Harnessing　supramolecular　interactions　to　regulate　the　structure　and　performance　of　functional　materials　is　a　key　challenge　in　materials　chemistry.　Herein,　the　study　utilizes　18-crown-6　(18C6)　ether-assisted　alkali-metal　(Na,　K,　Cs)　copper(I)　iodide　supramolecular　assemblies　to　precisely　regulate　the　material　structures.　This　approach　facilitated　the　transition　from　1D　mono-royal　crown　coordination　(18C6@KCuI2,　CKCI)　to　0D　di-royal　crown　((18C6)2@Na2(H2O)3Cu4I6,　CNCI)　and　tri-royal　crown　((18C6)3@Cs2Cu2I4,　CCCI)　structures.　Interestingly,　the　CCCI　single-crystal　exhibits　outstanding　scintillation　properties,　with　a　high　relative　light　yield　of　71 000　photons　MeV−1　and　an　ultralow　detection　limit　of　39.3　nGy　s−1,　which　can　be　attributed　to　the　synergistic　effects　of　18C6　and　copper-iodide　clusters.　It　stabilizes　the　self-trapped　exciton　state,　enhances　exciton　localization,　and　reduces　non-radiative　losses,　thus　resulting　in　a　large　Stokes　shift　of　193 nm　and　near-unity　photoluminescence　quantum　yield　of　99.4%.　Additionally,　18C6　can　promote　crystal　nucleation　and　growth,　making　it　easy　to　prepare　centimeter-scale　transparent　single　crystals　with　＞80%　transmittance,　such　as　CCCI　single　crystal　can　achieve　an　ultrahigh-resolution　X-ray　imaging　of　26.3　lp　mm−1.　It　demonstrates　that　the　structure　and　performance　of　halide　scintillators　can　be　regulated　through　supramolecular　interactions,　which　provides　a　new　approach　for　developing　high-performance　scintillator　materials.　©　2025　Wiley-VCH　GmbH.