Near‐Infrared Light‐Emitting Diodes utilizing a Europium‐Activated Calcium Oxide Phosphor with External Quantum Efficiency of up to 54.7%

Abstract

Near‐infrared (NIR) luminescence materials with broadband emissions are necessary for the development of light‐emitting diodes (LEDs) based light sources. However, most known NIR‐emitting materials are limited by their low external quantum efficiency. This work demonstrates how the photoluminescence quantum efficiency of europium‐activated calcium oxide (CaO:Eu) NIR phosphor can be significantly improved and stabilized at operating temperatures of LEDs. A carbon paper wrapping technology is innovatively developed and used during the solid‐state sintering to promote the reduction of Eu3+ into Eu2+. In parallel, the oxygen vacancies in the CaO lattice are repaired utilizing GeO2 decomposition. Through this process, a record‐high external quantum efficiency of 54.7% at 740 nm is obtained with a thermal stability greatly improved from 57% to 90% at 125 °C. The as‐fabricated NIR‐LEDs reach record photoelectric efficiency (100 mA@23.4%) and output power (100 mA @ 319.5 mW). This discovery of high‐performance phosphors will open new research avenues for broadband NIR LED light sources in a variety of photonics applications.

Highly Efficient Broadband Near-Infrared Luminescence with Zero-Thermal-Quenching in Garnet Y3In2Ga3O12:Cr3+ Phosphors

“…The photoluminescence excitation and emission spectra of these compounds are plotted in Figure 1b,c, respectively. The excitation spectra present two intense bands with peaks located in blue and red regions, which can be assigned to 4 A 2 ( 4 F) → 4 T 1 ( 4 F) and 4 A 2 ( 4 F) → 4 T 2 ( 4 F) transitions of Cr 3+ , respectively. 42 Upon 450 nm excitation, a broadband NIR emission covering 700−1100 nm with emission peaks ranging from 730 to 830 nm can be observed in this family.…”

“…The DR spectra present two intense absorption bands with peaks located in blue (453 nm) and red (633 nm) regions, showing consistence with the excitation spectra monitored at 760 nm. These two peaks be assigned to 4 A 2 ( 4 F) → 4 T 1 ( 4 F) and 4 A 2 ( 4 F) → 4 T 2 ( 4 F) transitions of Cr 3+ , respectively. Upon 450 nm excitation, a broadband NIR emission covering 650−1100 nm with a peak wavelength of 760 nm (13,157 cm −1 ) and a FWHM of 125 nm (2135 cm −1 ) can be observed.…”

Modulation of Thermally Stable Photoluminescence in Cr3+-Based Near-Infrared Phosphors

“…19 CaO:Eu 2+ NIR phosphor (∼740 nm) with a record high external quantum efficiency (EQE) of 54.7% has been reported recently. 20 NIR emissions of Mn 2+ and Fe 3+ ions have been also reported in different systems, such as MgAl 2 O 4 :Mn 2+ (∼825 nm), Li 5 Zn 8 Al 5 Ge 9 O 36 :Mn 2+ (∼800 nm), Mg 2 GeO 4 : Mn 2+ (∼735 nm), SrAl 12 O 19 :Fe 3+ (∼810 nm), and Li-GaO 2 :Fe 3+ (∼748 nm). 21−25 Ni 2+ and Bi ion-activated glass materials exhibit ultrabroadband optical radiation in 800−1700 nm.…”

“…As the most promising substitute for thermal radiation lamps, extensive efforts have been made to exploit broadband NIR phosphors via Eu 2+ , Cr 3+ , Ni 2+ , Mn 2+ , Fe 3+ , or Bi 3+ ion-activated inorganic matrices. , For example, giant red-shifted emissions from red to NIR (620 to 773 nm) are realized via a 450 nm blue LED and coated (Sr,Ba)­Y 2 O 4 :Eu 2+ phosphors . CaO:Eu 2+ NIR phosphor (∼740 nm) with a record high external quantum efficiency (EQE) of 54.7% has been reported recently . NIR emissions of Mn 2+ and Fe 3+ ions have been also reported in different systems, such as MgAl 2 O 4 :Mn 2+ (∼825 nm), Li 5 Zn 8 Al 5 Ge 9 O 36 :Mn 2+ (∼800 nm), Mg 2 GeO 4 : Mn 2+ (∼735 nm), SrAl 12 O 19 :Fe 3+ (∼810 nm), and LiGaO 2 :Fe 3+ (∼748 nm). − Ni 2+ and Bi ion-activated glass materials exhibit ultrabroadband optical radiation in 800–1700 nm. , Among these abundant activators, the NIR emission of Eu 2+ ions hardly shifted to the longer wavelength region (after 800 nm) until now, and the NIR luminescence efficiency of Mn 2+ , Fe 3+ , Ni 2+ , and Bi 3+ ions is unsatisfactory .…”

Efficient broadband near-infrared emission induced by Nb5+ substitution for Ta5+ in GaTa1−yNbyO4:Cr3+ phosphor

“…[8][9][10][11] The Bi 3+/2+/+ , Eu 2+ , Ce 3+ , and Mn 5+/4+/2+ activators have emission wavelengths close to that of deep red light which makes their applications in the NIR region limited. [12][13][14][15][16] Furthermore, although there has been significant progress in recent years in research around Sb 3+ -doped NIR phosphors, 17,18 their quantum efficiency is low and the preparation process is relatively complex. The transition metal Cr 3+ exhibits broadband emission in the 650-1300 nm range originating from the 3d-3d transition when Cr 3+ is located in a weak octahedral coordination environment.…”