Deep Blue and Highly Emissive ZnS-Passivated InP QDs: Facile Synthesis, Characterization, and Deciphering of Their Ultrafast-to-Slow Photodynamics

Abstract

InP-based quantum dots (QDs) are an environment-friendly alternative to their heavy metal-ion-based counterparts. Herein we report a simple procedure for synthesizing blue emissive InP QDs using oleic acid and oleylamine as surface ligands, yielding ultrasmall QDs with average sizes of 1.74 and 1.81 nm, respectively. Consecutive thin coating with ZnS increased the size of these QDs to 4.11 and 4.15 nm, respectively, alongside a significant enhancement of their emission intensities centered at ∼410 nm and ∼430 nm, respectively. Pure phase synthesis of these deep-blue emissive QDs is confirmed by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Armed with femtosecond to millisecond time-resolved spectroscopic techniques, we decipher the energy pathways, reflecting the effect of successive ZnS passivation on the charge carrier (electrons and holes) dynamics in the deep-blue emissive InP, InP/ZnS, and InP/ZnS/ZnS QDs. Successive coating of the InP QDs increases the intraband relaxation times from 200 to 700 fs and the lifetime of the hot electrons from 2 to 8 ps. The lifetime of the cold holes also increase from 1 to 4 ps, and remarkably, the Auger recombination escalates from 15 to 165 ps. The coating also drastically decreases the quenching by the molecular oxygen of the trapped charge carriers at the surfaces of the QDs. Our results provide clues to push further the emission of InP QDs into more energetically spectral regions and to increase the fluorescence quantum yield, targeting the construction of efficient UV-emissive light-emitting devices (LEDs).

Surface Passivation toward Multiple Inherent Dangling Bonds in Indium Phosphide Quantum Dots

“…The lifetime τ 2 value of InP with NH 4 PF 6 treatment is lower than that of the pristine InP QDs, which displayed substantially higher radiative decay rates. 31 The NH 4 PF 6 effect with varied concentrations toward the InP core and InP/ZnSe QDs continues to be investigated and the results are reported in Figure S6 and Table S2. The lifetime contribution c 1 value of NH 4 PF 6 -treated InP core and resultant InP/ZnSe QDs at ∼0.30 M is smaller than those of the other two samples, which suggests the sufficient peel-off and Previously, the P−DBs were eliminated, and the emission associated with defects was subsequently decreased, as previously stated.…”

Blue-emitting InP quantum dots participate in an efficient resonance energy transfer process in water

“…Instead, they form a quasi-type-II core-shell QDs. 36 As the shell thickness is less, the excitons will be mainly conned within the InP core. 36,42 As a result, the PL QY will be high, and the PL maxima will be centered around the band edge emission of the core QDs (∼462 nm in the present study).…”

“…36 As the shell thickness is less, the excitons will be mainly conned within the InP core. 36,42 As a result, the PL QY will be high, and the PL maxima will be centered around the band edge emission of the core QDs (∼462 nm in the present study). A thicker shell will lead to the delocalization of the electron wave function to the shell, which compromises the photophysical properties of the QDs.…”

“…28 A few protocols are available to prepare blueemitting InP QDs in organic medium, wherein the growth kinetics of QDs is slowed down by controlling the reaction temperature, precursor reactivity, surface etching, shell growth, competitive secondary nucleation process, etc. [29][30][31][32][33][34][35][36] In one example, stable blue-emitting InP/ZnS/ZnS QDs (l em ∼475 nm) were prepared by ne-tuning the inherent reactivity between phosphorus and indium precursors, thereby achieving a control Department of Chemistry, Indian Institute of Science Education and Research (Pune), Dr Homi Bhabha Road, Pashan, Pune -411008, India. E-mail: pramod.pillai@ iiserpune.ac.in † Electronic supplementary information (ESI) available: Detailed experimental methods, synthesis, and characterization of QDs, stability studies, bioimaging, uptake mechanism, proof of electrostatics and calculation of various parameters involved in the FRET study.…”

“…28 A few protocols are available to prepare blueemitting InP QDs in organic medium, wherein the growth kinetics of QDs is slowed down by controlling the reaction temperature, precursor reactivity, surface etching, shell growth, competitive secondary nucleation process, etc. [29][30][31][32][33][34][35][36] In one example, stable blue-emitting InP/ZnS/ZnS QDs (l em ∼475 nm) were prepared by ne-tuning the inherent reactivity between phosphorus and indium precursors, thereby achieving a control over nucleation and growth processes. 33 This has led to the development of efficient blue-emitting light emitting diodes (LEDs) based on InP/ZnS/ZnS core/shell/shell QDs.…”