In dilute phosphoric acid solutions, cadmium (Ⅱ) reacts with excess of Ⅰ^- to form [CdI4]^2- anionic complex, which may further react with basic xanthene dyes (BXD) such as rhodamine B(RhB), rhodamine 6G(Rh6G), ethylrhodamine B(ERhB), or butylrhodamine B (RhB) to form an ion-association complex of type [BXD]2[CdI4]. In this case, a strong frequency-doubling scattering (FDS) and significant second- order scattering (SOS) are produced. Under optimal conditions, the intensities of FDS and SOS are directly proportional to the concentration of cadmium. The method has high sensitivity and fair selectivity and can be applied to direct determination of trace amounts of cadmium in pure zinc. In this paper, the reasons for producing FDS and SOS are preliminarily discussed.

Key words: CADMIUM, IODIDE, SCATTERING, RHODAMINE B