Semiconductors luminescence

There is a growing need to sense molecules for applications as diverse as waste management, explosives detection, and disease prevention. Goals of chemical sensor development are to create devices that require little power and that are robust, sensitive, selective, fast, compact, and inexpensive. In this chapter, we describe optical techniques based on semiconductor luminescence that are promising methods for chemical sensing applications. 

The application of semiconductor luminescence to chemical sensing can rely on the chemical, electrical, and optical properties of II-VI and III-V semiconductors [1]. These properties provide the binding capability, transducing mechanism, and signal required for chemical sensing. The diverse chemical compositions of semiconductor materials provide a range of surfaces for molecular binding. 

The transducing mechanism of semiconductor luminescence involves the modification of the semiconductors surface electrical properties through molecular adsorption. Changes in solid-state electro-optical properties result from adsorption of the molecule of interest onto the semiconductor surface. 

Temperature plays an important role in semiconductor luminescence. In general, as temperatures decrease, band-gap luminescence increases in intensity and decreases in wavelength by 0.2-0.3 nm/°C [20], Joule heating in the LEDs can result in significant thermal effects that will limit their usefulness as chemical... 

In semiconductor phosphors the energy band structure of the host crystal plays a central role. Some semiconductor luminescence arises from decay of exciton states, other emission arises from decay of donor states generated by impurity or defect centers. It is not the magnitude of the band gap itself that separates insulator from semiconductor phosphors it is a question of whether the spectrum is characteristic of impurity energy levels as perturbed by the local crystal structure or whether the spectrum is characteristic of the band structure as modified by impurities. 

S.2.3. Conductivity, superconductivity, semiconductors, luminescence Without going into details we will just cite a number of research groups that recently have investigated superconductivity, [82] conductivity, [83] semi-... 

Keywords Nanoparticies, Synthesis, Characterization, ll-VI Semiconductors, Luminescence... 

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

Finally, an electric current can produce injection luminescence from the recombination of electrons and holes in the contact 2one between differendy doped semiconductor regions. This is used in light-emitting diodes (LED, usually ted), in electronic displays, and in semiconductor lasers. 

CL smdies are performed on most luminescent materials, including semiconductors, minerals, phosphors, ceramics, and biological—medical materials. 

Spatial information about a system can be obtained by analyzing the spatial distribution of PL intensity. Fluorescent tracers may be used to image chemical uptake in biological systems. Luminescence profiles have proven useftil in the semiconductor industry for mapping impurity distributions, dislocadons, or structural homogeneity in substrate wafers or epilayers. Similar spatial infbrmadon over small regions is obtained by cathodoluminescence imaging. 

Nonstoichiometric oxide phases are of great importance in semiconductor devices, in heterogeneous catalysis and in understanding photoelectric, thermoelectric, magnetic and diffusional properties of solids. They have been used in thermistors, photoelectric cells, rectifiers, transistors, phosphors, luminescent materials and computer components (ferrites, etc.). They are cmcially implicated in reactions at electrode surfaces, the performance of batteries, the tarnishing and corrosion of metals, and many other reactions of significance in catalysis. ... 

R.E. Gill, Design, Synthesis and Characterization of Luminescent Organic Semiconductors, Ph.D. Thesis, Groningen, 1996. 

McMurray L, Holmes AJ, Kuperman A, Ozin GA, Ozkar S (1991) IntrazeoUte semiconductors sodium-23 MAS NMR, thallium(l+) luminescence quenching and far-IR studies of acid-base precursor chemistry in zeolite Y. J Phys Chem 95 9448-9456... 

Spanhel L, Haase M, Weller H, Henglein A (1987) Photochemistry of colloidal semiconductors. 20. Surface modification and stability of strong luminescing CdS particles. J Am Chem Soc109 5649-5655... 

Maenosono, S., Dushkin, C. D., Saita, S. and Yamaguchi, Y. (2000) Optical memory media based on excitation-time dependent luminescence from a thin film of semiconductor nanocrystals. Jpn. J. Appl. Phys., 39, 4006- 12. 

In this paper we will describe and discuss the metal-to-metal charge-transfer transitions as observed in optical spectroscopy. Their spectroscopic properties are of large importance with regard to photoredox processes [1-4], However, these transitions are also responsible for the color of many inorganic compounds and minerals [5, 6], for different types of processes in semiconductors [7], and for the presence or absence of certain luminescence processes [8]. 

F. F. Volkenshtein, A.N. Gorban and V.A. Sokolov, Combination Luminescence in Semiconductors, Nauka Publ., cow, 1976... 

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