InP-Quantum-Dot-in-ZnS-Matrix Solids for Thermal and Air Stability

InP/ZnS core/shell colloidal quantum dots (QDs) are promising candidates as Cd- and Pb-free emitters owing to their high photoluminescence quantum yield, narrow emission linewidth, and color tunability in the visible range. However, the stability of QD solid films remains an issue: they are vulnerable to oxygen, moisture, and heat. Here, we report the encapsulation of InP/ZnS QDs in a lattice-matched ZnS matrix. We do so by developing a biphasic ligand exchange and uniting it with a sol–gel film assembly. Conventional ZnS precursors, which rely on neutral thiourea, fail to stabilize the QDs in highly polar solvents, leading to their agglomeration prior to matrix formation. Here, we substitute thiourea with ammonium thiocyanate—an ionic compound isomer of thiourea—to stabilize InP/ZnS QDs in a ZnS matrix precursor solution. The stabilized QD and precursor solution is then cast and annealed to trigger the formation of a homogeneous and robust ZnS matrix that protects the QDs. The resulting QD solid films show invariant optical properties following annealing at 200 °C for 1 h under ambient conditions, under continuous laser excitation at 60 mW cm–2 for 180 min, and also after a month of storage under ambient conditions. In contrast, the control film exhibits significant degradation of its optical properties after annealing at 200 °C for 1 h, under laser excitation within 20 min, and under ambient conditions within 10 days.