Luminescent Materials
This chapter surveys the field of solid-state luminescent materials, beginning with a discussion of the different ways in which luminescence can be excited. The internal energy-level structures of luminescent ions and centres, particularly rare-earth ions
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Luminescent 40. Luminescent Materials
This chapter surveys the field of solid-state luminescent materials, beginning with a discussion of the different ways in which luminescence can be excited. The internal energy-level structures of luminescent ions and centres, particularly rareearth ions, are then discussed before the effects of the vibrating host lattice are included. Having set the theoretical framework in place, the chapter then proceeds to discuss the specific excitation process for photo-stimulated luminescence and thermally stimulated luminescence before concluding by surveying current applications, including plasma television screens, long-term persistent phosphors, X-ray storage phosphors, scintillators, and phosphors for white LEDs.
40.1.3 s2 Ions ..................................... 987 40.1.4 Semiconductors ........................ 987 40.2 Interaction with the Lattice.................. 987 40.3 Thermally Stimulated Luminescence ...... 989 40.4 Optically (Photo-)Stimulated Luminescence ..................................... 990 40.5 Experimental Techniques – Photoluminescence ............................. 991 40.6 Applications ........................................ 40.6.1 White Light-Emitting Diodes (LEDs) ...................................... 40.6.2 Long-Persistence Phosphors ....... 40.6.3 X-Ray Storage Phosphors ........... 40.6.4 Phosphors for Optical Displays .... 40.6.5 Scintillators ..............................
992 992 992 993 994 994
40.1 Luminescent Centres ............................ 985 40.1.1 Rare-Earth Ions ........................ 985 40.1.2 Transition-Metal Ions ................ 986
40.7 Representative Phosphors .................... 995
Luminescent materials are substances which convert an incident energy input into the emission of electromagnetic waves in the ultraviolet (UV), visible or infrared regions of the spectrum, over and above that due to
black-body emission. A wide range of energy sources can stimulate luminescence, and their diversity provides a convenient classification scheme for luminescence phenomena, which is summarised in Table 40.1. Pho-
References .................................................. 995
Table 40.1 Types of luminescence Excitation
Trigger
Acronym
Photoluminescence
UV, visible photons X-ray, gamma rays, charged particles Energetic electrons Electric field Photons, charged particles Photons, charged particles
–
PL
–
RL
–
CL
– Heat
EL TSL
Visible/IR photons
OSL, PSL
Radioluminescence
Cathodoluminescence Electroluminescence Thermoluminescence
Optically/photo-stimulated luminescence
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Designation
984
Part D
Materials for Optoelectronics and Photonics
2
Excited state P23 3
P12
1
Luminescing state
P31NR
P31R
Ground state
Fig. 40.1 Optical pumping cycle for a generic photolumi-
nescent system
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toluminescence, where the luminescence is stimulated by UV or visible light, is a widely used materials science technique for characterising dopants and impurities, and finds applications in lighting tech
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