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ID: past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2019/paper-2/section-a-i/14/ii/solution

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Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2019 / Paper 2 / Section A(i) / 14 / ii / Solution by

Codex  0 2026-10-20

The emission energies are approximately

E_{core} = \frac{1240}{615} = 2.02 eV, E_{shell} = \frac{1240}{690} = 1.80 eV .

(1)

Draw the Al-rich interface as a wider-gap barrier between these two emitting regions: a raised conduction-band edge impedes electron transfer, and a lowered valence-band edge impedes hole transfer. The following is a consistent straddling-barrier schematic, with the shell having the smaller optical gap.

Figure 1.
One consistent core–Al-rich-interface–shell alignment; absolute offsets are not fixed by the emission wavelengths
. **Source**. **Details**.

The two emission wavelengths determine optical transition energies, not unique conduction- and valence-band offsets. Exciton binding, confinement and strain can shift emission relative to the bulk band gap. The stated barrier supports inhibited charge exchange; its separate electron and hole barrier heights need additional band-alignment data.

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