Abstract:Broadband near‐infrared (NIR) phosphor‐converted light emitting diode (pc‐LED) is demanded for wearable biosensing devices, but it suffers from low efficiency and low radiance. This study reports a broadband NIR Ca3‐xLuxHf2Al2+xSi1−xO12:Cr3+ garnet phosphor with emission intensity enhanced by 81.5 times. Chemical unit co‐substitution of [Lu3+−Al3+] for [Ca2+−Si4+] is responsible for the luminescence enhancement and further alters the crystal structure and electronic properties of the garnet. Using the optimize… Show more
“…The total radiant flux of the IR part of the emission amounts to 38 mW. This value surpasses the current Cr 3+ -based state-of-the-art, having IR radiant fluxes in the range of 20–25 mW 4 – 6 , 8 – 10 , by 50%. Fig.…”
Section: Resultsmentioning
confidence: 76%
“…The broadband IR MMCT emission is now applied to construct an IR pc-LED that can directly be used for the numerous above-mentioned spectroscopic applications. Because of the high absorption strength of the parity-allowed 4 f −5 d transitions of Eu 2+ , higher external quantum efficiencies can be achieved than with the current state-of-the-art, Cr 3+ -based phosphors 4 – 6 , 8 – 10 . Furthermore, the extremely broad MMCT emission extends the covered spectral range by several hundreds of nanometers to the IR compared to red/near-IR single Eu 2+ 5 d −4 f emission 11 .…”
Section: Resultsmentioning
confidence: 99%
“…A large market that is presently explored is IR LEDs for the use in smart devices (e.g., mobile phones) to analyze food: information about its freshness, caloric value, or allergen content can be derived from the built-in spectrometer and IR LED 3 . Proof of concepts are demonstrated, but current state-of-the-art materials do not reach the desired energy efficiency, mostly due to the low absorption strength of the parity-forbidden 3 d –3 d transitions of the Cr 3+ or Mn 2+ ions that are used 4 – 10 . Alternatively, near-IR parity-allowed Eu 2+ 5 d –4 f emission has been recently proposed 11 .…”
Section: Introductionmentioning
confidence: 99%
“…Large efforts have already been undertaken to optimize IR luminescent materials for the above-mentioned applications, starting from the well-known luminescence transitions such as 3 d –3 d , 4 f –4 f , or 5 d –4 f 4 – 10 , 13 , 20 . On the contrary, charge transfer (CT) states have remained below the radar because they often cause luminescence quenching, rather than generating luminescence themselves.…”
Efficient broadband infrared (IR) light-emitting diodes (LEDs) are needed for emerging applications that exploit near-IR spectroscopy, ranging from hand-held electronics to medicine. Here we report broadband IR luminescence, cooperatively originating from Eu
2+
and Tb
3+
dopants in CaS. This peculiar emission overlaps with the red Eu
2+
emission, ranges up to 1200 nm (full-width-at-half-maximum of 195 nm) and is efficiently excited with visible light. Experimental evidence for metal-to-metal charge transfer (MMCT) luminescence is collected, comprising data from luminescence spectroscopy, microscopy and X-ray spectroscopy. State-of-the-art multiconfigurational ab initio calculations attribute the IR emission to the radiative decay of a metastable MMCT state of a Eu
2+
-Tb
3+
pair. The calculations explain why no MMCT emission is found in the similar compound SrS:Eu,Tb and are used to anticipate how to fine-tune the characteristics of the MMCT luminescence. Finally, a near-IR LED for versatile spectroscopic use is manufactured based on the MMCT emission.
“…The total radiant flux of the IR part of the emission amounts to 38 mW. This value surpasses the current Cr 3+ -based state-of-the-art, having IR radiant fluxes in the range of 20–25 mW 4 – 6 , 8 – 10 , by 50%. Fig.…”
Section: Resultsmentioning
confidence: 76%
“…The broadband IR MMCT emission is now applied to construct an IR pc-LED that can directly be used for the numerous above-mentioned spectroscopic applications. Because of the high absorption strength of the parity-allowed 4 f −5 d transitions of Eu 2+ , higher external quantum efficiencies can be achieved than with the current state-of-the-art, Cr 3+ -based phosphors 4 – 6 , 8 – 10 . Furthermore, the extremely broad MMCT emission extends the covered spectral range by several hundreds of nanometers to the IR compared to red/near-IR single Eu 2+ 5 d −4 f emission 11 .…”
Section: Resultsmentioning
confidence: 99%
“…A large market that is presently explored is IR LEDs for the use in smart devices (e.g., mobile phones) to analyze food: information about its freshness, caloric value, or allergen content can be derived from the built-in spectrometer and IR LED 3 . Proof of concepts are demonstrated, but current state-of-the-art materials do not reach the desired energy efficiency, mostly due to the low absorption strength of the parity-forbidden 3 d –3 d transitions of the Cr 3+ or Mn 2+ ions that are used 4 – 10 . Alternatively, near-IR parity-allowed Eu 2+ 5 d –4 f emission has been recently proposed 11 .…”
Section: Introductionmentioning
confidence: 99%
“…Large efforts have already been undertaken to optimize IR luminescent materials for the above-mentioned applications, starting from the well-known luminescence transitions such as 3 d –3 d , 4 f –4 f , or 5 d –4 f 4 – 10 , 13 , 20 . On the contrary, charge transfer (CT) states have remained below the radar because they often cause luminescence quenching, rather than generating luminescence themselves.…”
Efficient broadband infrared (IR) light-emitting diodes (LEDs) are needed for emerging applications that exploit near-IR spectroscopy, ranging from hand-held electronics to medicine. Here we report broadband IR luminescence, cooperatively originating from Eu
2+
and Tb
3+
dopants in CaS. This peculiar emission overlaps with the red Eu
2+
emission, ranges up to 1200 nm (full-width-at-half-maximum of 195 nm) and is efficiently excited with visible light. Experimental evidence for metal-to-metal charge transfer (MMCT) luminescence is collected, comprising data from luminescence spectroscopy, microscopy and X-ray spectroscopy. State-of-the-art multiconfigurational ab initio calculations attribute the IR emission to the radiative decay of a metastable MMCT state of a Eu
2+
-Tb
3+
pair. The calculations explain why no MMCT emission is found in the similar compound SrS:Eu,Tb and are used to anticipate how to fine-tune the characteristics of the MMCT luminescence. Finally, a near-IR LED for versatile spectroscopic use is manufactured based on the MMCT emission.
“…Numerous studies on exploring NIR phosphors have been realized by doping transition metal ions (Cr 3+ , Ni 2+ , and Mn 4+ ), Bi 3+ or rare earth ions (Pr 3+ , Nd 3+ , Tm 3+ , and Yb 3+ ) into inorganic host materials 13–19 . However, the sharp line emission of rare earth ions with 4 f -4 f transition is not broad enough for the desired applications, and the absorption region is also very narrow and weak.…”
Near-infrared luminescent materials exhibit unique photophysical properties that make them crucial components in photonic, optoelectronic and biological applications. As broadband near infrared phosphors activated by transition metal elements are already widely reported, there is a challenge for next-generation materials discovery by introducing rare earth activators with 4f-5d transition. Here, we report an unprecedented phosphor K3LuSi2O7:Eu2+ that gives an emission band centered at 740 nm with a full-width at half maximum of 160 nm upon 460 nm blue light excitation. Combined structural and spectral characterizations reveal a selective site occupation of divalent europium in LuO6 and K2O6 polyhedrons with small coordination numbers, leading to the unexpected near infrared emission. The fabricated phosphor-converted light-emitting diodes have great potential as a non-visible light source. Our work provides the design principle of near infrared emission in divalent europium-doped inorganic solid-state materials and could inspire future studies to further explore near-infrared light-emitting diodes.
The discovery of highly efficient broadband near infrared (NIR) emission material is urgent and crucial for constructing NIR lighting sources and emerging applications. Herein, a series of NIR emission hexafluorides A2BMF6:Cr3+ (A = Na, K, Rb, Cs; B = Li, Na, K, Cs; M = Al, Ga, Sc, In) peaking at ≈733–801 nm with a full width at half maximum (FWHM) of ≈98–115 nm are synthesized by a general ammonium salt assisted synthesis strategy. Benefiting from the pre‐ammoniation of the trivalent metal sources, the Cr3+ can be more efficiently doped into the A2BMF6 and simultaneously prevent the generation of the competitive phase. Particularly, Na3ScF6:Cr3+ (λem = 774 nm, FWHM ≈ 108 nm) with optimal Cr3+‐doping concentration of 35.96% shows a high internal quantum efficiency of 91.5% and an external quantum efficiency of ≈40.82%. A lighting emitting diode (LED) device with a NIR output power of ≈291.05 mW at 100 mA driven current and high photoelectric conversion efficiency of 20.94% is fabricated. The general synthesis strategy opens up new avenues for the exploration of Cr3+‐doped high efficiency phosphors, and the as‐obtained record NIR output power demonstrates for NIR LED lighting sources applications.
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