Highly Efficient and Stable Near‐Infrared Broadband Garnet Phosphor for Multifunctional Phosphor‐Converted Light‐Emitting Diodes

Abstract

light in this range is known as the first biological window, and the NIR radiation can effectively penetrate biological tissues, which means that a non-destructive and non-invasive diagnosis of the human physiological state can be performed by a perceptible penetration depth in biological tissues. [6] For plant cultivation, red/ photosensitive pigments (PR) and far-red/ photo sensitive pigments (PFR), two pigments indispensable for plant growth, have a specific absorption in the NIR region, and PFR has a strong absorption peak at 730 nm. [7] Various NIR-emitting materials have been developed for halogen lamps, lightemitting diodes (LEDs), organic LEDs (OLED), and phosphor-converted LEDs (pc-LEDs). Among them, halogen lamps have continuous ultra-broadband spectral properties from visible to NIR, but their low luminous efficiency, high operating temperature, and long response time limit their applications. [8] NIR LEDs overcome most of the drawbacks of halogen lamps, but the narrow fullwidth at half maximum (FWHM) and the LED arrangement luminous unevenness also severely limit their utilization at scale. [9] OLEDs are disappointing in terms of efficiency or temperature resistance, even though they have good applicability. [10] The most suitable solution may be the development of NIR pc-LEDs combining InGaN blue LED chips with broadband NIR phosphors. It satisfies both the ultra-broadband spectral emission and the requirements of compactness, efficiency, portability, and low cost. [11] For this purpose, broadband NIR phosphors that are well matched to the blue LED chips need to be developed.Many NIR broadband phosphors based on inorganic matrixdoped activators have been reported so far, [12] however, most of them have disadvantages such as unsuitable NIR emission wavelength, unstable emission intensity at high temperature, and low luminescence efficiency, which greatly limit their applications in various fields. Cr 3+ ions exhibit broadband absorption in the ultraviolet-visible spectral range, which stems from its unique 3d 3 electronic structure. [13] In addition, Cr 3+ ions can display tunable narrowband or broadband spectrum from 600-1600 nm, depending on whether they are in a strong or weak Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LED) are ideal light sources to meet the next generation of NIR spectroscopy. However, NIR phosphors have numerous problems such as low quantum yields (QY) and low thermal stability. In this work, a series of Gd 3 Y x In x Ga 5-2x O 12 :Cr 3+ NIR broadband phosphors with high internal quantum yields (IQYs) and high thermal stability are discovered by uniquely replacing GaO 6 in Gd 3 Ga 5 O 12 with Y 3+ and In 3+ in a co-doped manner through cation modulation. Under 449 nm excitation, Gd 3 Y 0.5 In 0.5 Ga 4 O 12 (GYIG):yCr 3+ depicts emission from 650 to 1050 nm with a full-width at half maximum (FWHM) of 134 nm. The emission intensity reaches its optimum value at y = 6%, while the IQY reaches an impressive 81.8% and, at 375 K, the emission intensity r...

Rapid Discovery of Efficient Long-Wavelength Emission Garnet:Cr NIR Phosphors via Multi-Objective Optimization

“…IQE/EQE values of published Cr 3+ -doped garnet NIR materials with different emission wavelengths. (1) Y 3 Al 5 O 12 :Cr, (2) Lu 3 Ga 5 O 12 :Cr, (3) Y 3 Ga 5 O 12 :Cr, (4) Gd 3 Ga 5 O 12 :Cr, (5) Lu 3 Sc 2 Ga 3 O 12 :Cr, (6) Gd 2.4 Lu 0.6 Ga 4 AlO 12 :Cr, (7) Gd 3 Al 2 Ga 3 O 12 :Cr, (8) Y 3 Sc 2 Ga 3 O 12 :Cr, (9) Y 2 CaAl 4 SiO 12 :Cr, (10) CaLu 2 Mg 2 Si 3 O 12 :Cr, (11) Ca 3 Ga 2 Ge 3 O 12 :Cr, (12) Gd 3 Sc 2 Ga 3 O 12 :Cr, (13) Gd 3 Sc 1.5 Al 0.5 Ga 3 O 12 :Cr, (14) Gd 3 Y 0.5 In 0.5 Ga 4 O 12 :Cr, (15) Gd 3 Mg 0.5 Al 1.5 Ga 2.5 Ge 0.5 O 12 :Cr (this work), (16) Ca 3 Sc 2 Si 3 O 12 :Cr, (17) Ca 2 YHf 2 Al 3 O 12 :Cr, (18) Ca 2 LuZr 2 Al 3 O 12 :Cr, (19) Sr 3 Y 2 Ge 3 O 12 :Cr, (20) Ca 3 Y 2 Ge 3 O 12 :Cr, (21) Gd 3 Zn 0.8 Ga 3.4 Ge 0.8 O 12 :Cr, (22) La 3 Sc 2 Ga 3 O 12 :Cr, (23) Ca2LaZr 2 Ga 2.8 Al 0.2 O 12 :Cr, (24) Gd 3 MgScGa 2 SiO 12 :Cr, (25) Ca 4 ZrGe 3 O 12 :Cr …”

Producing Tunable Broadband Near-Infrared Emission through Co-Substitution in (Ga1–xMgx)(Ga1–xGex)O3:Cr3+

“…Generally, there are two considerations for red-shifting the emission spectrum of Cr 3+ -activated materials. One involves the coupling of Cr 3+ -Cr 3+ ion pairs, which will induce significant energy level splitting due to the strong exchange interactions between Cr 3+ -Cr 3+ , whereas the other is through the weakening of the crystal field environment. − The EPR spectrum does not support the presence of Cr 3+ -Cr 3+ ion pairs, and the nearly unchanged absorption (DR and excitation peaks) indicates an essentially constant crystal field environment. Thus, the red-shift caused by [Mg 2+ -Ge 4+ ] co-substitution must follow a different mechanism.…”

Mn ions‐activated Gd3(Al,Ga)5O12 garnet solid‐solution ceramics: Cation substitution for dual wavelength red‐emission

“…Moreover, the Raman peak in middle‐frequency range 300–450 cm −1 , which corresponds to the octahedral Al/Ga/MnO 6 , became wider as increasing Ga 3+ content. This is because the incorporation of Ga 3+ results in the volume of Al/GaO 6 to expand and its local symmetry to change 35 . The vibrational peak in the high‐frequency range (700–800 cm −1 ) dominated by Al/GaO 4 gradually shifted to the low‐frequency range with the increase of Ga 3+ addition.…”

“…This is because the incorporation of Ga 3+ results in the volume of Al/GaO 6 to expand and its local symmetry to change. 35 The vibrational peak in the high-frequency range (700-800 cm −1 ) dominated by Al/GaO 4 gradually shifted to the low-frequency range with the increase of Ga 3+ addition. Appearance and in-line transmittance spectra of GAGG:Mn SSCs with different Al/Ga ratios are shown in Figure 5B.…”