Efficient energy transfer from inserted CdTe quantum dots to YVO ₄:Eu³⁺ inverse opals: A novel strategy to improve and expand visible excitation of rare earth ions

Rare earth (RE)-based phosphors demonstrate sharp emission lines, long lifetimes and high luminescence quantum yields; thus, they have been employed in various photoelectric devices, such as light-emitting diodes (LEDs) and solar spectral converters. However, their applications are largely confined by their narrow excitation bands and small absorption cross sections of 4f-4f transitions. In this paper, we demonstrate a novel strategy to improve and expand the visible excitation bands of Eu³⁺ ions through the interface energy transfer (ET) from CdTe quantum dots (QDs) to YVO ₄:Eu³⁺ inverse opal photonic crystals (IOPCs). The significant effects observed in the CdTe QDs/YVO₄:Eu³⁺ IOPCs composites were that the excitation of Eu³⁺ ions was continuously extended from 450 to 590 nm and that the emission intensity of the ⁵D₀-⁷F_J transitions was enhanced ∼20-fold, corresponding to the intrinsic ⁷F₁- ⁵D₁ excitation at 538 nm. Furthermore, in the IOPC network, the ET efficiency from the QDs to YVO₄:Eu³⁺ was greatly improved because of the suppression of energy migration among the CdTe QDs, which gave an optimum ET efficiency as high as 47%. Besides, the modulation of photonic stop bands (PSBs) on the radiative transition rates of the QDs and Eu³⁺ ions was studied, which showed that the decay lifetime constants for Eu³⁺ ions were independent of PSBs, while those of QDs demonstrated a suppression in the PSBs. Their physical nature was explained theoretically.