃ excited state to ⁵ D₄ excited state by a cross-relaxation while blue emission gets suppressed in MgB₄ O₇ phosphors. The TL of the samples was taken immediately after the irradiation and compared the TL curve with CaSO₄ :Dy. MgB₄ O₇ :Dy showed very good TL sensitivity for the desirable dosimetric curve at about 218°C and the best glow curve structure. In comparison to dosimetric peak of MgB₄ O₇ :Ce and MgB₄ O₇ :Tb, MgB₄ O₇ :Dy phosphor is equally sensitive to CaSO₄ : Dy. MgB₄ O₇ :Dy and MgB₄ O₇ :Tb have shown linearity for 1-5 kGy dose. The activation energies and frequency factors are also calculated for samples MgB₄ O₇ :RE (RE=Dy, Tb, Ce) using peak shape method.

A broadband yellow Yb2+-doped oxynitride phosphor for high-performance white light-emitting diodes

A broadband, efficient and stable yellow (Ba,Sr)Si3Al3O4N5:Yb2+ phosphor shows promising applications in single-phosphor-converted warm w-LEDs.

Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives

Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general illumination, backlighting, and laser-driven lighting. Finally, the challenges and outlooks in this type of promising down-conversion materials are highlighted.

Ca-α-SiAlON:Eu Phosphors: Oxidation States, Energy Transfer, and Emission Enhancement by Incorporation-Aimed Surface Engineering

Ca-α-SiAlON:Eu is one of the most promising phosphors exhibiting potential applications in high power LEDs owing to its excellent thermal stability and relatively high luminescence efficiency comparable to YAG:Ce commercial phosphors. The oxidation states of Eu ions in Ca-α-SiAlON:Eu are still questionable, and furthermore it exhibits lower luminescence intensity than commercial yellow phosphors. Therefore, in the present work, the valences of Eu ions in Ca-α-SiAlON have been examined, from which a mixture of divalence and trivalence is observed. Further improvement in emission intensity involves finding a way to increase the incorporation of larger Eu ions into the Ca-α-SiAlON. Here, we observed preferred doping of Eu around phosphor grain surface and then propose a surface engineering strategy involving HF pickling of glassy surface layer, formation of Eu-rich precursors, and finally post-annealing, aiming to increase surface incorporation of Eu ions. The surface engineered samples exhibit great enhancement in emission intensity with a maximum increment by 80%.

Co-doping effect of Mn2+ on fluorescence thermostability of Ca-α-sialon:Eu2+ phosphors

To reveal Mn²⁺ influence on emission of Ca-α-sialon:Eu²⁺, the Mn²⁺ and Eu²⁺ co-doped phosphors were synthesized by a solid state reaction method. The produced powders show an enhanced fluorescence thermostability and the roles of Mn²⁺ addition have been investigated.

Multiple doping structures of the rare-earth atoms in β-SiAlON:Ce phosphors and their effects on luminescence properties

The critical doping structures of rare-earth atoms in the promising β-SiAlON phosphors have long been argued owing to the lack of direct evidence. Here, the exact locations and coordination of the Ce rare-earth atoms in the β-SiAlON structure have been examined using an atom-resolved Cs-corrected scanning transmission electron microscope. Three different occupation sites for the Ce atoms have been directly observed: two of them are in the structural channel coordinated with six and nine N(O) atoms, respectively; the other one is the unexpected substitution site for Si(Al). The chemical valences and stabilities of the doping Ce ions at the different occupation sites have been evaluated using density functional calculations. Correlation of the different doping structures with the luminescence properties has been investigated by the aid of cathodoluminescence (CL) microanalysis, which verifies the different contribution of the interstitial trivalent Ce ions to the light emission while no luminescence is observed for the substitutional doping of quadrivalent Ce.

Double substitution induced tunable photoluminescence in the Sr2Si5N8:Eu phosphor lattice

The incorporation of La³⁺–Al³⁺ ion pairs into Sr_1.95Eu_0.05Si₅N₈ leads to an additional emission band with maximum at about 760 nm.

White emission of Yb²⁺:fluoride glasses efficiently excited with near-UV light

Various Yb²⁺-containing fluoride glasses melting under a reductive atmosphere were prepared. The brightest white light emission was observed for an AlF₃-based fluoride glass not containing Hf or Zr. The largest full width at half maximum of the white emission spectra was 202 nm. In addition, incorporation of chloride into the AlF₃-based glass enabled efficient excitation with near-ultraviolet light corresponding to a GaN bandgap of 3.4 eV and the maximum internal quantum efficiency of Yb²⁺: AlF₃-based fluoride glass was 42%.

Synthesis and Photoluminescence Properties of Two-Bands Excited SrSi2O2N2: Yb2+ Phosphors

The crystal structure and luminescent properties of synthesized SrSi2O2N2: Yb2+ phosphors have been investigated to seek for convention phosphor for white light-emitting diode applications. The Sr1-xYbxSi2O2N2 phosphors have yellow-red luminescence under the exciting of blue light, which is attributed to the 4fn↔4fn-15d transitions of Yb2+. Although the chemical compositions for Sr1-xYbxSi2O2N2 materials are different, no shifts are observed from the excitation and emission spectra.

Photoluminescence properties of β-SiAlON:Yb2+, a novel green-emitting phosphor for white light-emitting diodes

We have synthesized Yb²⁺-activated Si_6-z Al _z O _z N_8-z (0.05⩽z⩽2.3, 0.03 mol% ⩽Yb²⁺⩽0.7 mol%) green phosphors by solid-state reaction at 1900 °C for 2 h under a nitrogen pressure of 1.0 MPa. Phase purity, photoluminescence and its thermal quenching were investigated. A single phase was obtained for all values of z and Yb²⁺ concentration. A distinct emission band was observed at 540 nm originating from the 5d-4f electronic transition in Yb²⁺ under 480 nm excitation. The photoluminescence properties mainly depended on the Yb²⁺ concentration and chemical composition of the matrix. The resultant phosphor showed high thermal stability, that is, the emission intensity at 150 °C was about 82% of that measured at room temperature. The experimental results indicate that β-SiAlON:Yb²⁺ is a potential green phosphor for white light-emitting diodes (LEDs), which use blue LEDs as the primary light source.

Low-energy cathodoluminescence microscopy for the characterization of nanostructures

Spatially and spectrally resolved low-energy cathodoluminescence (CL) microscopy was applied to the characterization of nanostructures. CL has the advantage of revealing not only the presence of luminescence centers but also their spatial distribution. The use of electrons as an excitation source allows a direct comparison with other electron-beam techniques. Thus, CL is a powerful method to correlate luminescence with the sample structure and to clarify the origin of the luminescence. However, caution is needed in the quantitative analysis of CL measurements. In this review, the advantages of cathodoluminescence for qualitative analysis and disadvantages for quantitative analysis are presented on the example of nanostructures.

Rare-Earth Activated Nitride Phosphors: Synthesis, Luminescence and Applications

Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, etc. Recently, the luminescence of rare earth doped nitridosilicates has been extensively studied, and a novel family of luminescent materials has been developed. This paper reviews the synthesis, luminescence and applications of nitridosilicate phosphors, with emphasis on rare earth nitrides in the system of M-Si-Al-O-N (M = Li, Ca, Sr, Ba, La) and their applications in white LEDs. These phosphors exhibit interesting luminescent properties, such as red-shifted excitation and emission, small Stokes shift, small thermal quenching, and high conversion efficiency, enabling them to use as down-conversion luminescent materials in white LEDs with tunable color temperature and high color rendering index.

Combustion synthesis of novel Li 0.9 Y(0.9-x-y)Zr 0.1 O2:Eu x 3+, R y 3+(R = Ce,Bi) red luminescence nanocrystal and emission-mechanism research

Novel Li(0.9)Y((0.9-x-y))Zr(0.1)O(2):Eu(x)(3+), R(y)(3+) (R = Ce,Bi) red nanocrystal phosphors were synthesized by the sol-combustion process at 800 degrees C. XRD and TEM were used to evaluate the crystallinity and the morphological characterization of the samples. The photoluminescence properties and lifetime of the obtained phosphor nanoparticles were measured using an Edinburgh FLS920 at room temperature. The result showed that the luminescence intensity of Li(0.9)Y((0.9-x-y))Zr(0.1)O(2):Eu(x)(3+) was increased by Bi(3+) and Ce(3+) by 900% and 600%, respectively. The emission mechanism and sensitization mechanism of Bi(3+) and Ce(3+) on Eu(3+) emission intensity were described and explained in detail in this work. The high bright and color-uniform fluorescence images of the doped samples with short luminescence decay times (nanosecond level) confirmed the potential applications of the phosphors in light-emitting diodes and display devices.