Developing Broadband Cr³⁺-Substituted Phosphor-Converted Near-Infrared Light Sources

Abstract

Near-infrared (NIR) spectroscopy is a rapidly growing research area due to its noninvasive, inexpensive, and rapid analysis capabilities spanning various applications. The key technology behind the growth of this field involves phosphor-converted NIR light-emitting diodes (pc-NIR LEDs) due to their energy efficiency, long operating lifetimes, and chemical and physical stability. Numerous studies have reported new Cr3+-substituted phosphors that can more effectively convert blue LED emission to NIR radiation with a broad full-width-at-half-maximum (fwhm) that covers a significant portion of the interatomic vibrational spectrum. However, there is still much to learn about these materials’ structure–property relationships. In this Spotlight on Applications, we discuss current research progress in designing broadband Cr3+ phosphors as sources of NIR light, specifically emphasizing our research. We examine results from our work and others that have been used to create an efficient broadband emission in the NIR range. The discussion also emphasizes various techniques to analyze and improve temperature-dependent photoluminescence. Finally, we highlight the potential applications of Cr3+-based pc-NIR LEDs in fields such as night vision, bioimaging, and food freshness and analysis. This Spotlight on Applications aims to provide an overview of the progress of pc-NIR LEDs based on Cr3+ by emphasizing the challenges associated with its advancement while offering a few suggestions for ventures in this field.

A novel broadband Ba3Ca4(BO3)3(SiO4)Cl:Mn4+ near-infrared phosphor with a special pseudo-octahedral Mn4+ coordination structure

“…Accordingly, the range of emission wavelengths is also increased from a narrowband (700–900 nm at 100 K) to a broadband (650–1200 nm at 425 K). The temperature-dependent FWHM can be used to evaluate the strength of electron–phonon coupling by calculating the Huang–Rhys parameter ( S ) as follows: 44 where ω represents the phonon frequency, and k is the Boltzmann constant. According to Wang et al 's research, the above equation can be approximated as: 45 FWHM 2 = a + b ×2 kT where a = 5.57 S ( ħω ) 2 , and b = 5.57 Sħω .…”

“…Hence, the inhomogeneous broadening of the BCBSC:0.01Mn 4+ emission band is attributed to the enhancement of electron–phonon coupling with the increase of temperature. 44–47…”

Advancing Reporting Guidelines for Optimal Characterization of Inorganic Phosphors

“…The preparation and identification of phosphor materials in the single-crystalline phase are crucial due to the direct impact of crystallographic features on the resulting optical properties. For example, Eu 2+ -based narrowband red phosphors benefit from a crystalline host system with cuboid coordination, while Cr 3+ -based broadband near-infrared phosphors require multisite crystallographic environments . X-ray diffraction, using the Rietveld refinement strategy, is a powerful tool for phase identification and obtaining crystallographic details.…”

“…In contrast, Eu 3+ emission exhibits sharp red lines and is considered less attractive in this context. Similarly, Cr 3+ emits near-infrared light, while Cr 4+ emits shortwave infrared light. , XAS and XPS are valuable techniques in X-ray spectroscopy, but they have distinct characteristics. XAS provides information about the average electronic structure of a material with limited depth sensitivity, while XPS is surface-sensitive, typically probing within a few nanometers.…”

Non-destructive food-quality analysis using near-infrared luminescence from Mg3Gd2Ge3O12:Cr3+

“…while maintaining a high photoluminescence quantum yield (PLQY) within the NIR region. 18 As a result, numerous Cr 3+ -substituted luminescent materials have been reported. 6,16,19–27 Research has focused specifically on identifying ways to achieving broadband Cr 3+ NIR luminescence with nearly optimal PLQY values and robust optical properties as a function of temperature, which is determined based on the remaining emission intensity at 423 K ( I 423K ), an LED's approximate upper operating temperature.…”