Halide-Perovskite Nanocrystal Photoluminescence: Quantum-Confined Emission Tuning

Nanocrystal

Diameter d 6.0 nm

Halide mix (Cl ↔ Br ↔ I) Br

Excitation

405 nm pump intensity 70%

Surface traps (ligand loss) 20%

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Bulk gap E_g0

2.30 eV

Confinement ΔE

0.14 eV

Total bandgap

2.44 eV

Emission λ

508 nm

Photons emitted

PLQY

Pump status

absorbing

405 nm pump photon

Electron (conduction)

Hole (valence)

Emitted PL photon

Trapped (non-radiative)

How it works

Lead-halide perovskite nanocrystals (CsPbCl₃ / CsPbBr₃ / CsPbI₃ and their halide-mixed alloys) are colloidal quantum dots: shrinking the crystal below roughly the exciton Bohr radius (~3-5 nm for this family) confines the electron and hole to a box, raising the bandgap by a particle-in-a-box term that scales as 1/d². Because the halide sublattice sets the bulk gap almost independently of size, chemists tune emission color two ways at once — anion exchange (Cl → Br → I) shifts the bulk gap from ~3.1 eV (violet, CsPbCl₃) to ~2.3 eV (green, CsPbBr₃) to ~1.7 eV (red, CsPbI₃), and size-controlled synthesis adds a blue confinement shift on top. This is the real synthesis lever behind "size- and composition-tunable" perovskite LEDs and displays.

E_g(d,x) = E_bulk(x) + K / d²      (Brus-style confinement, K ≈ 5 eV·nm²)
E_bulk: 3.10 eV (Cl) → 2.30 eV (Br) → 1.73 eV (I)
absorption needs E_pump(3.06 eV, 405 nm) ≥ E_g
λ_emit = 1240 / E_g (nm)
PLQY = radiative decays / (radiative + trapped)

Diameter — smaller dots confine carriers harder, blue-shifting emission (1/d² scaling).
Halide mix — anion-exchange composition; sets the underlying bulk gap the confinement term rides on top of.
Pump intensity — rate of 405 nm photons arriving; only absorbed if their 3.06 eV energy still exceeds the current bandgap (shrink a Cl-rich dot enough and the pump stops working entirely — watch the pump status readout).
Surface traps — fraction of excitons that lose energy non-radiatively at unpassivated surface defects instead of emitting a photon, exactly the ligand-shell quality that controls real photoluminescence quantum yield (PLQY).

pump 405 nm e⁻ h⁺ PL photon