A translucent Gd2O2S:Pr ceramic scintillator with an in-line transmittance of ~31% at 512 nm was successfully fabricated by argon-controlled sintering. The starting precipitation precursor was obtained by a chemical precipitation route at 80 °C using ammonia solution as the precipitate, followed by reduction at 1000 °C under flowing hydrogen to produce a sphere-like Gd2O2S:Pr powder with an average particle size of ~95 nm. The Gd2O2S:Pr phosphor particle exhibits the characteristic green emission from 3P0,1→3H4 transitions of Pr3+ at 512 nm upon UV excitation into a broad excitation band at 285–335 nm arising from 4f2→4f5d transition of Pr3+. Increasing Pr3+ concentrations induce two redshifts for the two band centers of 4f2→4f5d transition and lattice absorption on photoluminescence excitation spectra. The optimum concentration of Pr3+ is 0.5 at.%, and the luminescence quenching type is dominated by exchange interaction. The X-ray excited luminescence spectrum of the Gd2O2S:Pr ceramic is similar to the photoluminescence behavior of its particle. The phosphor powder and the ceramic scintillator have similar lifetimes of 2.93–2.99 μs, while the bulk material has rather higher external quantum efficiency (~37.8%) than the powder form (~27.2%).
The work presents electrical properties of Nd–PMN–PT single crystal grown by Bridgman method. As-grown crystal has been verified to have ultrahigh piezoelectric coefficient d33 with maximum value of 3650 pC N−1 under alternating current polarization.
Using LiF and YF3 as starting materials, we prepare feed material from fluorides according to the molar ratio of LiF:YF3 = 51.5:48.5. The anhydrous LiYF4 polycrystalline material is synthesized via the fluoridation process with a dried HF flow at elevated temperature. By charging the feed material and adding a small amount of active carbon powder in a sealed platinum crucible, the crystal can be grown via the vertical Bridgman method in a nonvacuum atmosphere. This is possible because the oxidization and volatilization of the melt is avoided. Using optimum conditions, that is, a growth rate of 0.5–0.6 mm/h and a temperature gradient of 25–30 oC/cm across the solid-liquid interface under a furnace temperature of 920–930 oC, the colorless crystal LiYF4 with the size of \phi 25 \times 50 (mm) is successfully grown. The optical transmittance of the crystal is as high as 85% above the absorption edge at 190 nm. The induced absorption bands are observed below 700 nm in the transmission spectrum after the crystal is subjected to a high dose of \gamma-ray irradiation.
1 March 2019 in Inorganic Chemistry Communications