Broadband infrared LEDs based on europium-to-terbium charge transfer luminescence

Abstract

Efficient broadband infrared (IR) light-emitting diodes (LEDs) are needed for emerging applications that exploit near-IR spectroscopy, ranging from hand-held electronics to medicine. Here we report broadband IR luminescence, cooperatively originating from Eu 2+ and Tb 3+ dopants in CaS. This peculiar emission overlaps with the red Eu 2+ emission, ranges up to 1200 nm (full-width-at-half-maximum of 195 nm) and is efficiently excited with visible light. Experimental evidence for metal-to-metal charge transfer (MMCT) luminescence is collected, comprising data from luminescence spectroscopy, microscopy and X-ray spectroscopy. State-of-the-art multiconfigurational ab initio calculations attribute the IR emission to the radiative decay of a metastable MMCT state of a Eu 2+ -Tb 3+ pair. The calculations explain why no MMCT emission is found in the similar compound SrS:Eu,Tb and are used to anticipate how to fine-tune the characteristics of the MMCT luminescence. Finally, a near-IR LED for versatile spectroscopic use is manufactured based on the MMCT emission.

Recent Advances in 2D Rare Earth Materials

“…Under external stimulation, the electrons of materials will be transferred from excited state to ground state and then luminescence comes out. [125][126][127] For luminescent semiconductors, the radiative recombination of excitons and Coulomb-bound electron-hole pair states produces luminescence. [128][129][130][131][132] And the electronic band structures determine the final luminescent wavelength.…”

Cr3+‐Doped Sc‐Based Fluoride Enabling Highly Efficient Near Infrared Luminescence: A Case Study of K2NaScF6:Cr3+

“…[ 1–7 ] In particular, since the biological tissues are transparent for the NIR light in some degree, radioistopes‐free tissue imaging, noninvasive tissue analyzing during biopsy or endoscopy, and infrared (IR) therapy can be constructed. [ 8 ] The traditional tungsten filament, halogen lamps, and supercontinuum lasers can generate broadband NIR emission, but showing large sizes, incompactness, and low energy efficiency as well, the applications are limited. Though the AlGaAs NIR light‐emitting diodes (LEDs) possess the advantages of small size, high efficiency, and long lifetime, their full width at half maximum (FWHM < 50 nm) is too narrow.…”

“…Currently, the broadband NIR emission was mainly obtained in rare‐earth ion Eu 2+ or transition metal ion Cr 3+ (or Mn 2+ ) into some suitable structures. [ 8,14–16 ] Especially, the Cr 3+ with an unique 3d 3 electron configuration, it is easy to generate broadband NIR luminescence by doping Cr 3+ into a weak octahedral crystal field environment. Guided by this design principle, a considerable number of Cr 3+ ‐doped broadband NIR‐emitting phosphors for pc‐LEDs have been explored, such as ScBO 3 :Cr 3+ (FWHM = 120 nm, λ em = 800 nm), [ 17 ] La 2 MgZrO 6 :Cr 3+ (FWHM = 210 nm, λ em = 825 nm), [ 18 ] La 3 Ga 5 GeO 14 :Cr 3+ (FWHM = 330 nm, λ em = 750 nm), [ 16 ] NaScGe 2 O 6 :Cr 3+ (FWHM = 140 nm, λ em = 840 nm), [ 19 ] LiInSi 2 O 6 :Cr 3+ (FWHM = 143 nm, λ em = 840 nm), [ 20 ] LiScP 2 O 7 :Cr 3+ (FWHM = 170 nm, λ em = 880 nm), [ 21 ] Ca 3 Sc 2 Si 3 O 12 :Cr 3+ (FWHM = 92 nm, λ em = 783 nm), [ 22 ] Ca 2 LuZr 2 Al 3 O 12 :Cr 3+ (FWHM = 145 nm, λ em = 785 nm), [ 23 ] and Gd 3 Sc 2 Ga 3 O 12 :Cr 3+ (FWHM = 120 nm, λ em = 756 nm).…”

Efficient red and broadband near‐infrared luminescence in Mn2+/Yb3+‐doped phosphate phosphor

“…In addition to the urgent need for red‐emitting materials, NIR emission materials for NIR pc‐LED are also in great demand because of their widely applications in optical communication, night‐vision technologies, bioimaging, food analysis, medical fields, etc 34‐41 . The nature of the narrow excitation and emission bands of NIR emitters doped with trivalent rare‐earth ions limits their applications in NIR pc‐LED 42,43 .…”

“…communication, night-vision technologies, bioimaging, food analysis, medical fields, etc. [34][35][36][37][38][39][40][41] The nature of the narrow excitation and emission bands of NIR emitters doped with trivalent rare-earth ions limits their applications in NIR pc-LED. 42,43 Therefore, it is urgent to find NIR materials with broad excitation and emission bands.…”