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

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 O-states 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/m², 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.