The fabrication of Ce3+-doped lutetium oxyorthosilicate (Lu2SiO5:Ce, LSO:Ce) scintillation ceramics was investigated by pressureless sintering starting from synthetic submicrometer polycrystalline LSO:Ce powder. It was found that translucent LSO ceramics were densified successfully with relative density of 99.5% under sintering condition of 1720 °C for 4 h. As-sintered LSO ceramics were pore-free with average grain size of 5 μm and exhibited a translucent state. The broad emission spectra centered at 419 nm of the LSO:Ce ceramics under vacuum ultraviolet (VUV) and UV excitation at room temperature. Under x-ray excitation, the overall emission intensity of obtained LSO ceramics achieved twice of that of bismuth germanium oxide (also known as bismuth germanate) single crystal at room temperature. Under excitation of 356 nm and emission of 420 nm, the luminescence decay time of the obtained LSO scintillation ceramics reached only 21.2 ns. The light yield of the LSO ceramics was 21,300 ph/MeV, which reached 91% of that of LSO single crystal.

Transparent 0.67(Pb1−xLax)(Mg1/3Nb2/3)O3–0.33(Pb1−xLax)TiO3 (x = 0–0.05) ceramics were successfully prepared without using a hot-pressing technique. The optical transmittance at the wave length of 400–2000 nm increased with increasing lanthanum (La) content, x from 0 to 0.03. The transmittance at 600–2000 nm further increased (with the highest transmittance of 68% at 2000 nm for ceramics with thickness of 0.5 mm) at x = 0.04 and 0.05, while the transmittance at 400–600 nm decreased. X-ray diffraction patterns suggested that the overall increase in the transmittance with x was associated with a change in the crystal systems from a monoclinic phase to a pseudocubic phase, and the decrease at x = 0.04 and 0.05 was related to the formation of an impurity second phase. Their microstructures and dielectric properties were also studied.

High energy laser (HEL) systems are currently being evaluated for various land, sea, and air based platforms. Some of these systems operate in or have to withstand harsh environment of sand storm, hurricane, and rain. The exit aperture on a HEL system operating in harsh environment can become the single point of failure. Current HEL systems operating in 1–2 µm wavelength use fused silica windows which are at risk of damage in the theater. Rugged window materials such as sapphire, ALON, and spinel are currently being evaluated as a potential replacement. One of the major parameters in window selection apart from its ruggedness is its absorption loss coefficient at laser wavelength. This paper reports on 3 different methods to reduce absorption loss in spinel ceramic from 100,000 ppm/cm down to 75 ppm/cm. The results are compared with ALON and sapphire.

Pure single-crystalline bismuth (III) sulfide (Bi2S3) nanowires with lengths of the long and short axes being 1.58–1.75 μm and 40 nm were prepared by a simple surfactant-assisted reflux method in the presence of thioacetamide, which served as both the sulfur source and a “soft template” in the formation of bismuth sulfide nanostructures. The effects of different surfactant, surfactant molecular weight, solvent medium, and sulfur source on the morphology, structure, and phase composition of the as-prepared Bi2S3 products were discussed. The formation of long Bi2S3 nanowires was probably via the mechanism of pyrolysis of bismuth (III) sulfide complexes dimer and continuous growth of crystalline nuclei along rod-shaped micelles originated from “soft-template” of polyethylene glycol (PEG-800). Besides, ultraviolet–visible spectroscopic (UV-Vis), and photoluminescent (PL) Bi2S3 band features indicated that the nanowires have excellent optical properties, in the optical field of potential applications.

Yttrium aluminum garnet (YAG)-based ceramics represent a valuable alternative to single crystals as active media in laser devices for specific applications. In this connection, the 1.5–1.65 µm emission channel of Er3+-doped YAG is of particular importance for the realization of diode pumped solid state lasers operating in the so-called ‘eye-safe’ region. A well-known drawback of this material is related to its small absorption cross section in correspondence to the diode pumping radiation at 940–980 nm. However, its emission performance can be significantly improved through sensitization with Yb3+ ions that can efficiently absorb the excitation radiation and transfer it to the Er3+ ions. This work deals with the fabrication of polycrystalline YAG co-doped with Er3+ and Yb3+ ions from oxide powders via solid state sintering in high vacuum conditions and its microstructural analysis by transmission electron microscopy–energy-dispersive x-ray spectroscopy to determine the dopants distribution and to assess their influence on the sintering process and on the spectroscopic properties. For this purpose, the absorption and emission spectra of the prepared material have been measured and compared with those of a single crystal having the same composition, appositely prepared by the micro-pulling down method. Suitable calculations have been finally carried out to verify the effective perspectives of application of the investigated ceramics as active lasing medium.

The commercially abundant low purity calcium fluoride powder was directly loaded for spark plasma sintering (SPS). In a vacuum atmosphere with a constant pressure held at 70 MPa the sintering temperature was systematically varied in the range of 500–850 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques were used to characterize the raw powder; and for studying the microstructural properties and in-line transmittance of the finalized ceramics, SEM and Fourier transform infrared spectroscopy (FTIR) were used. Digital images of the 700 °C sintered translucent CaF2 ceramic were taken along with transmittance recordings. The grain growth mechanisms and activation energy values were determined; and the influences of temperature on the relative density, grain size, and optical transmittance were demonstrated. Furthermore, for the first time, a plausible predominant mechanism was proposed for describing the different sintering stages of calcium fluoride ceramics.

The solid-state reaction of yttrium aluminum garnet (YAG, Y3Al5O12) during the heat treatment of Y2O3 and Al2O3 powder mixtures, differing in particle size and size ratio, was quantified using in situ high-temperature x-ray analysis and Rietveld refinement. Y2O3 particle size has the most profound effect on YAG formation. When the Y2O3 particle size was decreased from 5000 to 30 nm (on reaction with 270 nm Al2O3), the YAG formation rate increased from 20 to 48 vol% min−1 over the temperature range of 1350–1450 °C. In this case, the final YAG content increased from 75 to 91 vol%. A simple model that includes the reactant particle coordination number, and thus particle size ratio, shows that when the size ratio (dA/dY) is >1 diffusion through the alumina powder is rate controlling whereas when the ratio is <1, diffusion through the yttria, intermediate phases, and YAG is rate controlling.

Ceramic wafers of alumina (Al2O3) were produced by tape casting of aqueous slurry followed by vacuum sintering. The binder system used to form the tape casting slurry is a copolymer of isobutylene and maleic anhydride, which is environmentally friendly, marketed under the name ISOBAM. The rheological properties of the slurries were studied by varying solid loading and binder addition level. Through the optimization of plasticizer addition, green tapes were casted with excellent plasticity and a thickness of 240–740 μm. The tapes displayed a post-sintering thickness of 150–660 μm. The morphologies, as well as the fracture surface and the as-sintered surface of the powder were examined using a scanning electron microscope (SEM). The in-line transmittance of the transparent unpolished Al2O3 wafers with a thickness of 660 μm was found to be 72% at a wave length of 5 μm and 26% at a wave length of 600 nm.

Translucent, polycrystalline YAG:Ce disks with 0.1, 0.5, and 1 mol% concentrations of cerium as well as different resulting thicknesses of 0.5 and 0.8 mm were prepared by reaction sintering of yttria, alumina, and cerium oxide under vacuum at a temperature of 1800 °C. The obtained samples displayed a microstructure with a Y3Al5O12 main phase interrupted by an intended scattering phase of alumina. Furthermore, the total forward transmittance was between 75 and 78% with the typical absorption bands of cerium at wavelengths of 330 and 460 nm. Phosphor conversion light-emitting diodes (LEDs) with 0.88 W power dissipation have been prepared from these YAG:Ce ceramic disks as converters and blue 455 nm LED chips for excitation. Their color coordinates in the CIE (Commission Internationale de l’Eclairage) diagram determined by spectral photometry depend on the concentration of the Ce dopant and the ceramic converter thickness. The highest luminous flux of 276 lm with an efficiency of 76.6 lm/W was measured for a converter with 0.5 mol% dopant concentration and 0.8 mm thickness emitting a yellowish white light.

The aluminothermic reduction and nitridation method using microsized Al powder and nanosized alumina powder was employed to fabricate AlON powder under N2 atmosphere. Single-phase aluminum oxynitride (AlON) can be prepared at a relatively low temperature (1700 °C) with a holding time of 3 h. The powder is ball milled, doped with different amounts of Y2O3 (0.1–0.9 wt%) as a sintering additive, and then shaped into pellets. The pellet sintering is carried out at two relatively low temperatures (1860 and 1880 °C) for 10 h. The transmittance and hardness of the obtained samples varies as the amount of Y2O3 varies. The sample sintered under optimal conditions can reach an ultimate transmittance of 65% with 2 mm thickness. The Vickers hardness of highly transparent AlON ceramic is about 15.95 ± 0.17 GPa, indicating that our method has a promising future in transparent AlON ceramic production. The sintering promoting mechanisms of Y2O3 are also discussed in detail.

Gadolinium-based transparent polycrystalline ceramic garnet scintillators are being developed for gamma spectroscopy detectors. The scintillator light yield and energy resolution depend on many of the ceramic characteristics, including composition, homogeneity, and presence of secondary phases. To investigate phase stability dependence on composition, three base compositions – Gd3Ga2.2Al2.8O12, Gd1.5Y1.5Ga2.2Al2.8O12, and Gd1.5Y1.5Ga2.5Al2.5O12 were studied, and for each composition the rare earth content was varied according to the formula (Gd,Y,Ce)3(YXGa1−X)2(Ga,Al)3O12; where −0.01 < X < 0.05. We have found that yttrium and gallium help to stabilize the garnet crystal structure in the ceramics by allowing interionic substitution among the cationic garnet sites. Specifically, a composition of Gd1.49Y1.49Ce0.02Ga2.5Al2.5O12 can accommodate approximately 2 at.% excess rare earth ions from the perfect garnet stoichiometry and remain a phase pure transparent ceramic with optimal performance as a radiation detector. This expanded phase stability region helps to enable the fabrication of large transparent ceramics from powder with tolerance for flexibility in chemical stoichiometric precision.

We report the effect of nonstoichiometry on the terahertz absorption of fully dense optical ceramics of Y3Al5O12 and compare to that of undoped and 1 at.% Nd3+ doped single crystals. Our research is motivated primarily by the necessity of having better control of stoichiometry during the preparation of transparent yttrium aluminum garnet (YAG) ceramics. A set of twenty ceramic samples was prepared by solid-state sintering of Y2O3 and Al2O3 powder mixtures with compositions ranging from −0.62 to +0.96 mol% of Y2O3 on each side of the stoichiometric garnet composition. After sintering, the samples were highly translucent in the visible range, with attenuations better than 2 cm−1. These samples were characterized using time-domain terahertz spectroscopy between 0.06 and 2.8 THz. Ceramic and single-crystal samples exhibit a similar broad absorption band, which we assign to a 2-phonon difference process, and whose width and intensity depend upon composition.

Yttrium–aluminum garnet doped with Ce was plasma sprayed using two different processes – gas-stabilized plasma torch and water-stabilized plasma torch. Coatings on various substrate materials (stainless steel, ceramics, YAG undoped crystals), as well as self-standing plates, were obtained. The coatings adhered on materials with relatively large variety of thermal expansion coefficient. Besides microstructural, crystallographic, and thermal-stability investigations, numerous optical tests were performed. They included cathodoluminescence (CL), UV-VIS-NIR reflectance, and response of the Ce:YAG on light with various wave lengths. After spraying, the desired YAG crystalline phase sustained without any decomposition, but an amorphous fraction was present in both types of coatings. Selected coatings were heat-treated to crystallize fully and change their optical properties. Minor amorphous fraction crystallized at 930 °C. The heat-treated coatings exhibited higher CL and also larger visible emission when illuminated with a 366 nm lamp. Microhardness of the coatings was tested as well and proved the mechanical similarity of both coating types and difference from the single crystal. The optical responses of the coatings were influenced by imperfections like splat boundaries, pores, and thin cracks, which were healed only partly by heat treatment. However, the Ce:YAG was first plasma sprayed and moreover produced by both spray techniques without an irreversible loss of the desired garnet phase.