Phenanthroimidazole-Based Organic Fluorophores for Organic Light-Emitting Diodes

Considering the imminent global energy crisis and inefficient energy utilization, energy-efficient organic light-emitting diodes (OLEDs) are considered one of the most competitive candidates for displays and particularly for future energy-saving lighting sources. Full color displays require all primary colors: red, green, and blue (RGB). In recent decades, numerous phenanthroimidazole (PI) RGB-emitting materials have been developed for efficient OLEDs. In organic electronics, considerable interest is shown on PI, due to ease in fluorophore modification. This chapter focuses on the design and synthesis of PI-based materials and their applications in OLEDs. At first, some nondoped blue, green, and yellow fluorescent materials are comprehensively studied. Then attention has been paid for typical blue, green, yellow, orange, and red PhOLEDs of PI-based fluorophores as a host materials are briefly presented. The molecular design concept, general synthetic routes for PI materials, and the applications of fluorophores in fluorescent OLEDs and host materials in PhOLEDs are reviewed.

Photon Upconversion in Lanthanide-Activated Inorganic Luminescent Materials

The growing demand for energy-efficient materials needs advancement in existing approaches. Photon upconversion is an effective way to overcome this issue. Novel upconverting materials show their potential in the advancement of energy conservation and lighting technology. In this contest, lanthanide-activated inorganic luminescent materials play a key role. The unique features of these materials like non-toxic nature, narrow multicolour emissions, long luminescence lifetime, high signal/noise ratio, and good chemical durability make them more promising. In this chapter, an overview of photon upconversion process in various lanthanide doped/codoped materials is given. Introductory idea about upconversion mechanism, criteria of material selection, novel synthesis roots, reports on upconversion-emitting materials, and emergent applications of these materials are presented.

An Overview on Peak Shape Method for Thermoluminescence Glow Curve Analysis

The shape of a thermoluminescence (TL) glow curve has fundamental importance for calculating the characteristic parameters of trap levels within the band gap. TL analysis are mostly based on the three-parameter general order kinetics model. The parameters are activation energy, order of kinetics, and frequency factor. Peak shape method is one of the most prominent methods for extracting the activation energy from a TL curve. An overview of different peak shape methods along with an alternative approach formulated directly from basic TL equations is presented in this chapter. Generally, peak shape method requires prior knowledge of order of kinetics to determine activation energy which creates a difficulty due to the non-uniqueness of symmetry factor for a particular value of order of kinetics. A modified version of peak shape method which is free from this constraint is discussed here. Activation energies from experimental curves of tremolite and actinolite are estimated using peak shape method. Limitation of peak shape method for saturated TL peaks with heavy retrapping is also discussed.

Thermo, Photo and Mechanoluminescence Studies of Eu3+ Doped Y4Al2O9 Phosphors

The chapter reports synthesis and characterization of europium-doped Y4Al2O9 phosphor for display and dosimetric applications. The europium-activated Y4Al2O9 (YAM) phosphor is synthesized via solid state reaction method. Synthesized phosphors were characterized by powder x-ray diffraction (PXRD) techniques, scanning electron microscopy (SEM) technique, and transmission electron microscopy (TEM) technique. Particle size calculated from TEM analysis and crystallite size was calculated by Scherer's formula. All synthesized phosphor for different concentration of europium ion were studied by photo, thermo, and mechanoluminescence study. It is found that for photoluminescence analysis of Eu3+ doped phosphor has prominent spectra in red region and electric dipole transition (5D0 → 7F2) dominant over the magnetic dipole transition (5D0 → 7F1) due to non-centro symmetry between rare earth ions. Broad excitation spectra found for photoluminescence study.

Phosphors for Various Dosimetry Applications Derived by Different Synthesis Routes

The chapter provides useful information about synthesis and characterization of dysprosium doped oxide and fluoride-based phosphors such as SrGd2O4, CaSO4, and CaF2. Various techniques (e.g., acid-recrystallization, chemical co-precipitation, and homogenous precipitation cum auto-combustion methods) were adopted to synthesize these phosphors for large-scale production. All the prepared phosphors were characterized by x-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy techniques. The thermoluminescence (TL) studies were performed after different irradiation sources such as gamma rays, thermal neutrons, and low energy ions (H, Ar, and N), respectively. Linear dose responses were observed in a wide range of doses for all the samples. Various trapping parameters, namely order of kinetics, activation energy, and frequency factors, were calculated by using computerized glow curve deconvolution (CGCD) method.

Electroluminescence Principle and Novel Electroluminescent Materials

Over the past few decades, many efforts have been put to optimize the properties of electroluminescent devices such as electroluminescence (EL) panel, organic light emitting diode (OLED), flat panel display, EL lamps, etc. In this chapter, the authors provide a comprehensive review of the state-of-the-art research activities related to EL phenomena, the principle of electroluminescence, different types of EL, fabrication of devices, studies on novel electroluminescent materials, their characteristics and potential applications. The authors begin with a historical background of electroluminescence, description of its structure, working principle and parameters with mechanism. They discuss the experiments determining the electrical, optical, and physical properties of the powder as well as thin film EL cells. The recent progress on the improvement of their characteristics and finding novel structures, such as the latest achievements in using various semiconductor nanostructures in polymer matrix as emitting layer in EL devices, are summarized.

White Light Emitting Phosphors for Solid State Lighting

Phosphor materials are an integral and important part in the white light generation in LEDs and have participated in the global warming reduction significantly. In this chapter, the authors focus on different types of phosphor materials belonging to a family of apatites, fluoroapatites, silicates, oxides, phosphates, and borates with different crystal structures. The detailed investigations on their crystal chemical structure, synthesis, and photoluminescence properties are briefly discussed. The improved optical properties make the phosphor potential candidate for smart panel displays and white light emitting diodes (including solid state lighting). The crystal structure has a great influence on the chemical and luminescence properties of any phosphor; hence, a great change of activator ion (Eu2+, Ce3+, Mn2+, and Tb3+) concentrations can be achieved in the phosphor performances. The chapter correlates the structure-compositions-property of the phosphor materials with special emphasis on white LEDs.

Upconversion Luminescence Behaviour of Er3+/Yb3+ Doped MY2O4 (M=Ba, Ca, Sr) Phosphors

The upconversion (UC) of the rare earth doped MY2O4 (M=Ba, Sr, Ca) has been extensively investigated due to their potential applications in many fields, such as color display, high density memories, optical data storage, sensor and energy solar cell, etc. Many series of them, especially the Er3+, Yb3+ doped MY2O4 were studied in this chapter, due to the thermal and mechanical toughness, high optical transmittance from the ultraviolet to the infrared regions, and a low nonlinear refractive index compared to the other commercial laser glasses. The energy transfer (ET) mechanism of rare earth doped phosphor plays an important role in the upconversion process.

Swift Heavy Ion Synthesis and Modifications of Nanophosphors for Dosimetric Application

Recently, there has been a huge demand for the experimental and theoretical efforts for the dosimetry of the ionizing radiation due to its diagnostic and therapeutic purposes. Different ionizing radiations include low ionizing radiation such as x-rays, γ-rays and densely ionizing radiation swift heavy ions (SHIs). When SHIs pass through a material, intense electronic excitations occur along the ion trajectory due to the inhomogeneous distribution of the energy inside the material. This internal disorder creates a large number of defects in the materials. The characterization of such defects provides material's technological importance for different practical applications in radiation dosimetry. Different luminescence behavior including thermoluminescence (TL) is the well-established and very sensitive technique for the characterization of the structural disorder and defects in solids. Therefore, this chapter deals with the basic concept of swift heavy ion and ion-induced modification for dosimetric applications.

Perspectives of Hydrothermal Synthesis of Fluorides for Luminescence Applications

Hydrothermal synthesis is an easy, portable, less-hazardous, and low-cost synthesis method. Various researchers across the globe are worked on the synthesis of different materials via this route. Practically, fluorides are difficult to synthesize due to their hygroscopic nature by conventional methods. But, the hydrothermal synthesis is used to prepare several compositionally optimized fluoride-based materials using closed-system physical and chemical processes in an aqueous solution at low temperatures and pressures. The silent features of the hydrothermal method over conventional methods of materials processing are a crystallization of materials, crystal growth, in the processing of a wide range of materials not only the bulk crystals but fine particles with a controlled size and morphology. Therefore, in order to place its numerous recent developments, past and current research come together in this chapter. This chapter is a recent clocking update for synthesis, materials, and their applications.