An exciton is a bound electron-hole pair that originates, diffuses and dissociates inside—or at the interface of—a crystal. Direct observation of excitons is difficult :
Because the [negative] electron and the positive hole have equal but opposite electrical charges, the exciton as a whole has no net electrical charge (though it transports energy). This makes excitons difficult to detect, but detection is possible by indirect means.The adjective excitonic is used to specify materials or devices in which excitons can occur or play a critical role in their function. An excellent example are excitonic solar cells for converting light into electrical energy [5,6]. No surprise, there is a lot of excitement about excitons.
The English noun exciton in other languages
German: Exziton (neuter)
 Allon I. Hochbaum and Peidong Yang: Semiconductor Nanowires for Energy Conversion. Chem. Rev. 2010, 110, pp. 527-546 (see pages 531 to 536 on excitonic solar cells).
 Brian A. Gregg: The Photoconversion Mechanism of Excitonic Solar Cells. MRS Bulletin January 2005, 30, 20-22. PDF.