CeMgAl₁₁O₁₉:Tb³⁺ is a green phosphor used in tricolor fluorescent lights.

Figure 7.25

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Ce+ ions in the host absorb photons from the Hg-plasma discharge with an excitation max- imum near 270 nm and emit via a [Xe]4f05d [Xe]4f transition with a Stokes shift of 0.9 eV. The Tb+ dopant emits via f-to-f transitions from a D, excited state to various F, levels (see Figure 7.25), with a maximum near 540 nm. (a) At what wavelength will the emission maximum of the Ce+ ion fall? (b) Which lanthanoid ion is responsible for the green light? Why is the other lanthanoid ion needed? (c) What mechanism is responsible for energy transfer between Ce+ and Tb*?