Cation-Exchange-Derived InGaP Alloy Quantum Dots toward Blue Emissivity

Abstract

In contrast to a substantial progress of heavy metal-free green and red emitters exclusively from indium phosphide (InP) quantum dots (QDs), the development of non-Cd blue QDs remains nearly unexplored. The synthesis of blue InP QDs with a bright, deep-blue emissivity is not likely viable, which is primarily associated with their intrinsic size limitation. To surmount this challenge, herein, the first synthesis of blue-emissive ternary InGaP QDs through In3+-to-Ga3+ cation-exchange strategy is implemented. Pregrown InP QDs turn out to be efficiently Ga-alloyed at a relatively low temperature of 280 °C in the presence of Ga iodide (GaI3), and the degree of Ga alloying is also found to be systematically adjustable by varying GaI3 amounts. Such cation-exchanged InGaP cores are surface-passivated sequentially with ZnSeS inner and ZnS outer shells. As the amount of GaI3 added for cation exchange increases, the resulting double-shelled InGaP/ZnSeS/ZnS QDs produce consistent blue shifts in photoluminescence (PL) from 475 to 465 nm, while maintaining high PL quantum yield in the range of 80–82%. Among a series of QD samples, above 465 nm emitting InGaP/ZnSeS/ZnS QDs are further employed as an emitting layer of an all-solution-processed electroluminescent device. This unprecedented InGaP QD-based blue device generates maximum values of 1038 cd/m2 in luminance and 2.5% in external quantum efficiency.

Highly Bright, Narrow Emissivity of InP Quantum Dots Synthesized by Aminophosphine: Effects of Double Shelling Scheme and Ga Treatment

“…Thus, such a spectral shift, albeit slight, is reliable. We presume that in the presence of Ga species, the partial In 3+ ‐to‐Ga 3+ cation exchange at the surface of InP core likely occurs, [ 6,32 ] especially when its amount is surplus. As a consequence, the effective core size of as‐synthesized InP/ZnSe/ZnS QD shrinks, inducing the stronger quantum confinement effects and thus a blue‐shift in PL.…”

“…Meanwhile, synthesis of high‐quality blue‐emitting InP QDs is relatively challenging, being associated with their tiny core sizes well below 2 nm, usually resulting in only quasi‐blue color (>475 nm in PL peak) beyond deep‐blue territory (450−465 nm). [ 4,5 ] Therefore, InP QDs are regarded as the strongest candidates for green and red color, while blue emitters can be pursued from either ternary InGaP [ 6 ] or non‐InP ZnSeTe QDs. [ 7–9 ]…”

Synergistic Effect of Halogen Ions and Shelling Temperature on Anion Exchange Induced Interfacial Restructuring for Highly Efficient Blue Emissive InP/ZnS Quantum Dots

“…Considering the slow surface reaction rates of iodide ions, InI 3 and ZnI 2 are utilized to prepare blue emissive InP QDs with emission below 475 nm in recent studies. [ 27,28 ] By the way, Ga doping is also regarded as an effective method to realize short wavelength emission. [ 29,30 ] Unfortunately, the blue emissive InP QDs still lag much behind red and green emissive InP QDs.…”

Advances and Challenges in Heavy-Metal-Free InP Quantum Dot Light-Emitting Diodes

“…However, the simultaneous nucleation and crystal growth in the direct synthesis strategy leads to a non-uniform grain size distribution [ 40 ]. To solve this problem, the researchers proposed seeded growth strategies [ 6 , 41 ] and the cation exchange method [ 42 , 43 , 44 ]. The seeded growth method first pre-synthesizes InP QDs seeds and then uses additional In and P precursors for further growth to obtain uniform InP QDs, as shown in Figure 1 c. Due to the good controllability of the size, morphology, and uniformity of InP QDs, seed growth is a better choice for obtaining high-quality InP QDs.…”