A(2)B(n–1)Pb(n)I(3n+1) (A = BA, PEA; B = MA; n = 1, 2): Engineering Quantum-Well Crystals for High Mass Density and Fast Scintillators

[Image: see text] Quantum-well (QW) hybrid organic–inorganic perovskite (HOIP) crystals, e.g., A(2)PbX(4) (A = BA, PEA; X = Br, I), demonstrated significant potentials as scintillating materials for wide energy radiation detection compared to their individual three-dimensional (3D) counterparts, e.g., BPbX(3) (B = MA). Inserting 3D into QW structures resulted in new structures, namely A(2)BPb(2)X(7) perovskite crystals, and they may have promising optical and scintillation properties toward higher mass density and fast timing scintillators. In this article, we investigate the crystal structure as well as optical and scintillation properties of iodide-based QW HOIP crystals, A(2)PbI(4) and A(2)MAPb(2)I(7). A(2)PbI(4) crystals exhibit green and red emission with the fastest PL decay time <1 ns, while A(2)MAPb(2)I(7) crystals exhibit a high mass density of >3.0 g/cm(3) and tunable smaller bandgaps <2.1 eV resulting from quantum and dielectric confinement. We observe that A(2)PbI(4) and PEA(2)MAPb(2)I(7) show emission under X- and γ-ray excitations. We further observe that some QW HOIP iodide scintillators exhibit shorter radiation absorption lengths (∼3 cm at 511 keV) and faster scintillation decay time components (∼0.5 ns) compared to those of QW HOIP bromide scintillators. Finally, we investigate the light yields of iodide-based QW HOIP crystals at 10 K (∼10 photons/keV), while at room temperature they still show pulse height spectra with light yields between 1 and 2 photons/keV, which is still >5 times lower than those for bromides. The lower light yields can be the drawbacks of iodide-based QW HOIP scintillators, but the promising high mass density and decay time results of our study can provide the right pathway for further improvements toward fast-timing applications.