Tuning of emission by effect of local symmetry in BaLaLiWO6:Dy3+/Eu3+ for WLEDs

The luminescence center energy transfer, crystal field strength, and covalency are limited by the crystal structure of the host and subsequently affect the luminescence efficiency, color, and intensity. Here, we report an excellent red phosphor BaLaLiWO₆:0.40Eu³⁺ and the dependence between symmetry and luminous performance. A model for changing symmetry is drawn by analyzing the Coulomb potential and structure for the application of a double-perovskite phosphor BLLWO: Dy³⁺, Eu³⁺ in white light LEDs. The addition of Dy³⁺/Eu³⁺ makes the W-O bond formed by the B-site and oxygen ion longer and the Li-O bond shorter, and the difference between the eight octahedral around the A-site is reduced, increasing the symmetry of the A-site. Local symmetry was successfully modulated by changing the Eu³⁺ concentration to control the Y/B ratio of Dy³⁺ and the R/O ratio of Eu³⁺ and smoothly achieved (0.382, 0.373) warm white light color coordinate. The phosphor has excellent thermal stability and still has 92.3% intensity at 475 K. The above results show that the wavelength composition of the luminescence is tunable by changing the symmetry of the environment in which the doped ions are located. It applies to single hosts for the regulation of white light emission.     

Hydroxylation mechanism of phase regulation of nanocrystal BaTiO3 synthesized by a hydrothermal method

Understanding the phase regulation mechanism of BaTiO₃ synthesized by a hydrothermal method is a complicated and challenging task. Here, we successfully prepared cubic and tetragonal BaTiO₃ single nanocrystals by changing the ratio of water and ethanol in the solvent. We confirm that the BaTiO₃ phase is mainly affected by the hydroxylation process due to the reaction with solvent. In particular, ethanol can be catalytically oxidized by titanium atoms, cause BaTiO₃ hydroxylation and promote the formation of a cubic phase. In the mixed solution of ethanol and water, the hydroxylation process is suppressed, which facilitates the formation of the tetragonal phase. The relationship framework between the solvent ratio, phase structure and hydroxyl defects of BaTiO₃ is established. Tetragonal BaTiO₃ with fewer hydroxyl defects can promote charge transfer and surface reaction after polarization, thereby enhancing their photoelectric catalytic performance. This work provides references for the controllable synthesis of ferroelectric nanocrystals by hydrothermal methods and new insight for the utilization of polarization in photoelectrocatalysis applications.     

Better safe than sorry? Stated preferences and the precautionary principle for securing drinking water quality in an Italian district

We apply Contingent Valuation (CV) to investigate individuals’ preferences concerning an alleged contaminant – asbestos contained in fibrolite pipes – which, although not identified so far as a major threat to drinking water, is raising public concern. In the district of Gorizia in Northern Italy, though contrary to the recommendations of experts, mean WTP is high enough to justify an accelerated replacement of pipes as a precautionary measure. However, interviews reveal a strong polarization, and still provide inconclusive recommendations for policy. Our analysis contributes to the debate on the applicability of stated-preference techniques to choices concerning the precautionary principle when highly emotional topics are under discussion.     

中国煤层气产业对外合作政策研究

中国拥有丰富的煤层气资源，与天然气相比，煤层气的开采具有单井产量低、投资回收期长等特点。目前，中国还缺乏成熟的煤层气开发技术，需要引进外资及先进的技术和管理经验。本文通过分析国外特别是美国政府对煤层气产业的扶持政策及其成功经验，对比了中国现行的产业政策，提出了加快中国煤层气产业对外合作发展的政策建议。     

提高风机系统节能改造的途径

风机在全国数量众多,分布面广,耗电量巨大,因此风机节能具有巨大的经济意义,风机的节能改造包括风机的更新与改造两方面,介绍了更新的方式和改造的几个方面,指出变速调节方式是一种高效的调节方式,节能效果相对最好。     

电磁调速采煤机控制系统MATLAB仿真

用最新的计算机仿真工具MATLAB及其Simulink工具箱分析采煤机电磁调速控制系统的动态性能及其抗扰动性能 ,仿真结果表明 :电磁调速控制系统在采煤机上运用性能良好。MATLAB的Simulink工具箱仿真指导设计、调试简单方便而高效 ,仿真结果准确可靠     

BPXH—8变频行星叶轮卸灰机的研制

BPXH－8变频行星叶轮卸灰机采用上下两个灰仓及组叶轮，解决了灰粉自流及卡堵现象；通过延长灰仓的密封长度，防止了灰粉结块。主轴及轴承选用20Cr钢，并进行特殊处理，过流体选用耐磨材料CoMnNb钢，提高了耐磨性，延长了寿命。实践表明，该机是火力发电厂一种新型的优质卸灰机。     

我国西部地质环境保护中的问题与对策

我国西部地质环境的基本特征及存在的主要问题。提出西部地质环境保护的主要对策 ;立法和建立四级地法环境监测体系 ,增加投入、部门关系和落实规划措施 ;开展区域性环境地质调查 ;加强地质环境有关的数据集成及科研与地质灾害的综合整治     

变流量空调水系统的二通调节阀特性分析与选用

本文主要分析了二通阀在变流量系统实际使用过程中流量特性规律以及影响流量特性的因素,并针对系统设计给出了二通阀在系统中阀权度的取值范围。