Oxygen vacancy induced luminescence in Y2Zr2O7 and its removal on Eu3+ doping leading to enhanced quantum efficiency

Abstract

To circumvent the low color rendering index and high color temperature of existing white light emitting diodes (LEDs), a lot of attention has been given on designing efficient red emitting luminophores for phosphor converted LEDs (pcLEDs). Utilizing the favorable properties of Y2Zr2O7 (YZO) pyrochlore and Eu3+ as dopant ion we could produce bluish white light emitting YZO and red light emitting YZO:Eu3+ (YZOE). Based on monoexponential luminescent decay, we could infer europium ion occupies Y3+ site which is in line with density functional theory (DFT) calculated defect formation energy and positron annihilation lifetime spectroscopy (PALS). YZO on UV irradiation generates bluish white light endowed by both neutral and singly ionized oxygen vacancies but with very meager photoluminescence quantum yield (PLQY∼1.2%). On doping Eu3+ ion in YZO; oxygen vacancy is completely removed with efficient host to dopant energy transfer leading to bright red emission with PLQY∼ 8.2%. The feasibility of YZO to Eu energy transfer is well established using DFT calculations. Reduction in density of oxygen vacancies on doping is well corroborated using electron paramagnetic resonance (EPR) and thermoluminescence (TL) spectroscopy and very well supported by DFT calculations. In this work by harnessing the potential of pyrochlore lattice defects and doping engineering we could enable almost 8-fold increase in PLQY in YZOE.