Activating room temperature phosphorescence by organic materials using synergistic effects

Abstract

Designing highly effective organic room temperature phosphorescent (ORTP) materials presents great technical challenges due to their weak spin–orbit coupling and intense non-radiative transitions. Herein, we employ layered double hydroxides (LDHs) as a host matrix, and present a design principle to activate ORTP of carbon dots (CDs) through three synergistic effects. Impressively, the obtained Zn-CDs-LDHs present high phosphorescence quantum yield (PQY) of up to 9.58% and ultralong RTP lifetime of 719.9 ms at ambient conditions, which is higher than those of most reported CD-based materials. Activated ORTP originates from: (1) structural confinement provided by the nanospaces of LDHs reduces the non-radiative decay of triplet excitons and boosts the T₁ → S₀ radiative relaxation; (2) non-noble metal Zn(II) in LDH interlayer disturbs the symmetry of triplet excitons and antisymmetry of singlet excitons by strong spin–orbit coupling and enhances the intersystem crossing (ISC) from the singlet excited state (S_n) to the triplet manifold (T_n); and (3) chemical bonding (coordination, covalent, electrostatic, and hydrogen bonding) between the rigid LDH matrix and the interlayer CDs. Design strategies that account for such synergistic effects will open new avenues for the development of advanced ORTP phosphors with ultralong lifetimes.