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MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY ----------------------------GRADUATED UNIVERSITY SCIENCE AND TECHNOLOGY DUONG THI GIANG RESEARCH AND DEVELOPMENT OF MICRO-NANO OPTICAL MATERIALS AND FREE-FORM OPTICS USING IN SOLID STATE LIGHTING Major: Optical, optoelectronic and photonic materials Code: 9440127 SUMMARY OF DOCTORAL THESIS IN MATERIAL SCIENCE Ha Noi – 2020 The thesis has been completed at: Graduated University of Science and Technology – Vietnam Academy of Science and Technology Science supervisors: 1. Ass. Prof. Tran Quoc Tien 2: Ass. Prof. Pham Hong Duong Reviewer 1: … Reviewer 2: … Reviewer 3: …. This thesis was defended at Evaluation Council held at Graduated University of Science and Technology – Vietnam Academy of Science and Technology on , 2020 The thesis can be further referred at: - The library of Graduated University of Science and Techonology - National library of Viet Nam 1 INTRODUCTION 1. The necessity of the thesis The process of urbanization is fast, people live and work mainly indoors under artificial lighting. The artificial lighting environment is different from natural light in terms of length, spectral structure, day and night cycle, and the circadian rhythm of residents will be reversed and cause a lot of physical health consequences, physiology and psychology such as insomnia, obesity, poor physiology, infertility, fatigue, even cancer. Therefore, creating a lighting environment for humans to protect eyevision and health is essential. In this thesis, I will systematically present problems to be solved in the field of interior lighting, derived from the knowledge about the role of light for people. Next is the design, manufacture and application of solid lighting products on the basis of LED combined with free-form optical components in interior lighting. 2. The research objectives of the thesis Improve the usability and quality of LED-based lighting products. Develop a new generation of high-efficiency LED lights, evenly distributed, eliminating light pollution, and replacing existing LEDs. 3. The main research content Design and fabricate white LEDs with Remote-phosphor configuration. Calculate, design, simulate and fabricate free-form optical components (FO) for used in solid lighting. Design and fabricate SkyLED luminaires with integrated FO lenses and build some realistic lighting models. 2 CHAPTER I. INTRODUCTION 1.1. Solid state lighting and LED light sources Solid state lighting with a focus on LED light sources has opened up a revolution in lighting where key contributors were awarded the 2014 Nobel Prize in Physics, and in 2015 declared by the International Union is the light year. With outstanding advantages such as energy saving, high efficiency, ability to change the structure of the emission spectrum, safety for the environment and users, LED light source has become the main alternative light sources replacing all other traditional light sources. 1.1.1. Working principle of LED LED - Light-Emitting Diode. To create luminescent devices, straight band gap semiconductors are used with two impurity types donor (n type) and acceptor (p type), creating a zone called p-n junction, while the device is called the diode. In order to increase the quantum efficiency of components, instead of using homogeneous semiconductors, people use semiconductor materials with different band gap Eg to create a p-n junction called a heterogeneous junction. When the p-n junction uses a semiconductor material with a lower Eg sandwiched between two materials with a higher Eg, the free carriers will be locked inside a region with low Eg, called a quantum well. The quantum well structure increases the recombination probability of the carrier, which increases the luminescent efficiency of the component [3]. 1.1.2. Phosphor materials Phosphor-converted materials are very important components that directly affect the quality and efficiency of the LED light source. 3 Commercial luminescent materials currently used for white LEDs include: Garnet, Alluminat, Silicate and Nitride. The challenge for material scientists and manufacturers is to reduce the emission spectral width of these phosphors or to find new materials to replace. 1.1.3. White LED packages (WLED) There are 3 way to fabricate WLED: 1) Using 4 types of LED chips Blue - Amber - Green - Red combined together to form a White LED Module ( RGBA-WLED); 2) UV LED chip combined with Blue Green Red 3-color phosphor; 3) BLED chip combined with 560nm yellow phosphor. The phosphor-converted White LED (Pc-WLED) is the configuration that plays a key role in today's LED packaging market with the advantages: simplicity, high temperature resistance and stable color quality. 1.1.4. LED luminaire An LED luminaire (LED luminaire) used in general lighting is composed of four components, which are the LED module, the driver source, the heat sink, and the optics. 1.1.5. The characteristics of LED light suorces Characteristics that evaluate the quality and effectiveness of light sources are described by the following parameters: optical parameters (luminous flux, power, optical efficiency), color parameters (emission spectrum, color temperature correlation, color rendering coefficient, color cleanliness), luminous intensity and luminous intensity distribution. 1.2. Free-form optical Devices 1.2.1. Free-form optical devices 4 FO optics is the next generation of modern optics, offering outstanding differentiation features and high system integration. FO is defined as the optics of asymmetrical surfaces or of any shape, designed with non-traditional technologies, including: rotating symmetrical spherical or aspherical components (off-axis section), non-standard rotating symmetrical profiles such as cones, arcs or any other shape, and the FO component conforms to the geometry of the system. FO creates new opportunities for optical designers, while also presenting challenges to fabrication technology and measurement methods. FO is widely used in the fields of green technology, solid lighting, aerospace, agriculture and biomedical. FO components have the potential to revolutionize the optical industry, so now this is an active research field in terms of both fundamental and applied research as well as the development of processing tools, measurement, shown through the number of more than 230 important publications, hundreds of patents and industrial products in recent times. 1.2.2. FO applications in solid state lighting The application of FO components in LED-based solid state lighting technology is one of the most important in recent years due to the benefits of solid state lighting technology in combination with FO. However, the design of a non-imaging optical system requires a new approach, especially because of the variety of optical characteristics of different types of LEDs. In the field of interior lighting, there are many studies focusing on the design and application of smart lighting systems using LEDs 5 [49-51, 78-92], however the non-uniformity of luminance distribution is still the weakness of solid lighting systems. Integrating FO lenses with LED light sources for the purpose of evenly illuminating the ceiling is a trend that attracts a lot of attention from designers. 1.3. Lighting 1.3.1. Human vision Recent research results show that the human eye is not only for seeing, but also a means of connecting the human internal biological clock with the Earth's rotation and the solar system. In urban life, when artificial lighting environment is different from natural light in length, spectral structure, there is no signal at the beginning and the end of day, circadian rhythm will be reversed and has many consequences for physical, physiological and mental health. 1.3.2. Lighting pollution In modern times and in big cities, people spend more and more time in artificial lighting environments. The difference between artificial light environment and natural light environment can be considered as light pollution. As a result of these differences is one of the causes of nearsightedness (myopia) and other human physiological ailments such as poor performance, depression, insomnia, heart disease, weight gain and even cancer [45]. Light pollution factors derive from the limited functionality of the light source types, as well as due to weaknesses in lighting design. 1.3.3. Human centric lighting 6 HCL-Human Centric Lighting- is the most important topic and most actively discussed today, as the industrial revolution 4.0 comes to life. Recent studies also show that the huge difference between the natural light environment and the artificial light environment is one of the causes of various types of distortion such as myopia, amblyopia, and sleep, amnesia, depression, infertility ... [46, 59-64]. Scientists, R&D centers of lighting companies have many researches, looking for new human centric lighting solutions, that is, creating artificial lighting environments that are close to the natural light environment that consistent with human circadian rhythms [106-109]. In this thesis, I will focus on the research, design and fabrication of new light sources based on LED light sources integrated with FO components to solve pressing problems in lighting such as glare, inconvenience, loss of rhythm, protect eyesight and health for users. CHAPTER II. METHOD, TECHNIQUES AND TECHNOLOGY 2.1. Calculate, design and simulate using assistant software We used specialized software such as Excel, Origin to calculate and analyze data, especially in the process of processing measurement data of fluorescence spectra, reflection spectrum, transmission spectrum... To design optical or mechanical components, we have chosen Solidworks software to design lens profiles, light trays and auxiliary details such as headlamps, suspension bars... After designing the lens profile, we conducted optical simulation to evaluate the light redistribution efficiency of the optical 7 lens system using optical simulation software such as Optgeo, Tracepro, Zeemax... 2.2. Techniques and technology 2.2.1. Fabricating FO prototypes After designing the structure for FO components, we fabricate FO prototypes using one of two technologies: CNC cutting from PMMA materials and 3D printing using transparent optical material. The prototype after creating has many defects, which needs to be completed by 3 methods: grinding and polishing; processing temperature; optical coating. Experimental results for the optical coating method gave the best results. 2.2.2. FO manufacture using plastic injection molding technology We use only thermoplastic injection technology in the manufacture of FO lenses and other optical components in our LED luminaire production chain. The chosen materials for use depend on the needs and specific use of the product. Specifically, the asymmetrical and narrow lens sample is manufactured from PS material, while the lens for fish lamps uses PC material. 2.2.3. Aluminum extrusion technology For large-scale production, aluminum casting technology and aluminum extrusion technology are used instead of CNC machine tool cutting technology. We choose to design linear lamps with the aim of saving costs, creating a competitive advantage when wanting to commercialize the product. 8 2.3. Measurement and evaluated method 2.3.1. Methods and equipment for measuring characteristics of materials We have used some methods and equipment of the Key Laboratory of the Institute of Materials Science to measure the characteristics of materials and components. Fluorescence measurement system investigates the emission spectrum of phosphor materials for LEDs. To determine the gloss of FO components after thermoplastic injection molding, the FSEM scanning electron microscope is a suitable device. Usually the gloss of optical components is about λ/5 to λ/10 equivalent to 100nm to 50nm. 2.3.2. Equipment for measuring characteristics of LED light suorces Intergrating sphere measuring system is a combination of measuring devices including: intergrating sphere, spectrometer, luminous flux probe, computer with display software support, used to measure optical - electrical parameters of the light source. Goniophotometer: is a device for measuring the distribution of light intensity with angle. Measurements are standardized and stored in IES format, where the luminance (unit of measure cd) is a function of the projection angle. 2.4. Lighting model installation Simulating the lighting environment using Dialux Evo software We used Dialux Evo simulation software to calculate the lighting options for buildings to make the best choice. The actual