明亮，高效且颜色稳定的紫色ZnSe基量子点发光二极管资源-CSDN文库

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本篇研究论文介绍了一种新型的“低温注入和高温生长”方法合成的高稳定性紫蓝色发射的ZnSe/ZnS核/壳量子点。该论文探讨了这些量子点的合成方法、表征以及在发光二极管（QD-LEDs）中的应用。知识点一：ZnSe基量子点的合成方法文中提到的“低温注入和高温生长”方法是一种新颖的合成策略，用于制备具有优异特性的ZnSe/ZnS核/壳结构量子点。该方法能够有效控制量子点的大小和表面结构，从而达到高度单分散性。这个合成过程对于提高量子点在光电器件中的性能至关重要。知识点二：ZnSe基量子点的光电特性研究中合成的ZnSe/ZnS核/壳量子点表现出高颜色饱和度、良好的发射可调性、高绝对光致发光量子产率以及优越的化学和光化学稳定性。颜色饱和度通常指的是光谱全宽度半高最大值（FWHM）在12到20纳米之间，而良好的发射可调性意味着可在400到455纳米的紫蓝色范围内进行调节。这些都是量子点作为发光材料的关键性能指标。知识点三：紫光量子点发光二极管(QD-LEDs) 论文展示了基于ZnSe/ZnS量子点的无镉(Cd)量子点发光二极管(QD-LEDs)，其最大亮度可达2632 cd/m²，峰值外量子效率（EQE）可达7.83%。这些器件的亮度和效率不仅是先前无镉QD-LEDs的12倍效能提升和100倍亮度提升，而且其性能还远超基于镉的紫光QD-LEDs的最佳性能1.7%。这一突破性进展展现了短波长QD-LEDs的显著进步，并为环保型紫光QD显示屏的商业化应用指明了方向。知识点四：环境友好型量子点的应用研究中介绍的无镉量子点技术的开发，相较于传统的含镉量子点，具有环境友好型的优势。研究的成功表明，不仅可以在不牺牲器件性能的前提下减少环境污染，还能够推动量子点在光电器件和显示屏技术中的应用，特别是短波长波段的器件。知识点五：半导体量子点的尺寸依赖性光学特性在研究半导体量子点时，尺寸依赖性光学特性是一个关键概念，它指的是量子点的光学性质与其尺寸有很强的相关性。这种性质使得量子点可以在高光通量下实现优异的光谱纯度。量子点的尺寸调整可以实现从紫外到红外光谱范围的精确发射波长控制，这一特性使得它们成为LED和显示设备的潜在明星材料。总结来说，这篇论文对ZnSe基量子点的合成工艺进行了研究，探讨了量子点的光电特性，并展示了其在无镉紫光QD-LEDs中的应用潜力。研究指出，新的量子点合成方法及特性展示对于推动环保型短波长QD显示技术的商业化进程具有重要意义。此外，论文还强调了半导体量子点的尺寸依赖性光学特性对于改善光电器件性能的重要作用。

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Nanoscale

PAPER

Cite this: Nanoscale, 2015, 7, 2951

Received 8th November 2014,

Accepted 4th January 2015

DOI: 10.1039/c4nr06593j

www.rsc.o rg/nanoscale

Bright, eﬃcient, and color-stable violet

ZnSe-based quantum dot light-emitting diodes†

Aqiang Wang,

Huaibin Shen,*

a,b

Shuaipu Zang,

Qingli Lin,

Hongzhe Wang,

a,b

Lei Qian,

Jinzhong Niu

and Lin Song Li*

a,b

In this paper, highly stable violet-blue emitting ZnSe/ZnS core/shell QDs have been synthesized by a

novel “low temperature injection and high temperature growth” method. The resulting nearly monodis-

perse ZnSe/ZnS core/shell QDs exhibit excellent characteristics such as a high color saturation (typical

spectral full width at half-maximum between 12 and 20 nm), good emission tunability in the violet-blue

range of wavelengths from 400 to 455 nm, a high absolute PL quantum yield (up to 83%), and superior

chemical and photochemical stability. By employing ZnSe/ZnS core/shell quantum dots (QDs) as emitters

with a fully solution processable method, bright, eﬃcient, and color-stable violet Cd-free quantum dot-

based light-emitting diodes (QD-LEDs) with maximum luminance up to 2632 cd m

−2

and a peak EQE of

7.83% have been demonstrated successfully. Considering the factors of the photopic luminosity function,

the brightness and eﬃciency results of such violet QD-LEDs not only represent a 12-fold increase in

device eﬃciency and an extraordinary 100 times increase in luminance compared with previous Cd-free

QD-LEDs but also can be much superior to the best performance (1.7%) of their Cd-based violet counter-

parts. These results demonstrate signiﬁcant progress in short-wavelength QD-LEDs and shed light on

the acceleration of commercial application of environmentally-friendly violet QD-based displays and

lighting.

Introduction

Colloidal semiconductor quantum dots (QDs) have attracted

much attention due to their unique size-dependent optical

properties which can achieve excellent spectral purity at high

optical flux. Their excellent optical properties make them

potential superstars in light-emitting diodes (LEDs) and

displays.

1–7

To fully exploit the potential of QDs in these appli-

cations, researchers need to synthesize materials that

simultaneously meet the following five criteria: narrow and

symmetric emission spectra, high photoluminescence (PL)

quantum yields (QYs), high optical stability, eco-friendly

materials, and low-cost methods for mass production. Most of

the previous studies on highly emissive and color-tunable QDs

have mainly concentrated on materials containing toxic

cadmium, mercury, or lead.

8–16

For example, red light emitters

of CdSe/CdS QDs with QYs up to 90%,

green region emitters

of CdSe/ZnS/CdSZnS QDs with the best QYs of 100% and

improved photo- and chemical-stabilities,

and the QYs of

1−x

S/ZnS QDs also reached almost unity even in the

violet-blue region.

However, there are increasing concerns that

these toxic materials such as cadmium, lead, and mercury

would pose serious threats to human health and the environ-

ment, and the European Union’s Restriction of Hazardous

Substances (RoHS) rules ban any consumer electronics con-

taining more than trace amounts of these materials.

The

likelihood of commercial success for quantum dot-based light-

emitting diodes (QD-LEDs) and displays will therefore be

greatly improved if the devices can be fabricated using

eco-friendly and heavy-metal-free QDs.

Most of the syntheses of non-toxic or low toxicity QDs are

now focused on I–III–VI semiconductors (such as CuInS

18–22

III–V semiconductors (such as InP),

23–26

and II–VI semi-

conductors (such as ZnSe and rela ted Cu-, Mn-doped ZnSe),

27–31

which have low-toxicity, tunable emissions in the visible-to-

near-infrared region. The current QYs for the CuInS

core/shell

QDs is up to 60%, but the emission tunability is mainly con-

fined between 540 and 650 nm.

20,21

The obtained III–V heavy-

metal-free QDs typically possess emissions from 480 to

600 nm with the highest QYs up to 70%.

24,25

Most recently, the

† Electronic supplementary information (ESI) available. See DOI: 10.1039/

c4nr06593j

Key Laboratory for Special Functional Materials of Ministry of Education,

Henan University, Kaifeng 475004, China. E-mail: shenhuaibin@henu.edu.cn,

lsli@henu.edu.cn

Collaborative Innovation Center of Nano Functional Materials and Applications,

Henan Province, P. R. China

This journal is © The Royal Society of Chemistry 2015 Nanoscale,2015,7,2951–2959 | 2951

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QD-LEDs fabricated based on low toxicity QDs also showed

some progress. The maximum brightness utilizing I–III–VI

semiconductor QDs have reported over 1000 cd m

−2

in the

yellow-red area without the demonstration of external

quantum eﬃciency (EQE).

21,32

For those using the III–V heavy-

metal-free QDs, such as InP/ZnSeS QDs, the maximum EQE

can reach more than 3% with an electroluminescence (EL)

peak at 518 nm and show a full width at half-maximum

(FWHM) of about 64 nm.

These results demonstrate good

color tunability and competitive eﬃciencies for heavy-metal-

free QD-LEDs in the range of 510 to 630 nm, but still lack good

results on the violet-blue emission QD-LEDs due to the

absence of corresponding heavy-metal-free QD emitters. There-

fore, one of the main challenges is the development of

eﬃcient violet-blue emitters and the realization of higher

eﬃciency QD-based LEDs using heavy-metal-free QDs.

So far, for the heavy-metal-free QDs, no matter I–III–VI or

III–V QDs, all cannot obtain high QYs (>70%) and high stabi-

lity QDs in the violet-blue area, let alone high brightness and

eﬃciency of corresponding violet-blue QD-LEDs. Most recent

studies have begun to concentrate on the synthesis of wide

bandgap ZnSe QDs as potential violet-blue emitter. Our pre-

vious report showed an impressively high QY of 70%,

but the

stability of ZnSe related QDs is still unsatisfied. Previously

reported red-green and Cd-containing blue QD emitters

showed QYs of up to 90% with high stabilities,

14–16

and these

results all indicate the immediacy of the QY and stability

improvement of violet-blue ZnSe QDs. Therefore, the synthesis

of violet-blue QDs that can simultaneously satisfy high PL QYs

(>80%), narrow and symmetric emission (FWHM < 20 nm),

high stability, environmentally friendliness, and low cost is an

urgent requirement for the realization of heavy-metal-free

violet-blue and thus full-color QD-LEDs. Herein, we present a

method for the synthesis of violet-blue emitting ZnSe/ZnS

core/shell QDs that show high QYs as well as high stability.

Diﬀerent from most of the traditional nucleation at high temp-

erature/shell growth at low temperature methods, we adopt a

lower temperature injection and higher temperature growth

method for the synthesis of ZnSe/ZnS core/shell QDs.

14–16

Nearly monodisperse ZnSe/ZnS core/shell QDs were syn-

thesized with high absolute PL QYs (up to 80%), high color

purity (with an FWHM of about 12–20 nm), and good color

tunability in the violet-blue range from 400 to 455 nm.

Importantly, such ZnSe/ZnS core/shell QDs showed very good

chemical/photochemical stability compared with previous

studies.

27,30

Furthermore, violet QD-LEDs using ZnSe/ZnS core/shell

QDs have also been successfully demonstrated with a fully

solution-processed method. Highly bright violet QD-LEDs

show a maximum luminance of 2632 cd m

−2

and a peak EQE

of 7.83%. In a sense, such brightness and eﬃciency exhibit

huge superiority to those of the best Cd-based violet-blue

QD-LEDs considering the factors of the photopic luminosity

function. These results may oﬀer a practicable platform for the

realization of heavy-metal-free QD based violet-blue and full-

color displays and lighting.

Experimental section

Chemicals

All reagents were used as received without further experi-

mental purification. Zinc oxide (ZnO, 99.99% powder), sulfur

(S, 99.98%, powder), 1-octadecene (ODE, 90%), oleic acid (OA,

90%), octanethiol (OT, 98%), zinc acetate (99.99%), dimethyl

sulphoxide (DMSO, 99.7%), tetramethylammonium hydroxide

(TMAH, 97%), and selenium (Se, 99.99%, powder) were pur-

chased from Aldrich. Chlorobenzene (analytical grade),

hexanes (analytical grade), paraﬃn oil (analytical grade), and

methanol (analytical grade) were obtained from Beijing Chemi-

cal Reagent Ltd, China.

Typical synthesis of ZnSe/ZnS with low temperature

nucleation/high temperature shell growth method

Stock solution for the Zn precursor: A mixture (20 mL in total) of

ZnO (0.488 g, 6 mmol), oleic acid (18 mmol, 5.076 g), and

14 mL paraﬃn oil was loaded in a 100 mL three-necked flask

and heated to 300 °C under nitrogen to obtain a clear solution.

Zn precursor solution was stored at 120 °C for subsequent use.

Stock solution for the Se precursor: Se (0.237 g, 3 mmol) and

30 mL of ODE were mixed in a 100 mL three-necked flask.

Under nitrogen flow and stirring, the mixture was heated to

220 °C for 180 min, and then the reaction solution was cooled

down to room temperature. Se precursor solution was stored at

50 °C for subsequent use. Synthesis of ZnSe QDs with lower

temperature and synthesis of ZnSe/ZnS core/shell QDs with high

temperature: octanethiol as the S precursor and ligands for the

synthesis of ZnSe/ZnS core/shell QDs: The ZnSe core was pre-

pared according to the previous literature of our group (see

ESI†).

In a typical synthesis, 2 mL Se precursor and 8 mL

paraﬃn oil were heated to 300 °C under nitrogen flow in a

100 mL flask. Next, 1.3 mL Zn precursor solution was injected

and maintained for 5 min for the formation of ZnSe core QDs

(Fig. S1† and Fig. 1a). Subsequently, the reaction temperature

was set at 320 °C without any purification steps, and then

2 mL OT mixed with 20 mL of Zn precursor was added at a rate

of 6 mL h

−1

. All the shell growth processes lasted for 4 h.

Aliquots of QDs were taken during the reaction to analyze the

development of ZnSe/ZnS core/shell QDs (Fig. 1). After the

reaction was completed, the temperature was cooled down

to room temperature and the QDs were purified using acetone

or methanol. ZnSe/ZnS core/shell QDs with diﬀerent

shell growth temperatures (as shown in Fig. 3) were prepared

following the same procedures as that described above for the

synthesis of ZnSe/ZnS core/shell QDs at 320 °C, with a range

of diﬀerent growth temperatures of 240 °C, 260 °C, 280 °C,

300 °C, and 340 °C, respectively (see ESI †). S-ODE as the

S precursor for the synthesis of ZnSe/ZnS core/shell QDs: the syn-

thesis of ZnSe/ZnS core/shell QDs with S-ODE as the S pre-

cursor was similar to the aforementioned method, except that

octanethiol was replaced by conventional S-ODE (0.2 M) as the

S precursor.

Paper Nanoscale

2952

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