BOOK_CONTENT
From Chromic Phenomena: Technological Applications of Colour Chemistry

3.6 Chemiluminescence

Chemiluminescence is the production of light by chemical substances without the help from other energy sources; in effect it is the conversion of energy stored in chemical bonds into light. Mechanistically, chemiluminescence involves several consecutive processes. The first step is the chemical reaction to form a product, which can undergo further highly exothermic transformations of sufficient energy to emit light in the visible region (400 700 nm) of the spectrum. For this to occur the reaction enthalpy must be in excess of 40 kcal mol ?1. In the second step, chemical potential energy is transformed into electron excitation energy by a reaction intermediate entering an electronically excited state. The final step is the loss of energy from this excited state, as fluorescence or phosphorescence depending on whether the orientation of the spin in the excited intermediate is singlet or triplet (see Figure 3.1). This is called direct Chemiluminescence as opposed to indirect Chemiluminescence in which the electronically excited state transfers energy to a suitable acceptor which itself emits light.

3.6.1 Chemiluminescent Reactions

The most useful chemiluminescent reactions fall into three categories.1 ,48

  • Reactions involving electron transfer. Reaction of free ion radicals, oxidation of anion radicals of aromatic and heteroaromatic hydrocarbons. Usually an energy acceptor is required to be present

  • Reactions of singlet oxygen. Singlet oxygen, e.g. generated by the action of chlorine on alkaline hydrogen peroxide, transfers its energy to a fluorophore acceptor, which emits light

  • Peroxide decomposition. Singlet oxygen can also...

Copyright The Royal Society of Chemistry 2001 under license agreement with Books24x7

Products & Services
Hardness Testers
Hardness testers measure a material's resistance to indentation. This calculation is determined by measuring the permanent depth or projected area of the indentation.
Linear Shafts
Linear shafts are elongated, rod-shaped devices that provide linear or rotary motion for power transmission applications.
Rotary Shafts
Rotary shafts are elongated, rod-shaped devices that rotate about a longitudinal axis and transmit torque. They are similar in shape to linear shafts, but are designed to withstand torsional forces.
Product and Material Test Fixtures and Accessories
Material test fixtures and accessories include mechanical testing grips, fixtures, sample heaters, extensometers, specimen cutters, and other specialized test components.
Durometers
Durometers are instruments used for measuring the indentation hardness of rubber, elastomers, plastics and foam materials.

Topics of Interest

3.7 Bioluminescence Bioluminescence is the production of light by living systems. The best-known example of this phenomenon is the characteristic glow of the firefly, but other luminous species...

Vickers and Knoop hardness testers can be used for Micro and Macro hardness testing. Typically loads are very light, ranging from a few grams to one or several kilograms, although "Macro" Vickers...

The Rockwell hardness test is one of several common indentation hardness tests used today, other examples being the Brinell hardness test and Vickers hardness test. Most indentation hardness tests are...

Material property analysis and hardness measurement provide a broad spectrum of data to a wide variety of markets. Traditionally hardness has been defined as the resistance of a material to permanent...

The Rockwell test method is defined in ASTM E-18 and is the most commonly used hardness tester operation method since it is generally easier to perform and more accurate than other types of hardness...

Product Announcements
Tinius Olsen, Inc.
Ametek Test & Calibration Instruments
Ametek Test & Calibration Instruments