Infrared to Short-Wave Infrared-Emitting Phosphors for Light-Emitting Diode Applications

Abstract

In the past decade, near-infrared (NIR) materials have been developed for sensor applications. NIR light-emitting diodes (LEDs) facilitate roadside high-accuracy light detection and ranging, thus enhancing driver safety and confidence. With advancements in wearable technology, individuals, particularly young people, have exhibited a desire to track their own health. Thus, nonintrusive light detection is likely to become the mainstream of detection technology. However, short-wave infrared (SWIR) phosphors are still under development. In the present study, we explored materials with the potential for NIR to SWIR emission, such as Eu2+ (ultrahigh crystal field), Cr3+ (six-fold coordination), and Ni2+ (six-fold coordination) activators. Ni2+ is a suitable SWIR activator; however, its blue light (450 nm) absorption ability is weak. The high-efficiency transfer of energy from Eu2+ and Cr3+ to Ni2+ opens a new avenue for research on SWIR phosphors. We further sorted the materials with high potentials for bioimaging and image recognition applications. SWIR light can penetrate deep into biological tissues and be used to observe the characteristic absorption frequencies of various functional groups. Therefore, SWIR light is used in wearable technology, clinical diagnosis, and chair-side dental checkup. With the help of the artificial intelligence of things technology, image recognition facilitates fast and nondestructive detection. In the future, SWIR phosphors, which help avoid high temperature and working noise, may replace traditional halogen lamps. Our findings reveal the key factors influencing SWIR phosphors and provide insights into the application design. The tunable emission of SWIR phosphors in the 1000–1700 nm spectral range facilitates their widespread applications.

Sharp-to-Broad Band Energy Transfer in Lithium Aluminate and Gallate Phosphors for SWIR LED

“…This observation is attributed to molecular vibrations in the silicon package gel, where fundamental absorptions occur ranging from the first to the third overtone, per the harmonic approximation. These absorption dips are particularly noticeable in hydrogen-based bonds such as C–H, O–H, and N–H . These bonds exhibit higher vibrational energies in the SWIR region, encompassing stretching and bending modes.…”

“…These absorption dips are particularly noticeable in hydrogen-based bonds such as C−H, O−H, and N−H. 36 These bonds exhibit higher vibrational energies in the SWIR region, encompassing stretching and bending modes. Specifically, the second overtones of functional groups such as CH 3 −, CH 2 −, and CH− exhibit absorption in the 1100−1200 nm range, and ArOH exhibits absorption in the 1200−1300 nm range.…”

Plastic Identification by Using Energy Transfer Enhanced Broadband Short-Wave Infrared Phosphor Mg3Ga2GeO8:Cr3+, Ni2+

“…Short-wave infrared (SWIR) light, with an emission range of 1,100–1,700 nm, belongs to near-infrared (NIR) light. SWIR light has drawn lots of attention owing to its advantages of high penetration and even can penetrate through biological tissues innocuously. − In recent years, numerous applications have derived from NIR light with an emission range of 700–1,000 nm to SWIR light, starting from basic night vision technology to biomedical imaging applications, and recently, it has even been able to be a great light source of artificial intelligence image recognition system to improve its accuracy . Nowadays, it has been a trend that NIR emission phosphor material combines with light emitting diodes (LEDs) because of its advantages of being inexpensive, highly efficient, and compact, which are the reasons for its suitability as reliable light sources.…”

Hidden Hexavalent Chromium Ions with Subtle Structural Evolution in Near-Infrared Phosphors

“…The transition between the 4 T 2 to 4 A 2 (transition allowed) and 2 E to 4 A 2 (transition forbidden) energy levels of Cr 3+ ions enables an efficient broadband emission around 800–1000 and a 700 nm narrowband emission, respectively . Previous studies have investigated several Cr 3+ -doped NIR phosphors, such as La 3 Ga 5 GeO 14 :Cr 3+ (garnet-type), ZnGa 2 O 4 :Cr 3+ (spinel-type), Mg 2 InSbO 6 :Cr 3+ (perovskite-type), and Sr 9 Sc­(PO 4 ) 7 (whitlockite-type). − These materials exhibit promising luminescent properties and have been extensively studied for their potential applications in different technological fields. − In all NIR phosphor structures, six-coordination sites within a crystal lattice play a crucial role in modulating its luminescent properties. When Cr 3+ ions occupy six-coordination sites, such as octahedral or distorted octahedral environments, it affects the crystal field splitting and energy levels of the electronic orbitals. − …”