Search

Fe3+ ions as near‐infrared (NIR) activators are emerging as an alternative to Cr3+.1–5 However, it is a challenge to develop Fe3+‐activated NIR phosphors featuring tunable optical properties, high efficiency, and thermal stability. Herein, we present a series of near‐unity internal quantum efficiency (IQE), wavelength‐tunable and thermal stability NIR‐emitting phosphors Sr2−yCaySc1−xSbO6:xFe3+ (S2−yCyS1−xS:xFe3+). Sr2ScSbO6:1%Fe3+ (SSS:1%Fe3+) phosphor shows broadband NIR emission at 904 nm and near‐unity IQE under excitation at 300 nm. Experimental and theoretical calculation results demonstrate that introduced Ca ions could increase the bandgap value and Debye temperature (ΘD) of host from Eg = 3.702 eV, ΘD = 609 K of y = 0 to Eg = 3.801 eV, ΘD = 692 K of y = 2. Significantly, the resultant S2−yCyS1−xS:1%Fe3+ NIR phosphors show wavelength‐tunable emission from 904 to 952 nm and high IQE of 84.6%–97.5% as well as enhanced thermal stability (I423K/I298K = 76.9%) of Ca2ScSbO6:1%Fe3+ (CSS:1%Fe3+) in comparison with that (I423K/I298K = 70.6%) of pristine sample. We fabricated an NIR light‐emitting diodes (LED) device by using CSS:1%Fe3+ NIR phosphors with ultraviolet LED chip and demonstrated its potential applications in anticounterfeiting, information encryption, and night vision. [ABSTRACT FROM AUTHOR]

While numerous approaches have been devised to optimize the luminescence properties of Eu2+-activated phosphors, the quest for a simple design strategy to achieve color-tunable Eu2+ emission remains a significant challenge. Here, we present a straightforward, doping-free method to tailor the site occupation of Eu2+ and modify its luminescence properties. In the pristine sample, the NaBaB9O15 (NBB) host featuring two cation sites (Na+ and Ba2+), Eu2+ exclusively occupies the Ba2+ site, resulting in blue emission when the NBB:Eu2+ phosphor is synthesized in a H2 reducing atmosphere. When we use CO instead of a H2 reducing atmosphere, impressively, the formation energy required for heterovalent substitution of Na+ by Eu2+ is lowered, leading to the emergence of a distinct green emission band. Significantly, the resultant phosphor NBB:Eu2+@CO exhibits not only a high internal quantum yield of 85.1% and zero-thermal-quenching behavior within the temperature range of 25–200 °C but also wavelength-tunable emission. Benefitting from the multi-color luminescence of the NBB:Eu2+@CO phosphor, its optical applications will no longer be confined to general lighting but extend to anti-counterfeiting and encryption. This study provides a novel design methodology for optimizing the optical properties of Eu2+-activated phosphors. [ABSTRACT FROM AUTHOR]

We have synthesized and investigated a series of yellow-emitting Sr3Ce(PO4)3:Eu2+ phosphors, showing an extreme broadband at around 535 nm (with a FWHM of ca. 200 nm/6760 cm−1) and a large Stoke shift (ca. 8265 cm−1), which is attributed to the 4f–5d transition of Eu2+ without the contribution from Ce3+ emission under excitation at long wavelengths (＞370 nm). However, such broadband Eu2+ emission is rather surprising, considering that there is only one cation site for the Eu2+ luminescent center. Herein, we investigated the crystal structure by performing X-ray Rietveld refinement on the synchrotron X-ray diffraction data, and demonstrate that both cation and anion sites in Sr3Ce(PO4)3 are disordered in the host lattice. These unusual structural characters generate a variety of distinct Eu2+ sites, which is verified by decay lifetime analysis and electron paramagnetic resonance spectra, and thus result in astonishing broadband yellow-emission. Moreover, a white LED device with a color-rendering index of 86.5, a color temperature of 5996 K, and chromaticity coordinates of (0.32, 0.38) was obtained by combining a 405 nm near-UV LED chip and the phosphor blends of yellow-emitting Sr3Ce(PO4)3:Eu2+ and the commercial blue-emitting BaMgA10O17:Eu2+ phosphor. These results indicate that the as-prepared yellow-emitting Sr3Ce(PO4)3:Eu2+ phosphor has potential applications in the dual-color-phosphor-converted WLEDs. [ABSTRACT FROM AUTHOR]