Phosphors 2 Luminescent Lighting

These bricks, after calcination with carbon and exposure to daylight, emitted a reddish glittering in the dark. These Bolonian stones, also named moonstones, particularly those from the Monte Patemo, remain among the most famous ones and were the subject of scientific interest during the next two centuries they were termed phosphor (Greek light bearer ). They are considered the first inorganic artificial phosphors [2-4], The first natural phosphor was dia-mant, whose luminescence was cited by Cellini in 1568 [5]. 

For over 50 years the phosphors of choice for luminescent lighting have been based on activated calcium halophosphates, Ca3(PO )3X (where X = F, Cl), the usual activators being Sb " and Mn ". When Sb " is used as the dopant the phosphor is a very efficient blue emitter under 254 nm excitation, whilst Mn shows an orange... 

Tungsten chemicals find limited use in inks, paints, enamels, dyes, and glass manufacture. Some tungsten compounds and their derivative phosphors find use in x-ray screens, television picture tubes, and luminescent light sources. 

Another application that benefits from the small pores and large inner surface of aerogels are photo-luminescent light sources [83]. Until now, in these devices a radioactive gas (e.g., tritium) was let into a glass tube coated with a phosphor at the inner surface. Integrating the phosphor in an aerogel of low density increases both the intensity and total output of the system. 

Luminescent lighting started even before the Second World War. The ultraviolet radiation from a low-pressure mercury dischaige is converted into white light by a phosphor layer on the inner side of the lamp tube. These lamps are much more efficient than the incandescent lamp a 60 W incandescent lamp yields 15 Im/W, a standard 40 W luminescent lamp 80 Im/W. 

OSL could also be used for container verification. Luminescent phosphor additives, ionized by radiation, are mixed with paints or clear coats and are applied to the surface of a container (Miller et al. 2009). The OSL phosphors luminesce in proportion to the ionization radiation dose and the intensity of excitation light. The OSL coatings/additives will be invisible to the naked eye, but could be seen using an InGaAs infrared detector. The OSL additives would tag the container and reveal an attempt to tamper with the container and therefore increase the confidence that its integrity had not been compromised. 

Yeh CW, Liu YP, Xiao ZR, Wang YK, Hu SF, Liu RS (2012) Luminescence and density functional theory (DFT) calculation of undoped nitridosilicate phosphors for light-emitting diodes. J Mater Chem 22 5828... 

Various phosphors have been developed for different application systems, wherein the oxide phosphors are particularly noticed and mosfly widely used because of their excellent properties such as high luminescence efficiency and thermal stability as well as the superiority of simple preparation methods and inexpensive raw materials. In this chapter, oxide phosphors for lighting and display will be introduced, and more attention will be focused on the performance improvement of practical oxide phosphors for three-band fluorescent lamps, plasma displays, and white light-emitting diodes. Due to the space limitation, the aim of this chapter is not to discuss all of the works involved in the progress of oxide phosphors but to introduce the efforts made by our research group in the General Research Institute for Nonferrous Metals, China. 

Nagpure IM, Pawade VB, Dhoble SJ (2010) Combustion synthesis of Na2Sr(P04)F Dy white light emitting phosphor. Luminescence 25 9... 

A prediction was made in early 1970s that a luminescent lamp with a high efficiency and high light quality could be obtained by combining three phosphors (luminescent materials) which emit in narrow wavelength intervals centered around 450 nm (blue), 550 nm (green), and 610 nm (red). Immediately, it was clear that phosphors doped with lanthanide ions were the most obvious choice to construct this tricolor luminescent lamp. 

Nonradiative Decay. To have technical importance, a luminescent material should have a high efficiency for conversion of the excitation to visible light. Photoluminescent phosphors for use in fluorescent lamps usually have a quantum efficiency of greater than 0.75. AH the exciting quanta would be reemitted as visible light if there were no nonradiative losses. 

Luminescent Pigments. Luminescence is the abihty of matter to emit light after it absorbs energy (see Luminescent materials). Materials that have luminescent properties are known as phosphors, or luminescent pigments. If the light emission ceases shortly after the excitation source is removed (<10 s), the process is fluorescence. The process with longer decay times is referred to as phosphorescence. 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

Zinc compounds are generally colorless unless the other component, eg, chromate, is colored. The lack of color of most zinc compounds in visible light is a great advantage in that they do not color paint films, plastics, mbber, cosmetics, etc. However, when excited by various types of radiation and at various temperatures, zinc oxide, sulfide, selenide [1315-09-9], and related compounds exhibit luminescence, ie, they emit colored light (see Luminescent materials). Zinc-based phosphors can be produced in many colors, depending upon the added dopants. They are used in television tubes, luminescent glasses, and various specialty products. 

Image plates use stimulated luminescence from storage phosphor materials. The commercially available plates are composed of extremely fine crystals of BaFBrEu2+. X-rays excite an electron of Eu2+ into the conduction band, where it is trapped in an F-center of the barium halide with a subsequent oxidation of Eu2+ to Eu3+. By exposing the BaFBrEu" complex to light from a HeNe laser the electrons are liberated with the emission of a photon at 390 nm [38]. 

The understanding of phosphors and solid-state luminescence has matured to the point at which relatively rational design and preparation of new light-emitting materials can be achieved. This has resulted from advances in solid-state physics and optical spectroscopy coupled to the development of new chemical synthesis techniques. This has led to the rapid development of phosphors as important industrial/technological materials. Examples of the occurrence of phosphors in everyday use include ... 

The delayed light emission as observed from the Bolonian stone is now classified as phosphorescence. We know now that these stones contain barium sulfate with traces of bismuth and manganese, and that the corresponding reducing process concerns the transformation of sulfate into sulfur. It is now well known that alkaline earth metal sulfates emit phosphorescence that strongly increases when traces of heavy metals are present. The so-called inorganic multi-component compounds phosphor and crystallophosphor are in fact polycrystalline substances containing traces of some ionic activators of luminescence. 

---