Iodide Nanocrystal Scintillator Simulator

Material

Parameters

Photon energy Eγ 60 keV

Activator quality η_bulk 35%

Nanocrystal size D 10 nm

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Scintillation photons

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Light yield

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Energy resolution (FWHM)

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How it works

An incident gamma/X-ray photon of energy Eγ is photoelectrically absorbed by the iodide lattice, ejecting a fast photoelectron that loses its energy by ionizing the crystal — creating a cascade of electron-hole pairs. The mean energy needed per pair is an empirical multiple (Robbins' rule, factor β ≈ 2–3) of the material's bandgap Eg. Each pair then migrates to an activator/luminescence centre, where a fraction η recombines radiatively into a visible scintillation photon:

N_eh = Eγ / (β·Eg)          (electron-hole pairs)
η_eff = η_bulk · D/(D + d_q) (surface-quenched in a nanocrystal)
N_ph = η_eff · N_eh          (scintillation photons)
LY   = N_ph / Eγ             (light yield, photons/MeV)
R    = 235% / √N_ph          (Poisson-limited energy resolution, FWHM)

Material — sets the bandgap Eg and pair-creation factor β. A narrower gap (perovskite) makes each pair cheaper to create, but its softer lattice loses more energy to phonons (higher β), so the two effects partly cancel.
Photon energy Eγ — more deposited energy makes more electron-hole pairs and, because light yield is per-unit-energy, a larger absolute photon burst; energy resolution improves (smaller R) at higher Eγ since photon statistics improve as √N.
Activator quality η_bulk — the bulk-crystal fraction of pairs that recombine radiatively rather than being lost to non-radiative traps.
Nanocrystal size D — this is what makes it a genuinely nano-scale effect: shrinking the crystal raises its surface-to-volume ratio, and surface trap states quench a growing share of the light (d_q ≈ 2.5 nm quenching length here), so η_eff falls sharply below a few nm even if η_bulk stays the same.

Real-world relevance: this photoelectric → cascade → recombination → readout chain is exactly what happens inside a CsI:Tl or NaI:Tl gamma detector, and it is why nanocrystal scintillators (including iodide perovskites) need careful surface passivation to keep their light yield competitive with bulk crystals.

Lattice ion Incident photon Electron-hole pair Scintillation photon

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