Honghong Lei,Peng Jiang,Bin Li,Yuncheng Zhou,Rui Zhang,Jianlei Kuang,Wenbin Cao,Wei Wang
The (S, N) co-doped Ba 2 In 2- x Cr x O 5+ y (0 ≤ x ≤ 0.5) oxides are successfully obtained by mixing the Ba 2 In 2- x Cr x O 5+ y oxides and thiourea through a simple ball milling method followed by sintering at 400 °C for 3 h. The colors of the compounds change from orange-brown to yellow-green after reacting with thiourea. When Cr amount is small ( x = 0.1), the crystal structure of (S, N) co-doped Ba 2 In 2- x Cr x O 5+ y is orthorhombic Ba 2 In 2 O 5 phase. When x ≥ 0.3, the crystal structure of the sample is cubic BaInO 2.5 phase. And this phase transition is the same as Ba 2 In 2- x Cr x O 5+ y . XPS results reveal that Cr 6+ in Ba 2 In 2- x Cr x O 5+ y (0 ≤ x ≤ 0.5) oxides are reduced to Cr 3+ after sintering. S exists in both cation and anion forms, and N exists in substitutional forms. UV–Vis analysis indicates that the yellow-green hue comes from the d-d transition of Cr 3+ , and the doping of S, N ions leads to a red shift of the absorption edge of the samples.
Near-infrared (NIR) phosphor-converted (pc) light-emitting diodes (LEDs) are gaining popularity as smart NIR spectroscopy light sources. However, the low wall-plug efficiency (WPE) of NIR pc-LEDs has limited their applications due to the comprehensive properties of external quantum efficiencies (EQEs) and thermal stability for NIR phosphors. In this study, a simple strategy is presented to achieve high-performance NIR phosphors by breaking the d–d parity forbidden transitions of Cr 3+ in the garnet host by introducing asymmetric vibrations via lattice distortions. The achieved EQE is as high as 44% at room temperature and maintains >98% of the initial EQE at 150 °C, demonstrating excellent thermal stability. Notably, these NIR phosphors enable unprecedented NIR pc-LEDs with a record WPE of 26% driven at 100 mA. Consequently, the application of NIR pc-LEDs is expanded to new areas such as real-time heart rate monitoring and fingerprint recognition.
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