Efficient Ultra‐Broadband Ga₄GeO₈:Cr³⁺ Phosphors with Tunable Peak Wavelengths from 835 to 980 nm for NIR pc‐LED Application

Abstract

Near‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) hold great potential for applications ranging from night vision to non‐destructive detection. However, it remains a long‐standing challenge to develop NIR phosphors simultaneously with longer‐wavelength broadband emissions and higher efficiency. Herein, ultra‐broadband Ga4GeO8:Cr3+ (GGO:Cr3+) phosphors are developed, with the NIR emission covering 700–1300 nm. Furthermore, tunable emission bands peaking from 835 to 980 nm are achieved simply by varying the Cr3+ concentration. Particularly, emission maxima (λmax) of GGO:xCr3+ shift from 850 to 900 nm without intensity loss when increasing x values between 0.02 and 0.10. An internal quantum yield of 60% is achieved for GGO:0.02Cr3+ (λmax ≈ 850 nm, full width at half maximum (FWHM) ≈215 nm). The origin of tunable ultra‐broadband emissions of GGO:Cr3+ is revealed on the basis of structural and time‐resolved spectroscopic analysis. The pc‐LED fabricated by GGO:0.02Cr3+ exhibits a maximum NIR output power of ≈56 mW at 400 mA drive current, and its application in high‐penetration quality analysis of fruits is also demonstrated. The results indicate that GGO:Cr3+ phosphors have high promise for practical applications in NIR pc‐LED devices.

Recent Advances in Chromium‐Doped Near‐Infrared Luminescent Materials: Fundamentals, Optimization Strategies, and Applications

“…Ga 4 GeO 8 :Cr 3+ developed by Shao et al also shows an ultrabroadband NIR emission (700-1300 nm, FWHM ≈ 215 nm). [34] The luminescence of Ga 4 GeO 8 :Cr 3+ covers the similar spectral range as La 3 Ga 5 GeO 14 :Cr 3+ and much stronger at longer wavelengths (>850 nm) (Figure 3b). Moreover, the NIR luminescence of Ga 4 GeO 8 :Cr 3+ shows a dramatic red-shift (835-980 nm) via varying the Cr 3+ concentration based on the existence of multiple Cr 3+ -emitting centers.…”

Enhanced Thermal Stability and Energy Transfer by Crystal‐Field Engineering in a Garnet Phosphor for Thermometry and NIR‐LED

“…[15b,27] The absorption of NIR light from organic matter in the 700-2500 nm wavelength band is mainly the frequency doubling and frequency combining absorption of hydrogen-containing groups (-OH, -CH, -NH, -SH). [28] Most of the organic compounds in meat (such as proteins, fats, organic acids, carbohydrates) contain different hydrogen-containing groups. Because different types and quantities of the hydrogencontaining groups will lead to different absorptions of NIR light, [21] the ratio of the intensity of the different emission peaks can be used to distinguish meats.…”

Thermally stable and tunable broadband near-infrared emission from NIR-I to NIR-II in Bi-doped germanate glass for smart light sources

“…Cr 3+ ions within phosphors have been proven to be favorable NIR active centers and have shown their superiority to other activator ions in emission bandwidth (>150 nm), high internal quantum efficiency (IQE > 90%), and effective blue light excitation. 18–23 However, the spectral region of Cr 3+ usually covers only the NIR I region (650–1000 nm), and it is still difficult to tune the emission peak of Cr 3+ beyond 1000 nm or longer in the NIR II region (1000–1700 nm). Light from the NIR-II region is more conducive to biological detection and imaging, real-time and nondestructive inspection due to its lower scattering and deeper penetration in biological tissues, and providing more information on relevant functional groups (such as O–H, C–H, and N–H bonds).…”