Chemical Education Today
Letters Chemistry and Luminescence
The authors reply:
The article “Turning on the Light: Lessons from Luminescence” (1) offers a succinct, yet rigorous, treatment of the most relevant luminescent phenomena such as fluorescence and phosphorescence, or tribo-, chemi- and bioluminescence. The authors have, however, ignored a relevant and unique process: sonoluminescence, the weak emission of light flashes by bubbles in a liquid excited by sound (a pressure wave). Sonoluminescence was first reported in the early 1930s, although it was not considered important in that time (2). The phenomenon can be observed for both aqueous and nonaqueous liquids, and generally at ultrasonic frequencies (beyond 20 kHz). Sonoluminescence arises from cavitation, i.e. the formation, growth and collapse of microbubbles, which produces excited state species (3). Although both cavitation and sonoluminescence are complex and nonlinear phenomena, which have been the subject of mathematical models, common ultrasonic devices are convenient and inexpensive tools to detect their effects. Applications of ultrasound have been occasionally discussed through this Journal as a means of improving synthetic (4) or environmental (5) procedures and many readers could certainly benefit from this additional information. In addition, ultrasound can also enhance the well-known chemiluminescence derived from the oxidation of luminol (6). The experiment can easily be conducted in an ultrasonic bath, well suited for undergraduate courses.
We thank Dr. Cintas for highlighting yet another process by which materials can be induced to emit light. Our discussion of light emission was not meant to be exhaustive, but to discuss some of the most well known processes and accessible techniques. Patricia B. O’Hara Department of Chemistry Amherst College Amherst, MA 01002-5000
[email protected] Literature Cited 1. O’Hara, P.; Engelson, C.; St. Peter, W. J. Chem. Educ. 2005, 82, 49. 2. Frenzel, H.; Schultes, H. Z. Phys. Chem. 1934, B27, 421. 3. (a) Crum, L. A.; Roy, R. A. Science 1994, 266, 233; (b) Brenner, M. P.; Lohse, D.; Dupont, T. F. Phys. Rev. Lett. 1995, 75, 954. 4. Lash, T. D.; Berry, D. J. Chem. Educ. 1985, 62, 85. 5. Wilmer, B. K.; Poziomek, E.; Orzechowska, G. E. J. Chem. Educ. 1999, 76, 1657. 6. Mason, T. J. Practical Sonochemistry; Ellis Horwood: New York, 1991; p 65. Pedro Cintas Departamento de Química Orgánica Universidad de Extremadura E-06071 Badajoz, Spain
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Vol. 82 No. 6 June 2005
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Journal of Chemical Education
837
