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273 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on K3CrC5N6O by Materials Project

CrK6CrC10(N6O)2 crystallizes in the orthorhombic Pnc2 space group. The structure is three-dimensional and consists of two chromium molecules and one K6CrC10(N6O)2 framework. In the K6CrC10(N6O)2 framework, there are four inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in an octahedral geometry to four N3- and two equivalent O2- atoms. All K–N bond lengths are 3.10 Å. Both K–O bond lengths are 2.90 Å. In the second K1+ site, K1+ is bonded in a 6-coordinate geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.87–3.27 Å. In the third K1+ site, K1+ is bonded in a distorted octahedral geometry to six N3- atoms. There are a spread of K–N bond distances ranging from 2.78–3.15 Å. In the fourth K1+ site, K1+ is bonded in a 4-coordinate geometry to four N3- and two equivalent O2- atoms. There are a spread of K–N bond distances ranging from 2.85–3.24 Å. There are one shorter (3.01 Å) and one longer (3.02 Å) K–O bond lengths. Cr3+ is bonded in a linear geometry to two equivalent N3- atoms. Both Cr–N bond lengths are 1.83 Å. There are five inequivalent C+2.80+ sites. In the first C+2.80+ site, C+2.80+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.17 Å. In the second C+2.80+ site, C+2.80+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.18 Å. In the third C+2.80+ site, C+2.80+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.18 Å. In the fourth C+2.80+ site, C+2.80+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.17 Å. In the fifth C+2.80+ site, C+2.80+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.17 Å. There are six inequivalent N3- sites. In the first N3- site, N3- is bonded in a 1-coordinate geometry to three K1+ and one C+2.80+ atom. In the second N3- site, N3- is bonded in a linear geometry to one Cr3+ and one O2- atom. The N–O bond length is 1.23 Å. In the third N3- site, N3- is bonded in a 1-coordinate geometry to three K1+ and one C+2.80+ atom. In the fourth N3- site, N3- is bonded in a 4-coordinate geometry to three K1+ and one C+2.80+ atom. In the fifth N3- site, N3- is bonded in a distorted single-bond geometry to three K1+ and one C+2.80+ atom. In the sixth N3- site, N3- is bonded in a distorted single-bond geometry to three K1+ and one C+2.80+ atom. O2- is bonded to three K1+ and one N3- atom to form distorted corner-sharing OK3N tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Heterovalent Substitution of K 2 SrP 2 O 7 :Cr 3+ to Achieve Anti-Thermal-Quenching Broadband Near-Infrared Luminescence

Broadband near-infrared (NIR) light sources based on phosphor-converted light-emitting diodes are highly desirable for biochemical analysis and medical diagnosis applications. However, thermal quenching remains a demanding challenge for developing efficient NIR phosphors. Herein, we report the enhancement of both quantum efficiency and thermal stability in Cr 3+ -activated K 2 SrP 2 O 7 phosphors through a heterovalent substitution strategy by replacing Sr 2+ with Al 3+ in K 2 Sr 1–x Al x P 2 O 7 (0.05 ≤ x ≤ 0.2) to obtain optimized broadband NIR emission. Structural modulation via Al 3+ substitution leads to the optimized composition, K 2 Sr 0.88 Al 0.1 P 2 O 7 :0.02Cr 3+ , which emits across a broad NIR range of 650–1100 nm peaking at 807 nm with a full width at half-maximum of ∼130 nm under 448 nm excitation. Remarkably, its emission intensity at 150 °C remains 120% of the initial value at room temperature, demonstrating a rare antithermal-quenching behavior. Temperature-dependent XRD studies further reveal that Al 3+ substitution effectively suppresses lattice expansion at elevated temperatures, indicating enhanced lattice stability under thermal excitation. Detailed structural and spectral analyses show that the substitution enhances local site symmetry, reduces electron–phonon coupling, increases thermally induced absorption probability, and fortifies energetic barriers against nonradiative transitions. These synergistic effects collectively endow this NIR phosphor with a superior thermal stability. Furthermore, NIR light-emitting diodes fabricated with this phosphor exhibit strong potential for applications in information identification, nondestructive detection, and night vision technologies. This study demonstrates a local structure engineering strategy for designing thermally robust Cr 3+ -activated NIR phosphors, offering valuable insights into material discovery and NIR spectroscopy device development.

Cr3+↗
DOE OSTI2025

High-pressure Cr 3+ luminescence and Raman spectroscopy of a natural MgAl 2 O 4 spinel to ∼60 GPa

Cr 3+ luminescence and Raman spectroscopy of a natural spinel were collected up to ∼60 GPa at ambient temperature using a Ne or a 4:1 methanol-ethanol mixture as the pressure transmitting media. Here, in the Ne experiments above ∼40 GPa, and in the 4:1 methanol–ethanol experiments above ∼20 GPa, all luminescence emission lines shift non-linearly, and by 59 GPa the spectra are broadened and are significantly changed. The Raman modes shift smoothly to higher frequencies with pressure, with a slight change in slope above 40 GPa, with no kinks or discontinuities. By ∼60 GPa, only the most intense Eg mode remains resolvable, appearing broadened and reduced in intensity. The change in slope in the Raman modes and luminescence bands may be due to a change in the compression mechanism of spinel. When spinel was decompressed from 40 GPa all changes were fully reversible; however, when the samples were decompressed from 54 to 60 GPa in Ne and 59 GPa in 4:1 methanol-ethanol the spectra were irreversibly changed. The change in the luminescence spectra and the Raman spectra are likely due to a pressure induced disorder of the anions or partial amorphization between 40 and 60 GPa.

Cr3+↗