X-ray induced fluorescence measurement of segregation in a DyI₃–Hg metal-halide lamp

Abstract

Segregation of elemental Dy in a DyI3–Hg metal-halide high-intensity discharge lamp has been observed with x-ray induced fluorescence. Significant radial and axial Dy segregation are seen, with the axial segregation characterized by a Fischer parameter value of λ = 0.215 ± 0.002mm−1. This is within 7% of the value (λ = 0.20±0.01mm−1) obtained by Flikweert et al (2005 J. Appl. Phys. 98 073301) based on laser absorption by neutral Dy atoms. Elemental I is seento exhibit considerably less axial and radial segregation. Some aspects of the observed radial segregation are compatible with a simplified fluid picture describing two main transition regions in the radial coordinate. The first transition occurs in the region where DyI3 molecules are in equilibrium with neutral Dy atoms. The second transition occurs where neutral Dy atoms are in equilibrium with ionized Dy. These measurements are part of a larger study on segregation in metal-halide lamps under a variety of conditions.