Probing the structure, morphology and multifold blue absorption of a new red-emitting nanophosphor for LEDs

Abstract

There has been a stringent demand for blue (∼450 to 470 nm) absorbing and red (∼611 nm) emitting material systems in phosphor converted white light emitting diodes (WLEDs) available in the market. The conventionally used red-emitting Y2O3:Eu3+ phosphor has negligible absorption for blue light produced by GaInN based LED chips. To address this issue, a new red-emitting Gd2CaZnO5:Eu3+ (GCZO:Eu3+) nanophosphor system having exceptionally strong absorption for blue (∼465 nm) and significant red (∼611 nm) photoluminescence is presented. This is attributed to a dominant f–f transition (5D0 → 7F2) of Eu3+ ions, arising due to an efficient energy transfer from the Gd3+ sites of the host lattice to Eu3+ ions. The external quantum yield (QY) measured at 465 nm absorption and 611 nm emission revealed that the GCZO:Eu3+ nanophosphor has better QY of 23% as compared to commercial Y2O3:Eu3+, which is <1%. X-ray diffraction and microscopy observations showed the nanocrystalline nature and slightly elongated morphology of the sample, respectively. While the energy dispersive X-ray analysis identified the chemical constituents of the GCZO:Eu3+ nanophosphor, the color overlay imaging confirmed the substitution of Eu3+ for Gd3+ ions. As seen from the QY statistics it is highly anticipated that the multifold absorption at ∼465 nm would certainly improve the color rendering properties of existing WLEDs.