Pande Zhang

Europium doped transparent glass ceramics containing CaF2 micron-sized crystals: structural and optical characterization

Transparent glass ceramics containing CaF2 micron-sized crystals were prepared using a modified liquid-phase sintering route. The morphology and microstructural evolution of the CaF2 crystals before and after liquid-phase sintering were examined using X-ray diffraction, field-emission scanning electron microscopy and transmission microscopy. After sintering at 800 °C for 10 min, the CaF2 crystals were approximately 20 μm in size and were uniformly distributed throughout a precursor glass prepared using melt-quenching method. The glass ceramic containing CaF2 micron-sized crystals prepared using liquid-phase sintering achieved the highest in-line transmittance of 76% in the visible region and 92% in the near-IR region. High near-IR transmittance of glass ceramics was attributed to the matching of the refractive index of the precursor glass with that of CaF2 in the near-IR region. The luminescence properties and local environment of Eu3+ in the precursor glass and glass ceramic were investigated using photoluminescence spectra, photoluminescence lifetimes and phonon sideband spectroscopy, and the results determined that some of the Eu3+ ions in the precursor glass incorporate into CaF2 micron-sized crystals after sintering and enter C4v site symmetry.

Effects of annealing on Cr-sensitized Nd:LuAG laser ceramics

This paper demonstrates that annealing can greatly improve the quality of Cr-sensitized Nd:LuAG (Cr,Nd:LuAG) ceramics. Additionally, the pumping efficiency of Nd:LuAG ceramics can be improved by co-doping with Cr3+ ions. The two broad and strong absorption bands around 600 nm (4A2- 4T2) and 440 nm (4A2- 4T1) caused by Cr3+ ions act as effective sensitizers to absorb and convert UV and visible light from a flash lamp. Furthermore, a near-infrared absorption band appears in the in-line transmittance spectra of Cr,Nd:LuAG ceramics. The XPS spectra show that this band is caused by Cr2+ ions. The effect of annealing is studied, and it is found that the near-infrared absorption could be eliminated by annealing in air at 1450 °C for 25 h. Furthermore, the effective fluorescence lifetime of Nd3+ ions in Cr co-doped LuAG ceramics increases from 211.28 μs to 553.80 μs when pumped at 440 nm.

Preparation of LuAG Powders with Single Phase and Good Dispersion for Transparent Ceramics Using Co-Precipitation Method

The synthesis of pure and well dispersed lutetium aluminum garnet (LuAG) powder is crucial and important for the preparation of LuAG transparent ceramics. In this paper, high purity and well dispersed LuAG powders have been synthesized via co-precipitation method with lutetium nitrate and aluminum nitrate as raw materials. Ammonium hydrogen carbonate (AHC) was used as the precipitant. The influence of aging time, pH value, and dripping speed on the prepared LuAG powders were investigated. It showed that long aging duration (>15 h) with high terminal pH value (>7.80) resulted in segregation of rhombus Lu precipitate and Al precipitate. By decreasing the initial pH value or accelerating the dripping speed, rhombus Lu precipitate was eliminated and pure LuAG nano powders were synthesized. High quality LuAG transparent ceramics with transmission >75% at 1064 nm were fabricated using these well dispersed nano LuAG powders.

Nano liquid metal for the preparation of a thermally conductive and electrically insulating material with high stability

Dielectric materials typically demonstrate poor thermal conductivity, which limits their application in emerging technologies in integrated circuits, computer chips, light-emitting diode lamps, and other electronic packaging areas. Using liquid metal microdroplets as inclusions to develop thermal interface materials has been shown to effectively improve thermal pathways, but this type of material may become electroconductive with the application of a concentrated compressive stress. In this study, an isotropic nano-liquid metal thermally-conductive and electrically-insulating material (nLM-THEM) is developed by combining a modified polymer and well-dispersed nanoparticles, achieving an ∼50× increase in thermal conductivity over the base polymer. In addition, the thermal conductivity of nLM-THEMs exhibits no significant change with varying humidity and a stable anti-corrosion effect even in direct contact with aluminum. More importantly, nLM-THEMs demonstrate a stable electrical insulating property upon compressive stress, while conventional micro-LM-THEMs exude liquid metal. This exceptional combination of thermal and electrical insulation properties is enabled by the interconnection of uniform and spherical liquid metal nanoparticles to create more thermally-conductive pathways, and surfactant modified nanoparticles ensure excellent electric insulation. Moreover, this material can achieve passive heat exchange through rapid heat dissipation, which demonstrates its great application potential in the electronic packaging area.

Influence of dopant concentration on the transparent and thermal properties of Nd 2 O 3 -doped alumina translucent ceramics

Abstract The transparent and thermal developments of high-purity Al 2 O 3 doped with different levels of Nd 2 O 3 were investigated. Dopant levels ranged from 500–1500 ppm (Nd/Al atomic ratio). The samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, transmittance spectroscopy and specific heat measurement. Results revealed that with proper Nd doped, Nd 3+ ions solid dissolved in Al 2 O 3 lattice, resulting in small and uniform grain and high bonding vibration, which was beneficial to transparent and thermal properties. With 1000 ppm Nd doped, Al 2 O 3 translucent ceramics showed a total transmittance of 89% and thermal conductivity of 41.7 W/m/K, indicating a potential application as substrate for effective heat dissipation and multi emitting surface in LEDs module.

Re-clustering of neodymium ions in neodymium, buffer ion-codoped alkaline-earth fluoride transparent ceramics

We systematically present the relationship between the optical properties and deformation of Nd,B-codoped MF2 (B = buffer ions; M = alkaline earth metal ions) transparent ceramics. Re-clustering of Nd3+ ions in ceramics was experimentally observed for the first time. The mechanism of re-clustering was studied.