Photoluminescence study of SiO₂ coated Eu³⁺:Y₂O₃ core-shells under high pressure

Uniform core-shell Eu3+:Y2O3/SiO2 spheres were synthesized via precipitation and the Stber method.The structural transition of core-shell Eu3+:Y2O3/SiO2 was studied by using high pressure photoluminescence spectra.With pressure increasing,the emission intensities of 5D0→7F0,1,2 transitions of Eu3+ ions decreased and the transition lines showed a red shift.The relative luminescence intensity ratio of 5D0→7F2 to 5D0→7F1 transitions decreased with increasing pressure,indicating lowering asymmetry around Eu3+ ions.During compression,structural transformation for cores in the present core-shell Eu3+:Y2O3/SiO2 sample from cubic to monoclinic took place at 7.5 GPa,and then the monoclinic structure turned into hexagonal above 15.2 GPa.After the pressure was released,the hexagonal structure transformed back to monoclinic and the monoclinic structure was kept stable to ambient pressure.     

Pressure and temperature dependent up-conversion properties of Yb~(3+)-Er~(3+) co-doped BaBi_4Ti_4O_(15) ferroelectric ceramics

Yb3+ and Er3+ co-doped BaBi4Ti4O15(BBT) ceramic samples showed brighter up-conversion photoluminescence(UC-PL) under excitation of 980 nm. The monotonous increase of fluorescence intensity ratio(FIR) from 525 to 550 nm with temperature showed that this material could be used for temperature sensing with the maximum sensitivity to be 0.0046 K–1 and the energy difference was 700 cm–1. Moreover, the sudden change of red and green emissions around 400 oC might imply a phase transition. With increasing pressure up to 4 GPa, the PL intensity decreased but was still strong enough. These results illustrated the wide applications of BBT in high temperature and high pressure conditions.     

Size dependence of up-conversion luminescence of NaYF₄:Yb³⁺/Tm³⁺

Tm3+/Yb3+ codoped NaYF4 microcrystals were synthesized using a hydrothermal method.The bright upconversion light was observed under 980 nm excitation.The upconversion luminescence was systematically investigated at different Yb3+ concentrations and different reaction temperatures and time.The sample with 60% Yb3+ concentration and reacting at 180 oC for 24 h possessed the highest luminescent efficiency.The higher luminescent efficiency was contributed to a large surface area.The large surface area induced the large vibration mode by absorbed H2O and CO2.The larger vibration mode could enhance the energy transfer efficiency from the excited Yb3+ to Tm3+ by the process of phonon assisted energy transfer.     

RDX、HMX及CL-20晶体的高温高压相变研究进展

环三亚甲基三硝胺(RDX)、环四亚甲基四硝胺(HMX)和六硝基六氮杂异伍兹烷(CL-20)三种多晶型含能材料在高压/高温高压下具有丰富的相变行为及相变特征,本文总结了三种炸药在不同压力环境下的相变路径、部分相结构及p-T相图,为含能材料的爆轰行为和理论研究工作提供参考。根据目前的研究现状,发现在较复杂的相变研究上仍存在分歧,大部分高压相的结构还不明确,p-T相图不够完善,相变理论的研究也存在明显不足。指出探索含能材料的不同晶型间转化机理和获取更多相结构信息将是未来的重点研究方向。