Advancement in materials for energy-saving lighting devices Author Kim, Tak H, Wang, Wentai, Li, Qin Published 2012 Journal Title Frontiers of Chemical Science and Engineering DOI https://doi.org/10.1007/s11705-011-1168-y Copyright Statement © 2012 Springer-Verlag Berlin Heidelberg. This is an electronic version of an article published in Frontiers of Chemical Science and Engineering, Vol. 6(1), pp. 13-26, 2012. Frontiers of Chemical Science and Engineering is available online at: http://link.springer.com/ with the open URL of your article. Downloaded from http://hdl.handle.net/10072/53008 Griffith Research Online https://research-repository.griffith.edu.au Front. Chem. Sci. Eng. DOI 10.1007/s11705-011-1168-y 1 REVIEW ARTICLE 1 5 Advancement in materials for energy-saving lighting devices 5 Tak H. KIM, Wentai WANG, Qin LI (✉) 10 10 Department of Chemical Engineering, Curtin University, Perth 6845, Australia © Higher Education Press and Springer-Verlag Berlin Heidelberg 2012 15 15 Abstract This review provides a comprehensive account and can be categorized into general lighting and specia- of energy efficient lighting devices, their working lized lighting. General lighting refers to both indoor and principles and the advancement of these materials as an outdoor lighting which is the most common form of underpinning to the development of technology. Particular lighting. Specialized lighting refers to lighting with more 20 attention has been given to solid state lighting devices and specific areas and functionalities. Figure 1 shows lighting 20 their applications since they have attracted the most devices categorized by their applications. interest and are the most promising. Solid state lighting Fluorescent lamps have been used in offices and homes devices including white light emitting diodes (LEDs), as a low-cost, energy-saving light source for more than 60 organic LEDs (OLEDs), quantum-dot LEDs (QLEDs) and years and are a good alternative to incandescent lamps. 25 carbon-dot LEDs (CLEDs) are promising energy efficient Fluorescent lamps represent a significant advancement in 25 lighting sources for displays and general lighting. However technology since they consume 2–5 times less power and there is no universal solution that will give better last 8–10 times longer than incandescent lamps. However, performance and efficiency for all types of applications. lighting technologies have continued to develop in order to LEDs are replacing traditional lamps for both general bring more efficient lighting as well as to minimize 30 lighting and display applications, whereas OLEDs are environmental hazard issues [2]. 30 finding their own special applications in various areas. Lighting devices emit photons of different wavelength QLEDs and CLEDs have advantages such as high ranges, depending on the luminescent material used and quantum yields, narrow emission spectra, tunable emission the mechanism for light generation. White light emitting spectra and good stability over OLEDs, so applications for devices are currently in high demand because of the fast 35 these devices are being extended to new types of lighting growing electronic display industry. Unlike old-type 35 sources. There is a great deal of research on these materials cathode ray tubes, liquid crystals do not emit light and their processing technologies and the commercial themselves, so they need a light source called a backlight viability of these technologies appears strong. unit in order to function as display devices [3,4]. Due to the enormously increasing demand for large and small 40 Keywords energy-saving lighting devices, solid state displays, there are huge needs for better quality backlight 40 lighting devices units. Large display devices such as TVs are becoming bigger and hence they need brighter and more efficient backlighting devices; whereas small display devices such 1 Introduction as mobile phones and notebook computers require more 45 energy efficient backlights for better battery life. 45 One fifth of global power consumption is used for lighting White light emitting devices such as fluorescent lamps [1], therefore, it is very important to develop energy-saving were initially developed for general lighting as well as for lighting devices as part of an energy sustainability strategy. industrial lighting [5–7]. Although it has been more than New generations of lighting devices are continually being 100 years since fluorescent lamps (FL) were initially 50 developed owing to discoveries and advancements in new utilized for lighting applications, the growth of information 50 materials and lighting technologies. Lighting devices have technology and the related display technologies has been utilized in various forms and for various applications brought new demands for quality white lights and better lighting devices. At the time when thin film transistor (TFT) LCD display devices first became commercially 55 Received August 20, 2011; accepted November 18, 2011 available in the late 1980s, there were not many choices for 55 E-mail: [email protected] backlights and compared to incandescent lamps, FLs were FCE-11068-KT.3d 5/1/012 15:18:40 2 Front. Chem. Sci. Eng. 1 1 5 5 10 10 Fig. 1 Types of lighting applications and types of lamps used (FL: fluorescent lamp; HID: high intensity discharge; CCFL: cold cathode fluorescent lamp; EEFL: external electrode fluorescent lamp; LED: light emitting diode; OLED: organic light emitting diode; QLED: quantum-dot light emitting diode; CLED: carbon-dot light emitting diode) 15 15 the better choice due to their better energy efficiencies and better efficiencies and lifetimes than carbon-filament more suitable emission spectra [3,7]. incandescent bulbs. The development of efficient long- Because of the fast development of material technolo- lasting electrodes and suitable fluorescent phosphor gies and their related processing technologies, conven- materials to convert the invisible ultraviolet light into 20 tional types of FLs are disappearing fast and being replaced visible light made these lamps a commercial reality in the 20 by solid state lamps as backlighting devices [8]. These 1940s. Since then fluorescent lighting has been used in solid state lamps are promoted as being higher efficiency offices and homes as a low-cost, energy-saving light andbetterqualitythanFLs.However,sofartheir source. In addition FLs have been further developed as a applications are very limited in display areas because of light source for LCD display devices. 25 their higher costs and because of current technical barriers Most FLs use mercury vapor along with a small amount 25 such as size limitations and fast blue color degradation of an inert gas mixture [12–17]. The inner surface of the [9,10]. tube is coated with a phosphor. The other key element is In this review, a comprehensive account of energy the electrodes. When the fluorescent lamp is on, a large efficient lighting devices, their working principles and the number of free electrons are generated from the electrodes. 30 advancement of these materials as a key driver in the The electrons migrate through the gas from one end of the 30 development of technology is provided. Particular atten- tube to the other. As the electrons and charged atoms move tion is placed on solid state lighting devices and their through the tube, some of them collide with the gaseous applications since they have attracted the most interest and mercury atoms. These collisions excite the electrons in the are the most promising. Figure 2 presents the typical mercury atoms into higher energy levels. When the 35 varieties of solid state lamps and their applications. All electrons return to their original energy level, they emit 35 these newly developed lighting devices are considered to UV photons. The UV light is then absorbed by the be promising technologies. phosphor and reemitted as visible light. The amount of light emitted from the tube depends on the phosphor used. The wavelengths radiated by the 40 2 Fluorescent lamps phosphor vary with the chemicals used to make the 40 phosphor. For instance, the phosphor used in FLs are It has been more than 100 years since the first mercury generally halo-phosphates which contain calcium, anti- vapor lamp was patented by Hewitt [11] His lamps have mony, chlorine, fluorine and manganese [18]. been widely used for industrial lighting because they have FLs are generally categorized by the electrode type, as 45 45 50 50 55 Fig. 2 Types of solid state lamps and their applications (LED: light emitting diode, OLED: organic light emitting diode, QLED: 55 quantum-dot light emitting diode, CLED: carbon-dot light emitting diode) FCE-11068-KT.3d 5/1/012 15:18:40 Tak H. KIM et al. Advancement in materials for energy-saving lighting devices 3 1 1 5 5 10 10 Fig. 3 Fluorescent lamps and their applications 15 15 illustrated in Fig. 3. There are many electrode types with light uniformity when it is applied as the light source for different shapes and materials but for FLs there are mainly LCD panels [3,27–29]. two types of operational modes. FLs that use coiled Although cold cathode lamps offer better performance tungsten can be categorized as hot cathode lamps; these than conventional FLs and CFLs, they require a discharge 20 operate at high temperatures to liberate electrons and are tube and a tube that contains at least a milligram of 20 the most common type. The other type is a cold cathode FL mercury. Mercury-free discharge lamps which utilize a (CCFL) which operates at high voltage to liberate phosphor and plasma technology have been designed to electrons. As shown in Fig. 4, unlike conventional FLs replace mercury filled systems. A xenon gas mixture is a or compact fluorescent lamps (CFLs), the cathodes used in well-known alternative plasma source, however it is not as 25 CCFLs are metals that are constructed to maximize surface efficient as mercury and is much more expensive [27,30].