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.