Preparation of Neodymium-Doped Yttrium Aluminum Garnet Transparent Ceramics by Homogeneous Precipitation Method

substitutes tion, high loosely dis Neodymium doped-yttrium aluminum garnet （Nd ： YAG） transparent polycrystalline ceramics already become of single crystals because they are provided with easy fabrication, low cost, large size, highly doped concentraheat conductivity, mass fabrication, multi-layers and multi-filnctions. The Nd：YAG precursor powders with persed , slightly agglomerated, super fine and YAG cubic crystal phase were synthesized at 1100 ℃ by the homogeneous precipitation method, using Nd2O3, Y2O3, Al（NO3）3·9H2O and urea as raw materials, （NH4）2SO4 as electrical stabilizer, TEOS as sintering additive. The Nd：YAG transparent ceramics were prepared after being vacuum sintered at 1700 ℃ for 5 h. The Nd：YAG ceramic materials were characterized by the TG-DTA, XRD, FT-IR, TEM, FEG-ESEM and FT-PL. The results show that the crystallization temperature of YAG is 850 ℃ and the intermediate crystal phase YAP forming during the heat treatment transforms to YAG cubic crystal phase at 1050 ℃. The lasing wavelength of （Nd0.01 Y0.99）3Al5O12 transparent ceramics is 1.065 μm and there exists a slight red-shift compared to the single crystal with the same chemical composition. The optical transmittance is 45 % in the visible light and 58 % in the near infrared light and the optical transmittance descends with the decreasing the wavelength.

Novel Phenomenon on Valence Unvariation of Doping Ion in Yb:YAG Transparent Ceramics Using MgO Additives

Yb：YAG nanopowders were synthesized by the alcohol-water co-precipitatlon method adding MgO as sintering additives. Appropriate amount of MgO adding can restrict the agglomeration and reduce the particle size of Yb：YAG powders. When the MgO content was 0.04wt%, well-dispersed Yb：YAG powders with ellipsoidal particles of less than 100 nm diameter were obtained. The experimental results showed the valence variation of doping ion Yb〉 would not appear when adding MgO as sintering additives, so ceramics showed colorless transparent instead of green due to Yb^2＋ color center using traditional SiO2 as additives. The transmission of the sintered Yb：YAG ceramics can reach 80.6% even without annealing. Ceramic morphology showed that the grains had uniform-distribution with the size of 10 iam or so, and no impurity and pore existed in the grain boundary and crystalline while using optimal sintering conditions.

Effects of Sintering Additives on Preparation of CaF_2 Transparent Ceramics

The effects of different sintering addictives on the preparation of CaF2 transparent ceramics were studied. Transparent CaF2 ceramics were fabricated by vacuum sintering and hot isostatic pressing （HIP） method, using CaF2 nanopowders synthesized by chemical precipitation method as raw materials. The nanopowders and transparent ceramics were studied using X-ray diffraction, transmission electron microscopy （TEM）, scanning electron microscopy （SEM） and spectrophotometer. The experimental results indicated that the obtained nanopowders presented normal distribution with grain size about 30 nm; transmittance of CaF2 transparent ceramics was 39% and 26% at 1100 nm for LiF and NaF as sintering addictives, respectively, with corresponding mean grain size 188 μm and 44 μm. Loss of transmission could be attributed to the residual closed porosity. Sintering mechanism was liquid-phase sintering at pre-stage, then solid-phase sintering at later stage, as well as solid solution of lithium ions and sodium ions in the CaF2 lattice structure.

Application of Stereology on Neodymium-Doped Yttrium Aluminum Garnet (Nd∶YAG) Transparent Ceramics

Nd ： YAG precursor powders were synthesized by homogeneous precipitation, and Nd ： YAG transparent ceramics were prepared by vacuum sintering at 1700 ℃ for 5 h. The ceramic materials were characterized by light transmittance and field emission gun-environment scanning microscope. Using statistics and stereology theory, study was carried out on the quantitative relationships between light transmittance and stereological parameters in three-dimensional Euclidean space. It is found that the transmittance of Nd：YAG with 1 mm in thickness is about 45% and 58% in visible and near-infrared wavelength, respectively. The transmittance linearly increases with increasing equivalent sphere diameter and reaches the theoretical value of single crystal when the equivalent sphere diameter is 20μm. The transmittance decreases with the increasing of mean specific area per unit volume of grain and discrete grains, and the transmittance decreases with increasing mean free distance of grains in Nd：YAG ceramics.

Synthesis and Luminescent Properties of LuAG:Ce^(3+) Transparent Ceramics by Solvo-Thermal Method

The precursor powders of LuAG∶Ce3+ transparent ceramics were synthesized by solvo-thermal method.The crystal structure and morphology of powders were analyzed by means of Fourier transform infra-red spectroscopy,X-ray diffraction and scanning electron microscopy.The precursor powders were sintered into transparent ceramics in vacuum and then in nitrogen without any additive.The surface morphology of the transparent unpolished ceramics was characterized using scanning electron microscopy.Some factors that affect the transparency of ceramics were discussed.The UV-Vis fluorescence excitation and emission spectra of LuAG∶Ce3+ transparent ceramics were measured.The vacuum ultraviolet spectra of transparent ceramics were investigated using the synchrotron radiation as the excitation source.The excitation mechanism of Ce3+ was discussed at different excitation wavelength.

Preparation and Upconversion Luminescence of Y_3Al_5O_(12):Yb^(3+),Er^(3+)Transparent Ceramics

YAG： 1% （atom fraction） Yb^3＋ , 0.5% （atom fraction） Er3＋ transparent ceramics were fabricated by the solid state reaction method using high-purity Y2O3, Al2O3, Yb2O3, and Er2O3 powders as starting materials. The mixed powder compact was sintered at 1760 ℃ for 6 h in vacuum and annealed at 1500 ℃ for 10 h in an air atmosphere. The ceramics consisted of about 10μm grains and exhibited a pore-free structure. The optical transmittance of the ceramics at 1064 nm was nearly 80%. Upconversion emissions were investigated on the ceramics pumped by a 980 nm continuous wave diode laser, and strong green emission centered at 523 and 559 nm and red emission centered at 669 nm were observed, which originated from the radiative transitions of ^2H11/2→^4I15/2, ^4S3/2→^4I15/2, and ^4F9/2→^4I15/2 of Er^3＋ ions, respectively.

Application of Fractals on Microstructure of Neodymium-Doped Yttrium Aluminum (Nd∶YAG) Transparent Ceramics

Nd∶YAG precursor powders were synthesized by homogeneous precipitation and Nd∶YAG transparent ceramics were prepared by vacuum sintering at 1700 ℃ for 5 h. The ceramic materials were characterized by light transmittance, field emission gun-environment scanning microscope. Fractal geometry was used to study the quantitative relationships between light transmittance and fractal dimensions of Nd∶YAG transparent ceramics. It was found that the transmittance of Nd∶YAG with 1 mm in thickness was about 45% and 58% in visible and near-infrared region respectively. The microstructures of Nd∶YAG transparent ceramics were obvious fractal characteristic and fractal dimensions depart a little from two-dimension. The light transmittance decreased with increasing of fractal dimension and nonlinear fit curve was y=1350-1185x+269x2 between fractal dimension and light transmittance of Nd∶YAG transparent ceramics.

Damage characteristics of YAG transparent ceramics under different loading conditions

YAG (Y_(3)Al_(5)O_(12)) transparent ceramics have attractive application prospects for transparent armor protection modules because of their excellent light transmittance and anti-ballistic capability. Understanding the fracture behavior and damage mechanism of YAG is necessary for armor design. To explore the damage characteristics of YAG under compression and tension, shock compression and shockless spalling experiments with soft recovery technique are conducted. The spall strength of YAG is obtained and the recovered samples are observed by CT and SEM. It is shown that the macroscopic damage characteristic of YAG under compression is vertical split cracks with oblique fine cracks distributed in the entire sample, while that under tension is horizontal transgranular cracks concentrated near the main spall surface. The cracks generated by macroscopic compression, tension and shear stress extend in similar tensile form at the microscale. The proportion of transgranular fractures on spall surfaces is higher than that of cracks induced by macroscopic compression. Meanwhile, higher loading rate and longer loading duration increase the transgranular fracture percentage.

Comparative spectroscopic investigation of Yb-doped YAG,YSAG and YLaO_3 transparent ceramics

Transparent Yb doped YAG, YSAG and YaLaO3 ceramics are fabricated by using the co-precipitation method. The spectral properties and thermal parameters of these Yb doped cubic phase transparent ceramics are compared, and their different and potential applications are also analysed. The absorption cross-section and the emission cross-section of these ceramics are measured and calculated. The essential properties of these materials especially for the rep-rated pulsed high-energy diode-pumped solid-state lasers are investigated. The results show that Yb doped YAG, YSAG and YaLaO3 are all suitable materials used for diode-pumped solid-state lasers.

Spectral properties of Ce^(3+) doped yttrium lanthanum oxide transparent ceramics

Ce3＋-doped yttrium lanthanum oxide （Y0.9La0.1）2O3 transparent ceramics is fabricated with nanopowders and sintered in H2 atmosphere. The spectral properties of Ce：（Y0.9La0.1）2O3 transparent ceramics are investigated. There appear two characteristic absorption peaks of Ce3＋ ions at 230~nm and 400~nm, separately. It is found that Ce3＋ ions can efficiently produce emission at 384~nm from （Y0.9La0.1）2O3 transparent ceramic host, while the emission is completely quenched in Re2O3 （Re=Y, Lu, La） host materials.

Yb:CaF_(2)-YF_(3)transparent ceramics ultrafast laser at dual gain lines

Yb^(3+):CaF_(2)–YF_(3)transparent ceramics with excellent optical quality was successfully fabricated by hot-pressed method.Pulsed laser properties of this ceramics were investigated for the first time.Laser diode(LD)was applied as the pump source to generate a dual-wavelength mode-locked(ML)laser.The maximum average output power was 310 mW,which represents the highest output power of ultrafast calcium fluoride ceramic laser.The spectrum separated at 1048.9 nm and 1049.7 nm with a total pulse duration of 8.9 ps.The interval period between the beating signals was about 4.3 ps,corresponding to a 0.23 THz beat pulse repetition rate.These results demonstrate its potential in producing dual-wavelength ultrashort pulses.These Yb^(3+):CaF_(2)–YF_(3)ceramics with low-cost and short-preparation period are ideal candidate materials for ultrafast lasers.

Spectroscopic characterization of Yb:Sc_2O_3 transparent ceramics

Yb：Sc2O3 transparent ceramics are fabricated by a conventional ceramic process and sintering in H2 atmosphere. The room-temperature spectroscopic properties are investigated, and the Raman spectrum shows an obvious vibration characteristic band centred at 415 cm-1. There are three broad absorption bands around 891, 937, and 971 nm, respectively. The strongest emission peak is centred at 1.04 μm with a broad bandwidth （11 nm） and an emission cross-section of 1.8×10^-20 cm^2. The gain coefficient implies a possible laser ability in a range from 990 nm to 1425 nm. The energy-level structure shows that Yb：Sc2O3 ceramics have large Stark splitting at the ground state level due to their strong crystal field. All the results show that Yb：Sc2O3 transparent ceramics are a promising material for short pulse lasers.

A strategy for enhancing luminescence thermometry via Ta^(5+)-triggered K_(0.5)Na_(0.5)NbO_(3):Er^(3+)transparent ceramics

Luminescence thermometry is a reliable approach for remote thermal sensing,and extensive studies have been devoted to designing a luminescence thermometer with heightened thermal sensitivity.Herein,we report a promising luminescence thermometric material,Ta^(5+)-substituted K_(0.5)Na_(0.5)NbO_(3):0.003Er^(3+)transparent ferroelectric ceramics.The temperature sensing sensitivity is significantly improved by adjusting the concentration of Ta^(5+)in the material.Specifically,utilizing the fluorescence intensity ratio from the 2H_(11/2) and 4S_(3/2) thermally coupled states of Er^(3+)as a detecting signal within the temperature range of 273–543 K,an optimal maximum absolute sensitivity of 0.0058 K–1 and relative sensitivity of 0.0158 K–1 are achieved for K_(0.5)Na_(0.5)NbO_(3):0.65Ta^(5+)/0.003Er^(3+).Simultaneously,as the concentration of Ta5+increase,a unique evolution of structural phase transitions is observed from orthorhombic to tetragonal and then to cubic.This is accompanied by an improvement in luminescence temperature sensing properties,and the best sensitivity is demonstrated in the cubic-phase region.Intriguingly,a huge change in infrared luminescence properties as a function of temperature is found around the structure transition temperature of the samples.These results indicate a promising potential for achieving highly sensitive thermometry or monitoring phase structure transitions through luminescence thermometry behavior in the K_(0.5)Na_(0.5)NbO_(3) host.

Nd^(3)+:YAG-Al_(2)O_(3) nanocrystalline transparent ceramics with high inflexion concentration quenching of Nd^(3+) prepared by amorphous crystallization

Rare earth ion-doped Y_(3)Al_(5)O_(12)(YAG)-based transparent ceramics have been used as important laser gain media for a long time,yet the doping concentration of active ions is limited due to concentration quenching,wherein the inflexion concentration quenching of Nd^(3+)is recognized as 1.0 at%.In this work,YAG-Al_(2)O_(3) nanocrystalline transparent ceramics with a concentration of Nd^(3+)(O-5.0 at%)were fabricated via amorphous crystallization,and the crystal structure evolution,morphology,and optical properties were systematically investigated by differential scanning calorimetry(DSC),X-ray powder diffraction(XRD),transmission electron microscopy(TEM),magnetic resonation(MAS),nuclear magnetic resonation(NMR),and fluorescence spectroscopy.The doping of Nd^(3+)can promote the transition of Al[5]and Al[6]to Al[14],indicating improvements in the ability of the amorphous material to form Nd^(3+):Y_(2)O_(3)-Al_(2)O_(3) vitrified beads,and 1.5 at%Nd^(3+):YAG-Al_(2)O_(3) nanocrystalline transparent ceramics can be obtained by crystallization at 1050℃ with a matrix composed of YAG and concomitant δ-Al_(2)O_(3) and θ-Al_(2)O_(3).The nanocrystalline transparent ceramics show an internal transmitance of 89.56%at 1064 nm,and the strongest emission peak corresponds to the energy transfer from 4F_(3/2) to 4l_(11/2) of Nd^(3+)with a fluorescence lifetime of 231μs when pumped by an 808 nm laser.Specifically,spectral broadening begins to occur,indicating the onset of concentration quenching,when the concentration of Nd^(3+)exceeds 1.5 at%,substantially higher than the 1.0 at% observed in YAG ceramics.YAG-Al_(2)O_(3) nanocrystalline transparent ceramics obtained by amorphous crystalization can be utilized as the matrix to increase the inflexion point of doping concentration quenching of Nd^(3+),and this material may have great potential as a laser gain medium.

Fabrication of AION transparent ceramics with Si_(3)N_(4) sintering additive

In this paper,Si_(3)N_(4) was used as a novel solid-state sintering additive to prepare AION transparent ceramics with high transparency and flexural strength via the pressureless pre-sintering and hot isostatic pressing(HIP)method at a relatively low HIP temperature(1800℃).The effect of Si_(3)N_(4) content on the phase,microstructure,optical property,and flexural strength was investigated.The experimental results showed that a Si element was homogenously distributed in both pre-sintered and HIPed AION ceramics.The densification enhanced,the grain grew with the increasing Si_(3)N_(4) content in the pre-sintered AION ceramics,and all the samples became pore-free after HIP,which favor transparency.The AION ceramics doped with 0.10 wt%Si_(3)N_(4) had the highest transmittance of 83.8%at 600 nm and 85.6%at 2000 nm(4 mm in thickness),with flexural strength of 404 MPa,which were higher than those of the previous reports.

Elevating photoluminescence properties of Y_(3)MgAl_(3)SiO_(12):Ce^(3+)transparent ceramics for high-power white lighting

Compared with Y_(3)Al_(5)O_(12):Ce^(3+),Y3MgAl3SiO12:Ce^(3+)(YMASG:Ce^(3+))reveals great potential for highpower white lighting with red-shift spectrum.Herein,YMASG:Ce^(3+)transparent ceramics were explored to be synthesized in the air following hot isostatic pressure(HIP)treatment to obtain tunable and optimized optical properties.Then phase purity,microstructure,transmittance,and photoluminescence of YMASG:Ce^(3+)ceramics were investigated.The emission peak of YMASG:Ce^(3+)transparent ceramic can be tuned from 573 to 592 nm with the variation of Ce^(3+)doping concentration.It should be noted that this YMASG:0.2 at%Ce^(3+)transparent ceramic with emission peak at 579 nm under 450 nm excitation exhibits the highest internal/external quantum efficiency(72%/65%).The white LED device using YMASG:0.2 at%Ce^(3+)transparent ceramic with a 0.4 mm thickness demonstrates a luminous efficiency(LE)of 106 lm/W,correlated color temperature of 3158 K,and color coordinate(0.3933,0.3265).Thermal stability can be significantly imporoved by the incorporation of Lu^(3+)in YMASG transparent ceramic,and the Y3-yLuyMgAl3SiO12:0.2 at/Ce^(3+)(y=0-2.5)transparent ceramics were fabricated.The highest thermal stability(88%@150℃of the integrated emission intensity at 25℃)can be achieved wheny=2.5.The maximum LE of 154 Im/W can be obtained from Y_(0.5)Lu_(2.5)MgAl_(3)SiO_(12):0.2 at%Ce^(3+)transparent ceramic.These results indicate that YMASG:Ce^(3+)transparent ceramics with optimized properties can be regarded as an encouraging candidate for highpower white lighting.

Cyan-green-emitting Ca_(3)Sc_(2)Si_(3)O_(12):Ce^(3+)transparent ceramics:A promising color converter for high-brightness laser lighting

Transparent phosphor ceramics have received increasing attention for high-brightness laser lighting,but commercially available phosphor ceramics are currently mainly limited to yellow YAG:Ce and green LuAG:Ce garnets,leaving a“cyan cavity”which is an obstacle to realizing full-color lighting.Achieving new phosphor ceramics capable of filling the cavity is a challenge.Herein,for the first time,cyan-green-emitting Ca_(3)Sc_(2)Si_(3)O_(12):Ce^(3+)(CSS:Ce)transparent ceramics have been successfully developed by two-step sintering technique under vacuum.The as-prepared CSS:Ce ceramics present high relative density of 99.7%and optical transmittance of 71%in the cyan-green spectral region.It exhibits an efficient band emission peaking at 504 nm(under 450 nm excitation)with internal/external quantum efficiency of 91%/62%.Furthermore,it has excellent thermal stability with a thermal quenching temperature(T_(0.5))of 838 K,approximately 100 K higher than that of LuAG:Ce ceramics(738 K).In addition,the CSS:Ce ceramics can withstand blue laser density of 45.6 W/mm^(2)and meanwhile generates cyan-green light with a forward luminous flux of 813 lm and forward luminous efficacy of 162 lm/W.The CSS:Ce transparent ceramics exhibit excellent luminescence performance comparable to the commercial LuAG:Ce ceramics and could be a highly promising color converter for high-brightness laser lighting.

Structural and Luminescent Properties of Mg_(0.25-x)Al_(2.57)O_(3.79)N_(0.21):xMn^(2+)Green-Emitting Transparent Ceramic Phosphor

A series of spinel-type Mg_(0.25-x)Al_(2.57)O_(3.79)N_(0.21):xMn^(2+)(MgAlON:xMn^(2+))phosphors were synthesized by the solid-state reaction route.The transparent ceramic phosphors were fabricated by pressureless sintering followed by hot-isostatic pressing(HIP).The crystal structure,luminescence and mechanical properties of the samples were systematically investigated.The transparent ceramic phosphors with tetrahedrally coordinated Mn^(2+)show strong green emission centered around 515 nm under blue light excitation.As the Mn^(2+)concentration increases,the crystal lattice expands slightly,resulting in a variation of crystal field and a slight red-shift of green emission peak.Six weak absorption peaks in the transmittance spectra originate from the spin-forbidden ^(4)T_(1)(^(4)G)→^(6)A_(1) transition of Mn^(2+).The decay time was found to decrease from 5.66 to 5.16 ms with the Mn^(2+)concentration.The present study contributes to the systematic understanding of crystal structure and properties of MgAlON:xMn^(2+)green-emitting transparent ceramic phosphor which has a potential application in high-power light-emitting diodes.

Red-emitting YAG:Ce,Mn transparent ceramics for warm WLEDs application

A series of YAG:Ce,Mn transparent ceramics were prepared via a solid-state reaction-vacuum sintering method.The effects of various Mn^2+–Si4+pair doping levels on the structure,transmittance,and luminescence properties were systematically investigated.These transparent ceramics have average grain sizes of 10–16μm,clean grain boundaries,and excellent transmittance up to 83.4%at 800 nm.Under the excitation of 460 nm,three obvious emission peaks appear at 533,590,and 745 nm,which can be assigned to the transition 5 d→4 f of Ce^3+and 4 T1→6 A1 of Mn^2+.Thus,the Mn^2+–Si4+pairs can effectively modulate the emission spectrum by compensating broad orange-red and red spectrum component to yield high quality warm white light.After the optimized YAG:Ce,Mn transparent ceramic packaged with blue light-emitting diode(LED)chips,correlated color temperature(CCT)as low as 3723 K and luminous efficiency(LE)as high as 96.54 lm/W were achieved,implying a very promising candidate for application in white light-emitting diodes(WLEDs)industry.

High performance of La-doped Y2O3 transparent ceramics

As an optical material,Y2O3 transparent ceramics are desirable for application as laser host materials.However,it is difficult to sinter and dense of Y2O3 hinders the preparation of high-quality optical ceramics via traditional processes.In this work,we use La2O3 as a sintering aid for fabricating high-transparency Y2O3 ceramics using a vacuum sintering process.It is demonstrated that the in-line optical transmittance of 15.0 at%La-doped Y2O3 at a wavelength of 1100 nm achieves a transmittance of 81.2%.A sintering kinetics analysis reveals that a grain-boundary-diffusion-controlled mechanism dominates the faster densification at high La3+concentrations.It is also shown that both the mechanical and thermal properties of Y2O3 transparent ceramics are significantly improved upon the increase of La2O3 sintering additives.The results indicate that a La-doped Y2O3 transparent ceramic is a promising candidate for a laser host material.