Transformation from a Weak- to strong-size confinement regime in PbI2 ultra-thin microcrystallites embedded in E-MAA copolymer

Transformation from weak- to strong-size confinement has been observed in a time-resolved photoluminescence (PL) of PbI 2 ultra-thin microcrystallites embedded in ethylene-metacrylic acid (E-MAA) copolymer. At 2 K, there appears a PL line that originates from an exciton state bound to a neutral donor. The temporal behavior of the PL intensity has two exponential decay components. In microcrystallites that are thicker than 5 layers, the decay time of the slow component (τ slow ) becomes longer as the thickness decreases and has a maximum value at around 5 layers. The decay time decreases with further decrease in thickness. The thickness dependence of τ slow was explained both by a giant oscillator strength of the bound exciton and by shrinkage of the exciton wave function.