Luminescent Ceramics Research Articles

3D printed ceramic phosphor and the photoluminescence property under blue laser excitation

An Al2O3/YAG: Ce3+ ceramic phosphor was fabricated for high-flux laser lighting using the digital lighting process (DLP)-based 3D printing method for the first time. The photocurable ceramic suspension for 3D printing was prepared by blending well-treated Al2O3/YAG: Ce3+ composite powders with photosensitive resin monomers and photo-initiators. The printing parameters, debinding and sintering processes were designed delicately to fabricated the dense sub-millimeter-sized cylinder ceramic with high dimensional accuracy. The ceramic showed excellent luminescence property under blue laser excitation with a threshold of 20.7 W/mm2, higher than that prepared via dry-pressing followed by vacuum sintering. The luminescence properties and the microstructures of both ceramics were further comparatively investigated to find the possible interpretations for improvement of laser flux for the 3D-printed ceramic. The present work indicated that the new developed 3D printing method was promising for preparing luminescent ceramics for high-flux laser lighting in a rapid, effective, low-cost and precision-controlled manner.

Spectrum regulation of YAG:Ce transparent ceramics with Pr, Cr doping for white light emitting diodes application

YAG:Ce transparent ceramics with high luminous efficiency and color render index were prepared via a solid state reaction-vacuum sintering method. Cr3+and Pr3+ were applied to expand the spectrum of YAG:Ce transparent ceramics. As prepared ceramics exhibit luminescence spectrum ranging from 500nm to 750nm, which almost covers full range of visible light. After the concentration optimization of Ce3+, Pr3+ and Cr3+, high quality white light was obtained by coupling the YAG:Ce,Pr,Cr ceramics with commercial blue LED chips. Color coordinates of the YAG:Ce,Pr,Cr ceramics under 450nm LED excitation vary from cold white light to warm white light region. The highest luminous efficiency of WLEDs encapsulated by transparent YAG:Ce,Pr,Cr ceramic was 89.3lm/W, while its color render index can reach nearly 80. Energy transfers between Ce3+→Pr3+ and Ce3+→Cr3+ were proved in co-doped ceramic system. Transparent luminescence ceramics accomplished in this work can be quite prospective for high power WLEDs application.

Manufacture of luminescent ceramics by vacuum sintering of nanopowder oxides

A method of nanopowder sintering in vacuum with the presence of carbon was used to manufacture oxygen-deficient Al2O3 and MgO luminescent ceramics. They were sintered at varying temperatures and annealing time. It was shown that during sintering in vacuum, the phase composition, microstructure and luminescent properties of the ceramics change. In the obtained ceramics, the spectra of pulse cathodoluminescence and photoluminescence as well as thermoluminescence glow curve are registered. The luminescence intensity grows with increasing temperature and sintering time. The photoluminescence spectrum significantly changes in the ceramics doped with chromium during sintering. The oxygen-deficient ceramics synthesized in vacuum are promising for applications in optical electronics and solid state dosimetry of ionizing radiations.

Fabrication and photoluminescence of Eu-doped KNN-based transparent ceramics

Transparent lead-free luminescent ceramics K0.47Na0.47Li0.06Nb0.94Bi0.06O3–Eu x (KNNLB:Eu) have been fabricated via hot-press sintering technology. The formation of perovskite KNNLB:Eu ceramics with highly densified microstructure was verified through X-ray diffraction and scanning electron microscopy studies. The transmittance spectra, photoluminescence excitation and emission spectra, dependence of the photoluminescence intensity on Eu3+ doping content as well as the luminescence decay curves were investigated. The KNNLB:Eu ceramics present high transmittance both in the near-infrared and the middle-infrared regions, and can be efficiently excited by near-ultraviolet and blue light to realize strong reddish luminescence. The red emission at around 613 nm is particularly intense, which is attributed to the electric dipole transition 5D0–7F2 of Eu3+. The PL properties are also discussed. The emission peak splitting of 5D0–7F2 transition is observed as a response to the change in crystal environment around Eu3+ in the KNNLB:Eu ceramics. With the novel intrinsic ferroelectric properties of KNN, the KNNLB:Eu ceramics could be promising candidates for multifunctional optoelectronic devices.

Synthesis of luminescent ceramics from alumina nanopowder

The effect of the conditions of high-temperature synthesis in a reducing medium on the density, area and cathodoluminescence of ceramics made of compacted α-Al2O3 powder is the focus of this work. The dependence of the luminescence intensity on the temperature and duration of the synthesis of ceramics is presented. The optimal parameters for synthesis of luminescent ceramics from alumina nanopowder are defined.

Highly sensitive nonlinear luminescent ceramics for volumetric and multilayer data carriers

The interaction of optical ceramics based on wide-band-gap crystals with near-IR femtosecond laser radiation is studied experimentally. The formation of luminescent centres in LiF and ceramics under the action of single laser pulses is considered. Two interaction regimes are used. In the regime of low-aperture focusing of laser radiation , multiple self-focusing and filamentation in the samples are observed. The luminescent centres are formed in thin channels induced by light filaments. The average effective self-focusing length is ; the formation of luminescent centres begins at this length and ceases at a wavelength of about . The luminescent trace (spur) induced by a single laser filament was long and in diameter. The second regime of light interaction with the sample was based on high-aperture focusing with a simultaneous decrease in the laser pulse energy. This led to the formation of single pits with a diameter smaller than the optical diffraction limit. The luminescent centres induced by the laser radiation were aggregated colour centres. The mechanism of their creation included the highly-nonlinear generation of electron – hole pairs in the filamentation region, their recombination with the formation of anion excitons and the decay of excitons into Fresnel defects by the Lushchik – Vitol – Hersh – Pooley mechanism, as well as their recharging, migration and aggregation.

Traps Formation and Characterization in Long-Term Energy Storing Lu2O3:Pr,Hf Luminescent Ceramics

Sintered ceramics of Lu2O3:Pr,Hf storage phosphor were prepared and their spectroscopic properties were evaluated. It was shown that during irradiation with X-rays as well as with short UV radiatio...

Enhanced long lasting persistent luminescent SrAl2O4:Eu,Dy ceramics prepared by electron beam bombardment

Eu and Dy codoped strontium aluminate persistent luminescent (SrAl2O4:Eu,Dy) ceramics is prepared by E-beam bombardment. Surface morphology, crystalline structure, chemical composition, photoluminescence, and the decay characteristic were characterized by SEM, XRD, EDS, and the photoluminescence spectrometers, respectively. The results showed that, E-beam bombardment is a very efficient method to prepare persistent luminescent SrAl2O4:Eu,Dy ceramics, in which Eu3+ is reduced into Eu2+ without the help of any other reducing agents. This method is environmentally friendly, energy and time saving way to prepared oxide ceramics. The afterglow time of E-beam sintered SrAl2O4:Eu phosphor prepared by this method can be extended as long as 72 h.

Upconversion fluorescence studies of sol–gel-derived Er-doped KNN ceramics

Er-doped K0.5Na0.5NbO3 luminescent ceramics have been prepared using a sol–gel method. The results of X-ray diffraction show that Er3+ diffuses into the K0.5Na0.5NbO3 lattices, forming an orthorhombic-structured perovskite. Under an excitation of 980 nm, the ceramics exhibit luminescent emission bands at 527 nm (green), 548 nm (green), 660 nm (red) as well as 487 nm (blue), which are attributed to the transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2 → 4I15/2 and 4F7/2 → 4I15/2, respectively. Our Raman results also reveal that the ceramics have low phonon energy (∼860 cm−1) and thus slow multi-phonon relaxation rate. The sol–gel process and Er3+-doping can produce ceramics with better compositional homogeneity as well as finer and uniform grains. All these are beneficial for improving both the upconversion and luminescent efficiencies of the ceramics, and thus leading to very strong green emissions even at a low quenching concentration of 2 mol%. These suggest that even without using sensitizers, the sol–gel-derived Er-doped KNN ceramics are promising candidates for multifunctional optoelectronic applications.

Controlled synthesis, formation mechanism and lumincence properties of novel 3-dimensional Gd2(MoO4)3:Eu3+ nanostructures

Orthorhombic Gd2(MoO4)3:Eu3+ nanosized particles with complex 3D self-assembled superstructures (dumbbell) were successfully synthesized by a hydrothermal method in ethyleneiamine tetra-acetic acid (EDTA) mediated processes. The pH value, reaction time, temperature, ando molybdenum source have crucial influence on the growth mechanism, shape evolution, and nanostructures. In the hydrothermal process, EDTA not only acts as a chelating reagent to facilitate the formation of Gd2(MoO4)3:Eu3+, but also acts as a surface capping agent to adhere to the newly created surface and to promote the crystal splitting. Comprehensive structural, morphological studies like X-ray diffraction, scanning and transmission electron microscopy were employed to characterize the as synthesized nanostructures. Photoluminescence studies on Gd2(MoO4)3:Eu3+ showed strong red emission upon UV illumination, and this implied potential application in the field of luminescent nano ceramics.

The formation of MgZnO luminescent ceramics

MgxZn1−xO is a promising alloy system with UV-tunable bandgap. The alloy can have the hexagonal or cubic structure depending on the composition x and growth conditions. We present studies of the optical and material properties of Mg0.1Zn0.9O and Mg0.6Zn0.4O sintered ceramics. The rationale for choosing these compositions is that alloys of both the wurtzite and the cubic phases, respectively, can be investigated. To study the alloying dynamics for the optimization of light emission, the properties as a function of annealing temperature in the range of 600–1,100 °C were investigated via micro-photoluminescence, X-ray diffraction, and imaging techniques. For the Mg0.1Zn0.9O it was found that a threshold temperature of ~900 °C is required in order to initiate the formation of the solid solution with the wurtzite structure. At the elevated temperature regime, the photoluminescence energy for this ceramic sample shifted from 3.25 to 3.5 eV, while the ceramic retained the wurtzite structure. The Mg0.6Zn0.4O was found to have a sequence of phases: initially the alloy formed with the wurtzite structure, and then a transition into the NaCl cubic structure took place. Similar to the Mg0.1Zn0.9O, a threshold temperature of ~900 °C was required in order to initiate the alloying process. At that temperature regime an alloy was formed with the wurtzite structure, and its photoluminescence energy was ~3.25 eV. At ~1,100 °C the alloy was found to undergo a phase transition from wurtzite to cubic structure. The photoluminescence energy at that temperature was considerably shifted into the UV-range of 4 eV.

Luminescent Ceramics for Phosphor Converted LEDs

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Nanostructured alumina particles synthesized by the Spray Pyrolysis method: microstructural and morphological analyses

Ultrafine particles or nanoparticles (ranging from a few nanometers to 100 nm) are of considerable interest for a wide variety of applications, ranking from catalyst to luminescence ceramics, due to their unique and improved properties primarily determined by size, composition and structure. This study presents the preparation and characterization of nanostructured spherical alumina particles by the Spray Pyrolysis method for the application in reinforcements of metal-matrix composites (MMCs). Synthesis procedure includes aerosol formation ultrasonically from alumina nitrate water solution and its decomposition into a tubular flow reactor at 700 °C. The obtained particles are spherical, smooth, amorphous and in non-agglomerated state. Microstructural and morphological analyses were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS) and analytical and high resolution transmission electron microscopy (TEM/HRTEM).

Microstructural and morphological analysis of nanostructured alumina particles synthesized at low temperature via aerosol route

Nanometer-sized particles (1–100 nm) are of considerable interest for a wide variety of applications, ranking from catalyst to luminescence ceramics, due to their unique and improved properties primarily determined by size, composition and structure. In this study, we report a simple, rapid aerosol decomposition process for the continuous synthesis of nanoparticles with adjustable sizes, narrow size distribution, high crystallinity and good stoichiometry. This paper presents the preparation and characterization of nanostructured spherical alumina particles (<500 nm sized) by low temperature aerosol synthesis for the application in MMCs reinforcement. Synthesis procedure includes aerosol formation ultrasonically from alumina nitrate water solution and its decomposition into a tubular flow reactor at 400 °C. Consequently, as-obtained particles are spherical, smooth, amorphous and in non-agglomerated state. The phase crystallization, either into γ-Al 2O 3 or α-Al 2O 3 is promoted by additional thermal treatment ranging between 700 °C and 1300 °C. Detailed phase and structural analyses were carried out using X-ray powder diffraction (XRD), scanning electron microscopy (SEM/EDS) and analytical and high-resolution transmission electron microscopy (TEM/HRTEM).

Effects of Glass Frits on the Properties of Luminescent Ceramics

Sr4Al14O25: Eu2+, Dy3+ luminescent ceramics with high brightness and long afterglow were prepared using glass frits as binders by sintering at lower temperature and air atmosphere. The effects of glass frits on the properties of luminescent ceramics were discussed. The analytical results indicate that the surface structure and adhesion with phosphor are influenced by glass frits and sintering temperature. When sintered at 850°C, the samples with frit1 or frit2 obtained good surface morphology and good adhesion. The sample with frit2 sintered at 850°C yielded the better surface morphology and good adhesion. The sample with frit1 sintering at 850°C possessed the better luminescent properties.

Preparation and characterization of rare-earth-doped Y2O3 luminescent ceramics by the use of reverse micelles

The objective of this project was to study luminescent powders of Y2O3:Eu3+ (5 at%), Y2O3:Tb3+ (5 at%), and Y2O3:Tm3+,Yb3+ (Tm: 2 at%, Yb: 1 at%), prepared by the use of reverse micelles. This report describes the phase stability, crystallite size, and luminescence properties of these powder materials as a function of heat treatment time and temperature. The Y2O3 phase produced during synthesis can be controlled by the heat treatment temperature and time. Monoclinic and cubic phases of Y2O3 are obtainable, with the monoclinic powders produced at the smaller crystallite sizes. Photoluminescence properties of the Y2O3:Eu3+ and Y2O3:Tb3+ were evaluated and sharp emission was observed for the Eu3+ powders at 610 nm and the Tb3+ powders at 544 nm. The maximum emission intensity of both phosphors increased as annealing temperature and time increased. This, however, was not seen for the case of the Y2O3:Tm3+,Yb3+ powders, which exhibited emission at 454 nm. For this phosphor, as heat treatment temperature increased the luminescence intensity decreased.

Soft X-ray spectromicroscopy

In recent years much progress has been made in the field of spectromicroscopy, the combination of spectroscopy with lateral resolution. This method is applicated increasingly to problems in biology, material and surface science. Different technical approaches will be outlined and discussed with respect to their imaging and spectroscopic properties. The scanning soft x-ray microscope at HASYLAB has been equipped continuously with new operating modes and has now the capability to use photoelectrons, photodesorbed ions, luminescence, fluorescence, scattered and transmitted photons for imaging and spectroscopy. Examinations of artificial structures, of luminescent ceramics and crystals and of porous silicon will be presented.

Soft X-ray stimulated luminescence microscopy and spectroscopy on Gd2O2S:Pr3+ and (Y, Gd)2O3:Eu3+ ceramics

Abstract The Hamburg soft X-ray scanning microscope at HASYLAB/DESY has been equipped with detectors for luminescence in the visible and X-ray fluorescence or backscattered radiation. The microscope is operating in the region from 20–1200 eV and uses an elliptical grazing incidence mirror to focus the soft X-rays on a spot of about 1 μm. By varying the energy of the incoming radiation, excitation spectra can be taken from small sample areas (microspectroscopy). Defect structures on polished luminescent ceramics were investigated. The influence of the Gd 4d→4f giant resonance on the luminescence signal is observed in the yield spectra and compared with our calculations.

Optical luminescence spectroscopy with the scanning soft x-ray microscope at HASYLAB/DESY

The first attempt to combine luminescence spectroscopy with scanning soft x-ray microscopy has been realized in our experiment. A new imaging luminescence spectrometer with a Schwarzschild objective was designed and built with a spectral resolution of 1.3 nm in the energy range of 1.6–6.5 eV for this purpose. Some luminescent ceramics have been investigated by using this spectrometer. A high contrast in luminescence micrographs is achieved due to the confocal arrangement of the Schwarzschild system and the microscope. The spectral and microstructural properties of these ceramics could be determined by means of luminescence microspectroscopy and spectromicroscopy.

The conversion of high energy radiation to visible light by luminescent ceramics

The properties of luminescence ceramics which are roughly based on rare-earth doped oxides, oxysulfides, garnets, and silicates have been investigated. The characteristic luminescence data of the ceramics considered, such as emission spectra and decay, are similar to those of corresponding powders or single crystals. However, conversion efficiency, afterflow, and energy resolution are strongly affected by ceramic processing due to its influence on the microstructure, final optical quality, and defect structure. In this connection residual pores and grain boundaries play an important role. For example, the insufficient optical quality of Gd/sub 2/O/sub 2/Sr:Pr,Ce-ceramics is the main reason not only for a reduced light output but also for a rather pronounced degradation of the energy resolution, beyond the merely statistical limit. Consequently, luminescent ceramics, at least in their present form, appear not be suited for spectrometric applications. In the case of scintillation counting, the presented ceramics exhibit rather high decay constants giving low count rates. This drawback can be improved by using activator dopants with faster optical transition. >