Entwicklung neuer Leuchtstoffe für die Hochtemperatur-Thermometrie

The temperature is one of the most important parameters for the analysis, evaluation, and optimization of numerous technical applications in chemistry, biomedicine, process and power engineering. Therefore, the improvement of existing and development of new techniques in thermometry is of crucial importance. The phosphor thermometry as a relatively new technique based on the laser-induced luminescence offers the possibility of non-contact temperature measurement extensively and promptly with high sensitivity and accuracy. The phosphor thermometry utilizes temperature-dependent luminescence characteristics of an optically active dopant ion embedded in a crystalline host lattice. The development of new phosphor materials is an important task to be solved for each specific application, such as temperature measurements on surfaces or in gaseous flows. The focus of this work was to expand the range of thermographic phosphors for high-temperature measurements and the improvement of the specific parameters as high luminescence intensity, high sensitivity, a long or short lifetime of the luminescence. The thesis is structured in the following way which reveals the systematic development of such phosphors. Chapter 1 provides an in-depth introduction into the historical development of thermometry and a brief introduction to the basic theory involved in thermometry mechanisms. The most important competing techniques for temperature measurements with their advantages and disadvantages in comparison with phosphor thermometry are discussed. Then the factors which are influencing the photoluminescence behavior of the thermographic phosphors are presented. After the introduction part Chapter 2 describes the materials and methods used for the synthesis and investigation of the thermographic phosphors. The following four Chapters describe the investigation of phosphor material namely yttrium aluminum garnet Y3Al5O12:Dy, Y3Al5O12:Dy, Er with addition of boron nitride (BN) (Chapter 3), Y3Al5O12:Dy and its mixture with yttrium aluminum perovskite YAlO3 (Chapter 4), yttrium orthosilicate Y2SiO5:Dy (Chapter 5), and calcium scandium silicate garnet Ca3Sc2Si3O12:Dy, Ce (Chapter 6). Each Chapter consists of a brief overview of state of the art regarding specific composition, structural and morphological study what follows by photoluminescence investigations. Many of the aspects influencing the photoluminescence properties such as synthesis methods or auxiliary compounds are investigated in order to optimize photoluminescence properties of materials under study. Finally, the thermal response of the investigated phosphors, determining the working temperature range by the intensity ratio method or decay time characteristics, are highlighted. Die Temperatur ist einer der wichtigsten Parameter für die Analyse, Bewertung und Optimierung zahlreicher technischer Anwendungen in Chemie, Biomedizin, Prozess- und Energietechnik. Daher ist die Verbesserung bestehender und die Entwicklung neuer Techniken in der Thermometrie von entscheidender Bedeutung. Die Phosphorthermometrie als eine relativ neue Technik basierend auf der laserinduzierten Lumineszenz bietet die Möglichkeit von schnellen und berührungslosen Temperaturmessungen mit hoher Empfindlichkeit und Genauigkeit. Die Phosphorthermometrie verwendet temperaturabhängige Lumineszenzeigenschaften eines optisch aktiven Dotierstoffions, das in einem kristallinen Wirtsgitter eingebettet ist. Die Entwicklung neuer Leuchtstoffmaterialien ist eine wichtige Aufgabe, die für jede spezifische Anwendung gelöst werden muss, z. B. Temperaturmessungen an Oberflächen oder in gasförmigen Strömen. Der Schwerpunkt dieser Arbeit lag auf der Erweiterung der Palette der thermographischen Leuchtstoffe für die Hochtemperaturmessung und auf der Verbesserung spezifischer Parameter, wie hohe Lumineszenzintensität, hohe Empfindlichkeit, lange oder kurze Lebensdauer der Lumineszenz. Im Folgenden wird der Aufbau der Arbeit beschrieben, der die systematische Entwicklung der Leuchtstoffe wiederspiegelt. Das Kapitel 1 gibt eine ausführliche Einführung in die historische Entwicklung der Thermometrie sowie eine kurze Einführung in deren grundlegende Theorie. Die wichtigsten konkurrierenden Techniken für Temperaturmessungen mit ihren Vor- und Nachteilen werden mit der Phosphorthermometrie verglichen. Danach werden die Faktoren, die das Photolumineszenzverhalten der thermographischen Leuchtstoffe beeinflussen, vorgestellt. Nach dem Einführungsteil beschreibt Kapitel 2 die Materialien und Methoden, die für die Synthese und Untersuchung der thermographischen Leuchtstoffe verwendet werden. Die nachfolgenden vier Kapitel befassen sich mit der Untersuchung von Phosphormaterialien: Yttrium-Aluminium-Granat Y3Al5O12:Dy, Y3Al5O12:Dy, Er mit Zugabe von Bornitrid (BN) (Kapitel 3), Y3Al5O12:Dy und einer Mischung von Yttrium-Aluminium-Perowskit YAlO3 (Kapitel 4), Yttriumorthosilikat Y2SiO5:Dy (Kapitel 5) und Calcium Scandium Silikat Granat Ca3Sc2Si3O12:Dy, Ce (Kapitel 6). Jedes Kapitel besteht aus einem kurzen Überblick über den Stand der Technik bezüglich spezifischer Zusammensetzung, struktureller und morphologischer Studien, die aus Photolumineszenzuntersuchungen folgen. Viele der Aspekte, die die Photolumineszenzeigenschaften beeinflussen, wie Syntheseverfahren oder Hilfsverbindungen, werden untersucht, um die Photolumineszenzeigenschaften der untersuchten Materialien zu optimieren. Abschließend wird die thermische Antwort von den untersuchten Leuchtstoffen, die den Arbeitstemperaturbereich durch das Intensitätsverhältnisverfahren oder die Abklingzeitcharakteristik bestimmen, hervorgehoben

Eu3+ Sensitization via Nonradiative Interparticle Energy Transfer Using Inorganic Nanoparticles

Phosphors have been used successfully for both research and commercial applications for decades. Eu3+-doped materials are especially promising, because of their extremely stable, efficient, and narrow red emission lines. Although these emission properties are ideal for lighting applications, weak absorption in the blue spectral range has until now prevented the use of Eu3+-based phosphors in applications based on blue light-emitting diodes. Here, we demonstrate a sensitization mechanism of Eu3+ based on interparticle Förster resonance energy transfer (IFRET) between lanthanide-doped inorganic nanocrystals (NCs). Compared to co-doping different lanthanides in the same host crystal, IFRET allows an independent choice of host lattices for Eu3+ and its sensitizer while potentially greatly reducing metal-to-metal charge transfer quenching. We demonstrate IFRET between NCs, resulting in red Eu3+ emission upon blue excitation at 485 nm using LaPO4:Tb/LaPO4:Eu and LaPO4:Tb/YVPO4:Eu NC mixtures. These findings pave the way toward engineering blue-sensitized line emitters for solid-state lighting applications

Melamine-functionalized graphene oxide: Synthesis, characterization and considering as pseudocapacitor electrode material with intermixed POAP polymer

In this study, Melamine functionalized graphene oxide (FGO-Melamine) was synthesized by chemical route. The prepared functionalized graphene oxide was characterized by different analytical techniques such as FT-IR, Raman spectroscopy, thermogravimetry coupled with mass spectrometry (TG-MS), X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS). To improve electrochemical properties of polyorthoaminophenol (POAP), the electropolymerized POAP/FGO-Melamine films, employed as an active electrode regarding electrochemical performance. In terms of electrochemical measurements, galvanostatic charge–discharge evaluation, EIS (electrochemical impedance spectroscopy) and CV (cyclic voltammetry) were employed for conducting an enquiry into supercapacitive performance of nanocomposite of POAP/FGO-Melamine. This graphene-based electrode showed a specific capacitance (SC) by 273 F g−1 and high energy of 37.91 W kg−1 at power density of 500 W kg−1. The novel materials synthesized in the current work show higher efficiency compared to the carbon-based ones concerning redox reactions of capacitors consisting of good stability in the existence of aqueous electrolyte, large active surface area and ease synthesis method. © 2018 Elsevier B.V

Eu3+ Sensitization via Nonradiative Interparticle Energy Transfer Using Inorganic Nanoparticles

Phosphors have been used successfully for both research and commercial applications for decades. Eu3+-doped materials are especially promising, because of their extremely stable, efficient, and narrow red emission lines. Although these emission properties are ideal for lighting applications, weak absorption in the blue spectral range has until now prevented the use of Eu3+-based phosphors in applications based on blue light-emitting diodes. Here, we demonstrate a sensitization mechanism of Eu3+ based on interparticle Förster resonance energy transfer (IFRET) between lanthanide-doped inorganic nanocrystals (NCs). Compared to co-doping different lanthanides in the same host crystal, IFRET allows an independent choice of host lattices for Eu3+ and its sensitizer while potentially greatly reducing metal-to-metal charge transfer quenching. We demonstrate IFRET between NCs, resulting in red Eu3+ emission upon blue excitation at 485 nm using LaPO4:Tb/LaPO4:Eu and LaPO4:Tb/YVPO4:Eu NC mixtures. These findings pave the way toward engineering blue-sensitized line emitters for solid-state lighting applications