Synthesis of luminescent phosphors for lighting devices and other applications

Abstract

Luminescence is the process in which emission of light occurs due to newlinethe influence of radiations. Luminescence can be broadly classified into two newlinetypes, namely fluorescence and phosphorescence. Fluorescence occurs within newlinea very short time usually, less than 10-8 newlinesec following photo excitation since newlinethe electronic transition in this case are allowed transitions as per Laporte newlineselection Rule. Phosphorescence refers to delayed emission. The time delay newlinebetween photo-excitation and emission can be of the order of micro sec, milli newlinesec, sec, min, hours or even more. The delay occurs since the emission occurs newlinebetween forbidden electronic states. Phosphor is a Greek word meaning light newlinebearer. The word phosphor (and phosphorescence) is used to refer to newlineluminescent substances. newlineThe application of photoluminescent phosphors is in fluorescent lamps, newlinecathode ray tubes, scintillating materials, speciality lamps, Light Emitting newlineDiodes (LED), Optical data storage and luminescent paint. Scintillators work newlineby converting ionizing radiation energy into visible light so that the high newlineenergy radiation can be detected easily with photomultipliers which are newlinesensitive to visible light. A large variety of special lamps are used widely newlinebecause phosphor materials with any emission spectra can be designed for use newlinein speciality lamps used in photocopy machines, bill boards, plant newlineillumination, skin disease treatment (psoriasis) etc. Due to improved newlineluminescence efficiency, Hg based fluorescent lamps (FL) replaced newlineincandescent lamps a few decades ago. However, the toxicity of Hg and other newlineissues such as high power consumption, delayed start and temperature newlinedependent light emission are some of the shortcomings of these lamps newline