Cerium-doped Yttrium Aluminum Garnet Research Articles

YAG:Ce 3+ nanostructured particles obtained via spray pyrolysis of polymeric precursor solution

Cerium-doped yttrium aluminum garnet (YAG:Ce 3+) powder phosphor is synthesized via spray pyrolysis of polymeric precursor solution obtained by dissolving the corresponding nitrates in ethylenediaminetetraacetic acid (EDTA). Ultrasonically generated aerosol droplets are decomposed at 600 °C in argon atmosphere. Following the initial attempt in providing pure YAG:Ce 3+ phase generation the particles were additionally thermally treated for 3 h in air at 1000 and 1100 °C. The powder morphology is followed with scanning electron microscopy (SEM), while inner particle structure is analysed by analytical and high-resolution transmission electron microscopy (TEM). Phase identification is performed by X-ray powder diffraction (XRPD) based on which a structural refinement through Rietveld method was done. The spherical submicronic particles have grained sub-structure comprising clustered garnet monocrystals sized below 100 nm. The YAG:Ce 3+ emission shows wide peak in the range 470–600 nm with the maximum near 520 nm.

Sol–gel preparation and photoluminescence properties of Ce 3+-activated Y 3Al 5O 12 nano-sized powders

Trivalent cerium-doped yttrium aluminum garnet (YAG:Ce 3+) nanoparticles were successfully prepared by a facile sol–gel technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were used to characterize the as-prepared phosphors. Well-crystallized fine nanoparticles were obtained at 1000 °C. Single-crystal nanoparticles with irregular shapes were obtained, with crystallite sizes ranging between 20 and 60 nm. PL intensity of the particles increased monotonically with decreasing Ce doping concentration and showed the maximum value at 0.1 at%.

Synthesis and Electron−Phonon Interactions of Ce3+-Doped YAG Nanoparticles

Nanoparticles of cerium-doped yttrium aluminum garnet (YAG:Ce3+) phosphors were synthesized by a nonhydrolytic solvothermal method yielding particle sizes less than 10 nm. Oleic acid and oleylamine effectively capped the nanoparticles during the synthesis and allowed crystallization of garnet to take place at 300 °C. This facile approach will find wide acceptance and could be used in synthesizing other complex oxide nanoparticles. Studies on electron−phonon interactions in the nanoparticles have been carried out by fitting the observed optical spectra with the multimode Brownian oscillator model. Compared to the same material of larger particle sizes (30 nm, 250 nm, and bulk), the electron−phonon coupling strength is found to be much weaker.

Photoluminescent and crystalline properties of Y3−xAl5O12:Cex3+ phosphor nanofibers prepared by electrospinning

Cerium-doped yttrium aluminum garnet (YAG:Ce3+; Y3−xAl5O12:Cex3+) phosphor nanofibers were successfully prepared using an electrospinning method followed by a heating process. Aluminum nitrate nonahydrate, yttrium nitrate hexahydrate, and cerium nitrate hexahydrate dissolved in dimethylformadide, poly(vinyl pyrrolidone), and ethanol comprised the precursor. The precursor was electrospun under atmospheric conditions to obtain the as-prepared fibers, which consisted of salts and the polymer composite. The as-prepared fibers were then heated to remove the polymer and to obtain the YAG:Ce3+ crystalline fibers. The morphology of the final fibers was homogeneous; the fibers were approximately 300 nm in diameter and several centimeters in length. The photoluminescence (PL) and crystalline properties of the fibers were studied as a function of both the doping fraction (0.005≤x≤0.4) and the heating temperature (900–1400 °C). High heating temperatures resulted in a high degree of crystallinity, crystallites that ranged from 20 to 55 nm in size, and enhanced PL intensity. A doping concentration of 1% (x=0.01) gave the highest PL intensity under excitation at 470 nm. The PL spectra were centered at 530 nm due to the transition from the 5d state to the 4f state (A21g→F25/2 and A21g→F27/2).

Methods of Increasing Luminous Efficiency of Phosphor-Converted LED Realized by Conformal Phosphor Coating

White light output was realized through combining a cerium-doped yttrium aluminum garnet (YAG:Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ) phosphor with a gallium nitride (GaN)-based blue light-emitting diode (LED). In order to coat a phosphor layer of high quality on a GaN chip, the slurry coating technique was applied and investigated because of the coating efficiency and uniformity. The phosphor layer of conformal structure was realized on the LED chip with the self-exposure method. The influences of ammonium dichromate (ADC) as photosensitizer of photoresist in the slurry are discussed. Two methods are brought forward to reduce the absorption of Cr ions introduced by ADC. And experimental results indicate that these two methods are feasible to increase the luminous efficiency of white LEDs.

Preparation and properties of nanocrystalline powders in (Y 1−xCe x) 3Al 5O 12 system

Nano-sized cerium-doped yttrium aluminum garnet (YAG:Ce) phosphors were synthesized via a simple sol–gel process using metal nitrate precursors. The prepared phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy, respectively. Pure cubic garnet phase was formed at temperatures ∼900 οC. The particle sizes of as-prepared powders were mostly in the range of 17–27 nm. The crystalline YAG:Ce showed broad emission peaks in the range of 400–700 nm and maximum intensities at 500 and 520 nm. It is found also that the emission intensity decreased with increasing Ce doping concentration from 0.1 to 1.5 at%. With increasing Ce doping concentration, the PL intensity was shifted towards shorter wavelengths.

Preparation of YAG:Ce spheroidal phase-pure particles by solvo-thermal method and their photoluminescence

Abstract Cerium-doped yttrium aluminum garnet (YAG:Ce) powder was synthesized by a solvo-thermal method under mild conditions with inexpensive aluminum and yttrium nitrates as the starting materials and the ethylenediamine (EDA) solution as the solvent. The formation of YAG:Ce was determined by X-ray diffraction (XRD) techniques and FT-IR spectra. The pure YAG crystalline phase was formed after solvo-thermal treatment at 200 °C for 5 h and no intermediate phase was observed. Transmission electronic microscope (TEM) and scanning electronic microscope (SEM) images showed that the resultant YAG:Ce powders were basically spherical and well dispersed. The sizes of the grains were in the range of 200–260 nm. The photoluminescence spectrum of the crystalline YAG:Ce phosphors showed the green-yellow emission with 5d → 4f transition was the most prominent, and the excitation and emission intensities enhanced with prolonging the holding time.

Synthesis and characterization of photoluminescent cerium-doped yttrium aluminum garnet

Powder phosphor yttrium aluminum garnet (YAG), doped with trivalent cerium (Ce 3+) is synthesized by sol–gel method. The formation of YAG and YAG:Ce (cerium-doped yttrium aluminum garnet) was investigated by means of X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were also used. The purified crystalline phases of YAG and YAG:Ce were obtained at 1000 °C. The maximum average grain size is about 20–23 nm for undoped samples and 28–34 nm for doped samples. The crystalline YAG:Ce emission shows one peak in the range 480–535 nm with the maximum near 520 nm. Photoluminescence (PL) intensity of 5d → 4f transition of Ce 3+ increased with increasing annealing temperature. With increasing the concentration of Ce 3+, the photoluminescence peak shifts towards the red region.

Development of SiAlON - From Mechanical to Optical Applications

Various rare-earth-doped α-SiAlON powders with high purity were prepared to study mechanical and optical properties of SiAlON-based functional materials in connection with ionic radius and electronic structure of rare-earth elements. Single phase rare-earth-doped α-SiAlON powders were obtained at a temperature as low as 1873 K by heating powder mixtures of rare-earth oxide, AlN and highly active ultrafine amorphous Si3N4. Bending strength of highly dense rare-earth-doped α/β-SiAlON-based ceramics was increased with decreasing radii of rare-earth ions, i.e., Yb-SiAlON-based ceramics exhibited excellent high-temperature strength and oxidation resistance caused by the small ionic radius of ytterbium. As for optical application, α-SiAlON is an excellent host lattice with good thermal and chemical stability for doping rare-earth element which activates photoluminescence. Europium-doped Ca-α-SiAlON phosphor formulated as CaxEuy(Si,Al)12(O,N)16 (where 0&lt;x+y&lt;2) was prepared to obtain high quality phosphor with high brightness and desired emission characteristics. Photoluminescence spectra of the resultant Europium-doped Ca-α-SiAlON exhibited high emission intensity at peak wavelength of 580-600 nm giving the better yellow color tone than Cerium-doped yttrium aluminum garnet for applying white LED. It was demonstrated that nitrides or oxynitrides were the innovative materials for the diverse range of high performance specialty applications.

Photoluminescence in sol–gel-derived YAG:Ce phosphors

Cerium-doped yttrium aluminium garnet (Y 3Al 5O 12, YAG) microcrystals were grown using sol–gel technique. The samples were characterized by application of X-ray diffraction (XRD), photoluminescence (PL) spectroscopy and frequency-domain fluorescence lifetime measurements. The PL output, which is important for wavelength conversion in white light emitting diodes (LEDs), was studied as a function of Ce content and annealing temperature. XRD analysis evidenced that sintering of polycrystalline Y 3Al 5O 12:Ce powders at 1000 °C results in the formation of monophasic garnet materials up to 10 mol% of Ce doping; however, concentration quenching is observed in samples with the Ce content exceeding ∼4% probably due to optical losses in the tail states of the imperfect lattice. PL output increased and the concentration quenching disappeared when a higher sintering temperature of 1300 °C was used. However, in high Ce content (>4%) samples, the increase in sintering temperature was found to result in the formation of CeO 2 phase accompanied by an uncontrolled bouncing of PL intensity in powders with similar Ce content.

Synthesis of nano-scaled yttrium aluminum garnet phosphor by co-precipitation method with HMDS treatment

The present paper describes the process of preparing nano-scaled and well-crystallized cerium-doped yttrium aluminum garnet (YAG:Ce) crystalline phosphors synthesized by co-precipitation method with the addition of hexamethyldisilazane (HMDS) as OH-scavenging reagent. Thermal analyzer and X-ray diffractometer measurements showed that pure YAG phase could be got at the temperature of 900 °C lower than that by solid-state method. It was also found that smaller size crystallites (∼33 nm) were made after the HMDS treatment under the transmission electron microscope (TEM) observation. We inferred that it was achieved by reducing the surface condensing hydroxyl groups and by restricting the grain boundary motion due to second-phase particles pinning. Meanwhile, optical properties of YAG:Ce prepared in the present work were examined and showed that the photoluminescence intensity of the co-precipitated YAG:Ce crystallites plus HMDS treatment was better than those prepared by solid-state reaction or co-precipitation without any further treatment. It was proposed that the existing second-phase particles as well as higher specific surface area of nano-scaled YAG:Ce crystallites enhance the absorption of excitation.

Spectroscopic analysis of proton induced fluorescence from cerium doped yttrium aluminum garnet

We have determined the effect of proton induced damage on relative scintillation efficiency for yttrium aluminum garnet doped with cerium (YAG:Ce). The YAG:Ce phosphor samples were exposed to a 3 MeV proton beam, and substrate temperature was limited to control heating damage. Real time in situ measurements of the fluorescence spectra permitted observation of the spectral characteristics of scintillator deterioration due to particle induced damage. Fluorescence from YAG:Ce is relatively dim when compared to other rare earth oxysulfide compounds and the light intensity drops rapidly with dose. Spectra from proton irradiated YAG:Ce exhibit a broad fluorescence peak that is much wider than is typical in other yttrium and gadolinium phosphor compounds. The physical processes in YAG:Ce are very different from other bright-line phosphors as shown by the large difference in the observed fluorescence peak width. Light intensity decreases with dose, following the Birks and Black empirical model.

Defect-property correlations in garnet crystals. VI. The electrical conductivity, defect structure, and optical properties of luminescent calcium and cerium-doped yttrium aluminum garnet

The electrical and optical properties of calcium and cerium-doped yttrium aluminum garnet (Ca,Ce:YAG) have been studied. Ca,Ce:YAG is a mixed ionic and electronic conductor with an ionic conductivity activation energy of 4.3 eV. Evidence of cluster formation with a consequent higher-than-expected activation energy is presented. The cerium normally enters the crystal as Ce+4, but it may be converted to Ce+3 under reducing atmospheres at elevated temperatures.

A Non-Radiative Energy Transfer Model for Cerium-Doped Yttrium Aluminium Garnet (Ce: YAG)

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Defect luminescence in cerium-doped yttrium aluminum garnet

The absorption and photoluminescence of lattice defects and of the cerium ion (Ce+3) in cerium-doped yttrium aluminum garnet have been measured after annealing single crystals of this material in various reducing atmospheres. The absorption in the 200–300-nm wavelength range is observed to decrease as the partial pressure of oxygen (PO2) in the annealing atmosphere decreases, while both the cerium emission at 550 nm and the lattice defect luminescence at 300 nm increases. The lattice defect emission appears to be associated with electrons located on oxygen vacancies.

Defect-property correlations in garnet crystals: The electrical conductivity and defect structure of luminescent cerium-doped yttrium aluminum garnet

The conduction mechanisms in cerium-doped yttrium aluminum garnet (Ce:YAG) have been studied as a function of temperature and PO2. ac conductivity and ionic transference measurements show that Ce:YAG is a mixed ionic-electronic conductor with an ionic conductivity characterized by an activation energy of 2.3 eV. A derived thermal band-gap energy of 6.1 eV compares favorably with the optically measured band gap. Conductivity and transference measurements support a defect model with a fixed number of doubly-ionized oxygen vacancies as the primary defect; the energy to produce such vacancies is calculated to be 7.8 eV.

Optical studies of cerium doped yttrium aluminum garnet single crystals

Single crystals of undoped and cerium-doped yttrium aluminum garnet have been pumped with laser radiation of 220- and 266-nm wavelength. A broadband defect emission at approximately 300 nm was observed, similar to that obtained with cathodoluminescence, although decreased in magnitude. Evidence of a transfer of energy from these defect states to the Ce+3 states was inferred from the photoluminescence decay time measurements. We have associated the absorption spectra from 200–300 nm with the defect excitation spectrum, including the peaks at 225 and 270 nm.

A high luminance high-resolution cathode-ray tube for special purposes

For those applications where light sources of high radiance or displays of high resolution are necessary, miniature cathode-ray tubes have been developed with monocrystalline luminescent screens. These newly developed screens consist of cerium-doped yttrium-aluminum garnet (YAG), epitaxially grown on commercially available YAG substrates; they have an excellent heat conductivity and are optically clear. The construction of the tube and its performance in two modes of operation are described. When the tube is operated with a continuous undeflected beam, the luminance of the spot is limited by thermal quenching of the phosphor material. Under these circumstances, the maximum luminance of 1.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> cd/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (0.55 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> FTL or 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> sr) is reached at a power of 70 mW in a 3.5-µA 20-kV beam, focussed to a spot of 9 µm diameter. Equipped with appropriate deflection coils and scanned with an interlaced field of 575 active lines and 25-Hz repetition frequency, the tube can handle up to 20 W of beam power in a 12 × 16 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> image area. In this mode, the luminance is limited by the design of the electron gun and the desired resolution. At 20 kV and 100 µA (i.e., at 7500 cd/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) the tube has a half-intensity linewidth of 60 µm, which is equivalent to 500-TV limiting response lines in the same 12 × 16 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area.