Realization of Excitation Wavelength Independent Blue Emission of ZnO Quantum Dots with Intrinsic Defects

Abstract

Ecofriendly cation metal oxide quantum dots (QDs) are one of the promising candidates to replace for QDs containing expensive indium (In) or hazardous Cd-and Pb-elements. Super-E g excitation wavelength (λ ex ) dependent Zn i -V O complex defects related characteristic emissions of green, yellow, and orange-red from ZnO QDs are completely inhibited by reducing oxygen vacancies through the hybridization of Zn interstitials in ZnO QDs with antibonding Ostates of graphene oxide (GO) QDs. Thus, only λ ex independent violet-purple-blue (V-P-B) emission resulting from transitions among Frenkel pairs (Zn i 0 -V Zn ) and the defects Zn i 0 -O i in ZnO-GO QDs with a high photoluminescence quantum yield (PLQY) of 92% is successfully achieved. White-light emission from PL QD-LEDs is achieved using a mixture of ZnO and ZnO-GO QDs with CIE (0.32, 0.34) excited by a UV LEDs chip (λ = 365 nm). Further, ZnO-GO QD-based deep-blue LEDs (λ = 438 nm) with luminance of 1980 cd/m 2 , a luminous efficacy (LE) of 2.53 cd/ A, and external quantum efficiency (EQE) of 2.78% with CIE (0.16, 0.11) are also realized.

Journey of ZnO quantum dots from undoped to rare-earth and transition metal-doped and their applications

“…11g is helpful in explaining the PL emission spectra of the composite. 16 Some researchers have fabricated the ZnO-silica composite using tetraethoxysilane (TEOS). Recently, Liang et al 76 have mixed different amounts of ZnO QDs in the aqueous solution of TEOS.…”

“…11 (a-d) Illustration of ZnO-GO formation, (e and f) PL spectra of the ZnO-GO composite and (g) the energy level of the ZnO-GO composite. 16 Adapted with permission from ref. 16.…”

“…1) is provided for detailed information about the synthesis, properties, and applications of ZnO QDs. Hence, ZnO shows a wide range of applications in material engineering, health science, 9 drug delivery 10,11 photocatalyst, gas sensors, 12 cancer therapy [13][14][15] photoelectric light-emitting diodes (LED), [16][17][18] solar cells, 19 and photo-detectors. 20 Quantum connement [21][22][23] is a major aspect of QD that keeps it at the next level compared to nanoparticles.…”

“…Copyright (2014) American Scientific. (g) ZnO-GO based QLED, (h) energy level diagram, (i) EL spectra of the ZnO-GO-based device 16. Adapted with permission from ref 16…”

“…(k) Current density and luminance vs. voltage. (l) Luminous efficacy and external quantum efficiency (EQE) vs. voltage and (m) 100 pixel display of the ZnO-GO-based QLED 16. Adapted with permission from ref 16…”