Ultra‐Wide Vis–NIR Mg₂Al₄Si₅O₁₈:Eu²⁺,Cr³⁺ Phosphor Containing Unusual NIR Luminescence Induced by Cr³⁺ Occupying Tetrahedral Coordination for Hyperspectral Imaging

Abstract

sources represented by halogen lamps, such as high energy consumption, short lifetime, and large heat release, and show huge application potential in agriculture, food, and bioimaging fields. [1] The pivotal long-wavelength Cr 3+ -activated NIR phosphors for NIR pc-LEDs are heavily dependent on expensive Sc-and In-based compounds. [2] LiScGeO 4 is a typically long-wavelength NIR phosphor with peak wavelength of 1120 nm and full-width at half-maximum (FWHM) of 300 nm. [3] The fabricated NIR pc-LED can check the file level of opaque items due to its high penetrating power ability. The emission peak is turned from 970 to 1020 nm, and FWHMs are broadened from 225 to 285 nm in (Li,Na)In 2 SbO 6 :Cr 3+ by substituting Li + with Na + , the NIR pc-LED has the merit of avoiding red storms. [4] Unfortunately, the low thermal stability and high cost are a brake on the practical application. Simultaneously, the characteristics of Cr 3+ -doped NIR phosphor in UV and visible (Vis) light absorption bands make it impossible to realize short-wavelength emission, neglecting the demand of ultra-wide Vis-NIR luminescent materials for nondestructive Cr 3+ -activated broadband near-infrared (NIR) phosphors, featured by the octahedral coordination preference and strong absorption in visible (Vis) region, have great potential application in nondestructive assessment. It is still a challenge to develop Cr 3+ -doped phosphors with the tetrahedrally coordinated Cr 3+ NIR emission behavior and ultra-wide Vis-NIR luminescence.

Cr3+-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs

“…The D r values of Cr 3+ substitutes Al 3+ and Sb 5+ are both below 15%. According to previous reports, Cr 3+ prefers to occupy the octahedral coordination . Therefore, Cr 3+ tends to replace the Al 3+ and Sb 5+ lattice sites.…”

“…According to previous reports, Cr 3+ prefers to occupy the octahedral coordination. 26 Therefore, Cr 3+ tends to replace the Al 3+ and Sb 5+ lattice sites. When Cr 3+ replaces Sb 5+ , its possible charge compensation mechanism is provided by the oxygen vacancy, Sb 5+ + O 2− → Cr 3+ + vacancy (O 2− ).…”

An efficient and thermally stable Cr3+-activated Y2GdSc2Al2GaO12 garnet phosphor for NIR spectroscopy applications

“…As previously reported, Cr 3+ ions tend to occupy an octahedral coordination position. 34 Besides, considering the similar effective ionic radii of Sc 3+ ( r = 0.745 Å, coordination number (CN) = 6) and Cr 3+ ( r = 0.615 Å, CN = 6) as well as the same valence state between them, the Cr 3+ will occupy the Sc 3+ site with charge balance. The SEM along with EDS element mapping images of the YGSAG:0.08Cr 3+ sample are displayed in Fig.…”

Near-infrared Sr7NaGa(PO4)6:Cr3+,Ln3+ (Ln = Nd, Er, and Yb) phosphors with different energy transfer paths: photoluminescence enhancement and versatility

“…25 However, the 3d electrons of Cr 3+ ions tend to couple to host lattices leading to a non-radiative transition, which has a negative effect on the luminescence properties of Cr 3+ doped NIR phosphors. 26–28…”