Optical studies of rare-earth crystal-field excitations in manganites and laser materials/Études optiques du champ cristallin dans les manganites et matériaux laser

光散射、光致发光和红外干涉等光学技术对于发展基础科学和解释固体中的微观相互作用是有用的。我们使用这些技术来更好地了解下列重要的最新高科技材料的基本物理性质： A)-各种多铁化合物(稀土锰酸盐和钒酸盐)，其中磁性和铁电性共存，具有明显的相互作用，这导致了最重要的应用。在这些材料中，电极化由磁场驱动，磁化由电场触发。它们具有巨大的应用潜力，例如导致八态新型存储器件、铁电场效应晶体管和电场控制的磁性元件。 B)-形成稀土离子对相互作用的固体激光器(例如，掺Yb的NdVO4中的Yb-Yb离子)。这种对是光开关和光存储器的本征双稳态的起源。它们也是合作发射的来源，使孤立的Yb离子在绿蓝光下的红外发射翻了一番。 在我们研究的材料中，稀土离子(Pr，Nd，Sm…)是一家公司。我们从四个国际公认的组织获得样品，以了解其晶体生长专业知识的质量。光散射和红外光谱是我们用来探测4f稀土电子的离子振动(声子)、磁激发(磁子)和能级的工具。这些激发和能级构成了探测各种电和磁相互作用(电子-电子、电子-离子和离子-离子)的局部探针。然后，我们使用量子力学的形式，对我们调整和修改的相互作用进行建模，这些相互作用是温度、掺杂以及外加磁场和电场的函数。我们的目标是对这些战略性材料的性质有一个基本的理解，以便指导晶体种植者开发新的战略性化合物，以增强稀土基多铁性材料和激光材料的基本特性，用于新的高科技开发。

Optical techniques such as light scattering, photoluminescence and infrared interferometry are useful to develop fundamental science and to explain microsopic interactions in solids. We use these techniques to better understand the fundamental physical properties of the following important recent high tech materials : a)- various multiferoics (rare-earth manganites and vanadates) in which magnetism and ferroelectricity, that have led to most important applications, coexist with a pronounced interplay. In these materials an electric polarization is actuated by a magnetic field and a magnetization is triggered by an electric field. They are of great application potential leading for instance to eight-state new memory devices, ferroelectric field-effect transistors and electric field controlled magnetic components. b)- solid state lasers in which interacting rare-earth ion pairs are formed (e.g. Yb-Yb ions in Yb doped NdVO4). Such pairs are at the origin of intrinsic bistability for optical switches and optical memories. They are also a source of cooperative emission doubling the infrared emission of the isolated Yb ion in green-blue light. In our studied materials, rare earth ions (Pr, Nd, Sm...) are incorporated. We get samples from four internationally recognized groups for the quality of their crystal growing expertise. Light scattering and infrared spectroscopy constitute our tools to detect the ionic vibrations (phonons), the magnetic excitations (magnons) and the energy levels of the 4f rare-earth electrons. These excitations and levels constitute local probe to detect the various electrical and magnetic interactions (electron-electron, electron-ion and ion-ion). Using quantum mechanics formalism, we then model the interactions that we tune and modify as a function of temperature, doping and applied magnetic and electric fields. We aim to develop a basic comprehension of these strategic materials properties in order to orient the crystal growers in generating new strategic compounds that would enhance the essential particularities of the rare-earth based multiferroics and laser materials for new high tech developments.