Luminescent Ceramics Research Articles

Reactive spark plasma sintering and luminescence properties of Gd2O2S:Tb nanocrystalline phosphor

Gd2O2S:Tb is promising for energy-efficient lighting and display applications. This work explores the use of reactive spark plasma sintering (SPS) to synthesis Gd2O2S:Tb nanocrystalline phosphor. It allows to significantly simplify the technological process in comparison with traditional multi-stage liquid-phase synthesis. As-sintered Gd2O2S:Tb demonstrated average crystallite size of 26 nm and secondary particle size of 26 μm. Bright green emission occurs at 545 nm under UV excitation of 245 nm. Average fluorescence lifetime was 0.656 ms. Further consolidation of the Gd2O2S:Tb prepared via reactive SPS can also be expected to yield highly dense ceramics. The innovative reactive synthesis strategies provide valuable insights into the design and development of high-performance luminescent ceramics.

Structure, microstructure, mechanical and luminescent properties of (Y0.96Еu0.01Sm0.01Tb0.01Er0.01)NbO4 ceramics obtained by uniaxial hot pressing

Fine powders of yttrium orthoniobate activated by Eu, Sm, Tb, Er have been synthesized by the sol-gel. The synthesized powders have been calcined at different temperatures (1000, 1100 and 1180 °C). Luminescent ceramics (Y0.96Еu0.01Sm0.01Tb0.01Er0.01)NbO4 were prepared from fine powders by uniaxial hot pressing (UHP) via various technological modes. For the first time, the crystal structure, microstructure, spectral composition, photoluminescence properties of (Y0.96Еu0.01Sm0.01Tb0.01Er0.01)NbO4 ceramics have been studied depending on the temperature conditions of the synthesis of powders and UHP conditions during sintering of ceramics. The mechanical properties of these ceramics (Young's modulus, microhardness and critical stress intensity factor for the mode I KIC) have been evaluated.

Enhanced efficiency and thermal performance of multistage gradient doping Ce:YAG transparent ceramics for laser lighting

The key to realizing the applications of ceramic based laser lighting devices depends on the heat management capability of color converters. In order to sufficiently absorb the blue light and smoothen the temperature gradient of luminescent ceramics, multistage gradient doping Ce3+:Y3Al5O12 (Ce:YAG) transparent ceramics (TCs) with five different concentrations were designed, including 0.01 at%, 0.05 at%, 0.1 at%, 0.2 at% and 0.4 at% Ce. The composite green bodies were prepared by aqueous tape casting and multistage gradient doping Ce:YAG TCs, with concentrations from low to high, were fabricated by vacuum sintering. The in-line transmission values at 800 nm of composite structure Ce:YAG TCs could reach 80.3%. Under 21.13 W/mm2 blue laser excitation, the gradient doping Ce:YAG TC (1.32 mm) realized a high luminous efficacy of 280.3 lm/W, which was 15.8% higher than that of 0.15 at% Ce:YAG TC (240.27 lm/W). Finally, during lighting process, the input-output temperature differences (Tin-Tout) between excitation surface and light-exit surface of 0.15 at% Ce:YAG TC was 5 ℃, while that in gradient doping TC reduced by 50% (2.5 ℃). The results indicate that the multistage gradient doping Ce:YAG TCs will be an interesting color converter for high-power and energy-saving laser-driven lighting.

Tunable yellow and orange emission of Ce, Eu doped multilayered YSZ/YAG ceramics

Eu3+ and Ce3+ doped YSZ/YAG multilayered luminescent ceramics were consolidated by the Spark Plasma Sintering (SPS) method. The optimal modes were explored during the SPS process for functionally graded ceramics (FGCs) structure fabrication. The introduction of rare-earth (RE) oxides into FGCs with different concentration leads to a shift in the temperature range of intense shrinkage to lower temperatures from 1280 °C to 1100–1190 °C and a decrease in the relative shrinkage during the SPS process by 3–6%. Morphological, optical and luminescent properties have been investigated in detail for fabricated YSZ/YAG ceramics with different arrangement of the layers. The nature of luminescent centers in FGCs was studied using time-resolved cathodoluminescent and steady-state photoluminescent (PL) spectroscopy. The PL efficiency of YSZ/YAG ceramics were analyzed and optimal compositions of the FGCs layers were determined. The YSZ/YAG novel functional multilayered ceramics could be promising candidate for light-emitting devices application.

Optical and Electrical properties of KNN-SBN:Ho/xYb Transmittance Luminescent Ferroelectric Ceramics

Transparent luminescent ceramics 0.94(K0.5Na0.5)NbO3-0.06Sr(Bi0.5Nb0.5)O3: 0.1Ho2O3/xYb2O3 (KNN-SBN:Ho/xYb, x=0.5, 1.0, 1.5, 2.0) have been synthesized using a solid-state reaction method.All the ceramic materials exhibit a pseudo-cubic structure without heterogeneous phases at room temperature. In addition, the microstructure of KNN-SBN:Ho/xYb transparent luminescent ceramics is very dense, and at the same time, good optical transparency is obtained, with a transmittance of 70.19% when x is 0.5. KNN-SBN:Ho/xYb transparent luminescent ceramics exhibit upconversion luminescence properties, and the best upconversion luminescence intensity is obtained when x is 1.5. The KNN-SBN:Ho/xYb transparent luminescent ceramics are ferroelectrics with good ferroelectric properties under an applied electric field of 120 kV·cm−1, and the maximum polarization intensity is the highest when x is 0.5, which is 21.32 μC·cm−2.

Organic hybrid tetranuclear clusteroluminogens: Blue-light-excitable LED with ultrahigh luminous efficacy

The development of highly emissive luminescent materials is vital for future light-emitting diodes, display, and scintillation applications. A series of novel organic hybrid metal halide clusters are presented here, that is, non-emission (C4H12N2)3(NH4)4Cd4Cl18 (namely, 1), pink-emission (C4H12N2)3(NH4)4Mn4Cl18 (namely, 2) and 1–2 alloy (namely, Mn-1). The crystal structure of alloy compound provides a clear insight into the Mn(II) effect. Mn(II) alloying in the host lattice successfully induces large octahedral distortion, hybrid of d/p orbitals and lower local symmetry resulting in a breaking d-d forbidden transition. The intense blue light absorption and high PLQY (92.6 %) inspire us to assemble Mn-1 as a blue-light-excited white light-emitting diode (WLED). The WLED has a minimized trade-off among luminous efficacy (182 lm/W), color-rendering index (82) and CCT (4536 K), which is achieved by the trichromatic combination (blue light chip, green (Ba, Sr)2SiO4:Eu2+, red Mn-1) and the red emission edge below 700 nm. The luminous efficacy of 182 lm/W is the highest among the previous WLEDs based on the lead-free metal halides, comparable to the market standard (185 lm/W) in 2020 set by The United States Department of Energy. In addition, the water-soluble Mn-1 further gives potential applications in X-ray scintillators, luminescent ceramics, flexible films and luminescent imaging agents. The discovery of tetranuclear metal halide clusters establishes a new strategy for constructing promising emissive materials.

Silver nanoparticles as a new sintering additive for the fabrication of YAG:Ce optical luminescent ceramics

AbstractIn this study, silver nanoparticles (NPs) were considered for the first time as a sintering additive in the manufacture of YAG:Ce luminescent ceramics. The influence of the addition of silver NPs on the sintering kinetics of ceramics was investigated. It was found that the addition of Ag NPs in the concentration range of 0.027–0.44 wt% does not result in the formation of secondary phases in YAG:Ce ceramics. It was demonstrated that the light transmission of ceramics is dependent on the concentration of Ag NPs. The use of NPs additive has made it possible to increase the light transmission of ceramics compared with the reference sample without sintering additives. The combination of two sintering additives, TEOS and silver NPs, enables the achievement of enhanced optical transparency in ceramics compared to the individual application of sintering additives. At an optimal silver concentration of 0.11 wt%, in combination with 0.5 wt% TEOS, a ceramic light transmission value of 77% was attained. The study has identified a correlation between the luminescence intensity of YAG:Ce ceramics and the concentration of silver NPs. It was observed that the utilization of low concentrations of the Ag additive had negligible impact on the luminescence properties, whereas the introduction of high concentrations of Ag NPs led to a deterioration in the luminescence and optical transparency of the ceramic.

Characterization of YAG:Ce ceramics with graphene oxide

Yttrium-aluminum garnet (Y3Al5O12) is an optical material that shows great potential due to its favorable light-emitting and mechanical properties, as well as its chemical stability and thermal resistance. It is commonly utilized in laser technology, optical instruments, and solid-state light sources as a result of its activation by transition metal or rare earth element ions. In this work, experiments were carried out on the procedure for compacting samples of luminescent ceramics Y3Al5O12:Ce3+, by single-base pressing followed by sintering. Comprehensive studies of the influence of graphene oxide of variable concentration (x=0.1;0.5; 1 wt.%) on the radiative characteristics of ceramic samples. It was found that the addition of graphene oxide in an amount from 0.1 to 1 wt. % affects the density and luminescent properties of YAG:Ce ceramics. There is a decrease in the value of the density parameter at concentrations of graphene oxide 0.1-1 wt. % before annealing, after annealing, the relative density value increases to ~99 %. The luminescence spectrum when excited by a blue LED chip appears as a wide band in the spectral range 460-750, the nature of which is associated with radiative transitions in the cerium ion. It has been established that the light-emitting characteristics have a downward trend when activated by graphene oxide. The integral luminescence intensity decreases from 27.1 % to 19 % with an increase in the concentration of graphene oxide.

Functional design and implementation of multilayer Ce:YAG/Cr:YAG composite transparent ceramics by tape casting for white LEDs/LDs

The shortage of red-light emission in Ce3+:Y3Al5O12 (Ce:YAG) luminescent ceramics is a bottleneck problem to realize the key applications of ceramics based white light-emitting diode (LED) and laser diode (LD) devices. However, the energy band-gap engineering for Ce3+ ion via host substitution or red-emission ions co-doping always leads to its decrease of luminescence efficiency (LE), while a spectrum overlay strategy would be simple and effective. In this study, multilayer composite structure Ce:YAG/Cr:YAG transparent ceramics (TCs) with high color rendering index (CRI) were fabricated by tape casting and vacuum sintering. An organic tape casting protocol with low toxicity and environmental protection was developed and the amounts of dispersants, binders, and plasticizers were systematically optimized to produce good quality tapes with no defects. The transmittance of ceramic reached 78% at 800 nm. By using a 455 nm blue chip, the CRI of the Ce:YAG/Cr:YAG TCs based LED device was increased from 26.7 to 77.5, and the LE was decreased from 181.5 to 10.4 lm/W. Additionally, the optimized LE and CRI for LD device were 130.2 lm/W and 78.1, respectively. Therefore, this research displays that the design and implementation of ceramic functional layer to achieve the essential enhancement of CRI in TC based white lighting is a promising method through the tape casting forming technology.

Sintering and characterization of novel multilayered MgAl2O4/YAG, MgAl2O4/YSZ and YAG/YSZ ceramic-ceramic architectures for photonic applications

During layer-by-layer formation of Y3Al5O12 (YAG), MgAl2O4 (MAS), ZrO2–Y2O3 (YSZ) powders and their consolidation by the SPS method, multilayer YAG/MAS, YSZ/YAG and MAS/YSZ ceramics exhibiting functionally graded properties were synthesized. The morphological, mechanical, optical and luminescent properties have been studied in detail for fabricated ceramics. It is shown that the microhardness of both the ceramics layers and the separate single layers are comparable to each other. The transmission spectra of YSZ/YAG and YAG/MAS ceramics showed correlation with the transmission level prepared from monolayers of starting materials. For MAS/YSZ, this agreement was not found. It has been shown that the pulsed cathodoluminescence spectra of YSZ/YAG, YAG/MAS, and MAS/YSZ with a good agreement of existing luminescence centers nature for YAG, YSZ, and MAS multilayer ceramics. This work provides promising new microstructures in developing novel multilayered luminescent ceramics for photonic applications.

Photopolymerization 3D printing of luminescent ceramics

Photopolymerization 3D printing of luminescent ceramics

KNN–Eu transparent ferroelectrics: Local structure and luminescent property

AbstractDiffer from the rapid development of piezoelectricity in potassium sodium niobate (KNN) ceramics, the progress of photoluminescence in transparent KNN ferroelectric ceramics remains stagnant. Herein, europium (Eu)‐doped KNN ceramics have been prepared to investigate its local structure and optical–electrical multi‐functionality. Both enhanced piezoelectricity in ceramics with a bimodal distribution of grain size and improved luminescent property in ceramics with refined grain size can be achieved by adjusting the content of Eu. The addition of Eu can destroy long‐range ferroelectric orders, leading to the formation of pseudo‐cubic phase and polar nanoregions (PNRs). The highly activated PNRs promoted electric field‐induced domain switching and nearly reversible piezo/ferroelectric properties. First‐principles calculations show that Eu substitution will lead to local inhomogeneous chemical bond environment, affecting the local electric/elastic fields and crystal fields, and then benefiting to the luminescence behavior, including both the intensity and lifetime. We believe that this work can benefit to the development of KNN transparent luminescent ceramics and the light‐emitting devices.

ENHANCING PHOTOMETRIC PERFORMANCE OF YAG:CeCERAMICS: INVESTIGATING THE ROLE OF ANNEALING IN RADIATION-ASSISTED SYNTHESIS

Ceramic samples of cerium-doped yttrium aluminum garnet (YAG:Ce) were successfully synthesized utilizing a high-powered electron flux field with a considerable energy level of 1.4 MeV and a power density of 23 kW/cm2. The ceramics were formed in a remarkable time span of just one second from a specifically prepared mix of yttrium, aluminum, and cerium oxides. The process of radiation-assisted synthesis of ceramics within radiation flux fields fundamentally deviates from the methodologies commonly employed today. Analyzed diffraction patterns closely align with those documented for YAG:Ce crystals, both in peak position and proportion. Furthermore, every sample consistently demonstrated a space group symmetry of Ia-3d. The luminescence and excitation spectra of ceramics synthesized in this study closely resemble those of YAG:Ce ceramics produced by other methods and YAG:Ce -based phosphors. The luminescence bands exhibit high efficiency, and the intensity ratios of the UV bands vary among the studied phosphors. The ceramics' radiation-to-luminescence conversion efficiency was found to be impressive, achieving scores of 0.57 and 0.48 in the industrial phosphors SDL 4000 and YAG-02, respectively. It was also observed that an increase in quantum efficiency of the samples could be achieved via high-temperature annealing. High conversion efficiency underscores the potential of the outlined luminescent ceramics synthesis method.

Fabrication and characterizations of Eu2+‐Dy3+ co‐doped SrAl2O4 ceramics with persistent luminescence

Abstract(Sr0.97Eu0.01Dy0.02)Al2O4 persistent luminescence (PersL) ceramics were fabricated by solid‐state reactive sintering in vacuum combined with hot isostatic pressing (HIP) using H3BO3 as a sintering additive. The phase composition, microstructure, luminescence properties, trap state, and PersL performance of HIP post‐treated (Sr0.97Eu0.01Dy0.02)Al2O4 PersL ceramics were discussed. For the (Sr0.97Eu0.01Dy0.02)Al2O4 PersL ceramics after HIP post‐treatment, the initial luminescence intensity of the ceramics reached over 6400 mcd/m2 with simulated daylight irradiation of 1000 lx for 5 min, and the persistent emission decay time > 17 h. This is much better than the SrAl2O4:Eu2+,Dy3+ PersL powders and the other luminescent ceramics. In addition, this method is a solid‐state reactive sintering method for synthesizing ceramics, which has the advantages of low cost and simple operation, and is suitable for large‐scale, high‐volume industrial production.

Electron Beam-Assisted Synthesis of YAG:Ce Ceramics.

In this work, we present the results of the structure and luminescence properties of YAG:Ce (Y3Al5O12 doped with Ce3+ ions) ceramic samples. Their synthesis was carried out by sintering samples from the initial oxide powders under the powerful action of a high-energy electron beam with an energy of 1.4 MeV and a power density of 22-25 kW/cm2. The measured diffraction patterns of the synthesized ceramics are in good agreement with the standard for YAG. Luminescence characteristics at stationary/time-resolved regimes were studied. It is shown that under the influence of a high-power electron beam on a mixture of powders, it is possible to synthesize YAG:Ce luminescent ceramics with characteristics close to the well-known YAG:Ce phosphor ceramics obtained by traditional methods of solid-state synthesis. Thus, it has been demonstrated that the technology of radiation synthesis of luminescent ceramics is very promising.

Advances of the Cubic Symmetry Crystalline Systems to Create Complex, Bright Luminescent Ceramics

A method to create compositionally disordered compounds with a high number of cations in the matrices, that utilize the cubic spatial symmetry of the garnet-type crystalline systems is demonstrated. Mixtures of the garnet-type powdered materials solely doped with Ce were used to create atomic compositions of high complexity. Several mixed systems, namely Gd3Al2Ga3O12/(Gd,Y)3Al2Ga3O12, Y3Al5O12/Gd3Al2Ga3O12, and Y3Al5O12/Y3Al2Ga3O12 were annealed, compacted and sintered in air. The materials were evaluated for structural, luminescence, and scintillation properties. It was demonstrated that the properties of the resulting ceramics are a little dependent on the granularity of powders when the median particle size is below ~5 μm.

Synthesis and Characterization of Ceramics BaxMg(2 – x)F4 Activated by Tungsten

The possibility of radiation synthesis of luminescent ceramics from a mixture of Ba and Mg fluorides and WO3 oxide is shown for the first time. Synthesis is implemented in a powerful electron beam with an energy of 1.4 MeV by direct exposure of the charge to radiation. It is shown that the characteristic band is observed in the photoluminescence spectrum of the synthesized materials due to the introduction of tungsten, which indicates the incorporation of tungsten into the lattice during radiation synthesis without the use of additional substances in the charge.

Effect of Precursor Prehistory on the Efficiency of Radiation-Assisted Synthesis and Luminescence of YAG:Ce Ceramics

The quality of synthesized materials is affected by various factors such as the prehistory of substances used and the synthesis technology. Most methods for synthesizing luminescent ceramics based on metal oxides rely on high-temperature heating to facilitate the necessary exchange of elements between precursor particles. However, a promising alternative method involves the direct application of a powerful high-energy radiation flux, which stimulates different processes. The formation of ceramics through this method occurs in a highly ionized medium, which may produce different results from those achieved through thermal exposure. This paper reports the findings of a study that explores the relationship between the morphology and luminescent properties of YAG:Ce ceramics and the characteristics of Y2O3 and Al2O3 oxides used in the synthesis, such as dispersity and activator concentration. The results indicate that the morphology of the synthesized ceramic samples is significantly affected by the dispersity of the powder mixture used.

Cs2SnCl6:Bi3+, Te4+ flexibility polysiloxane luminescent ceramics and application

In recent years, lead-free metal halide luminescent materials have attracted extensive attention because of their excellent properties including but not limited to good environmental compatibility, ultrawide emission band, and high photoluminescence quantum yield. They are considered to have great application potential in the photoelectric field. We modified the previously reported synthesis and prepared pure phase Cs2SnCl6 : Bi3 + , Te4 + using simple solution method. Then the emitter was further coated with polysiloxane to form polysiloxane luminescent ceramic (PSOLC). The prepared PSOLCs have almost the same luminescence as the powders, and their color coordinates and color temperature can be tuned freely by adjusting the ratio of blue and yellow emission, which both encourage outdoor-lighting application. Additionally, they are demonstrated to support flexible luminescence and show highly improved machinability. To test their performance in practical application, we apply the PSOLCs to safety identification board and finally get a satisfactory result, directly indicating that the PSOLCs prepared from lead-free perovskite are quite suitable for flexible-lighting-related display applications.

Effect of vacuum sintering conditions on the properties of Y3Al5O12 : Ce luminescent ceramics

The aim of this work was to study the effect of vacuum sintering conditions and cerium concentration on the optical, luminescent and thermal properties of yttrium-aluminum garnet based ceramics doped with Се3+ cations. Series of ceramic powders were synthesized and samples of luminescent ceramics having the composition Y3-хСехAl5O12 were synthesized where x was in the range 0.01 to 0.025 f.u. We show that the phase composition and grain size distribution of the ceramic powders do not depend on cerium concentration. Without sintering additives, an increase in vacuum sintering temperature from 1675 to 1800 °C leads to an increase in the optical transmittance of luminescent ceramic specimens from 5 to 55% at a 540 nm wavelength and an increase in the thermal conductivity of the samples from 8.4 to 9.5 W/(m ∙ K). It was found that an increase in cerium concentration leads to a shift of the luminescent band peak from 535 to 545 nm where as the width of the luminescent band decreases with an increase in vacuum sintering temperature from 1675 to 1725 °C.