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 optimized phosphor, a NIR pc‐LED with photoelectric efficiencies of 21.28%@10 mA, 15.75%@100 mA and NIR output powers of 46.09 mW@100 mA, 54.29 mW@130 mA is fabricated. The high power NIR light is observed to penetrate upper arms (≈8 cm). For application in NIR spectroscopy, the NIR pc‐LED is used as light source to measure transmission spectra of water, alcohol, and bovine hemoglobin solution. These results indicate the NIR garnet phosphor to be a promising candidate for NIR pc‐LED.
Far‐red (FR) phosphor‐converted light‐emitting diodes (pc‐LEDs) driven by blue LED chips are novel light sources for applications in phototherapy, photosynthesis, natural light simulation, and so on but still bear low electricity‐to‐FR light conversion efficiency (≤ 23%) due to deficiency of phosphors that have both high blue light absorptance and high FR internal quantum efficiency (IQE) for the realization of efficient blue to FR conversion. FR Ca3Sc2Si3O12 (CSSG):Cr3+ garnet phosphor has ultra‐high IQE (> 90%) but low blue light absorption. Here, a twofold increase of blue light absorption cross‐section is reported with still high FR IQE via Lu3+−Mg2+ substitution for Ca2+−Sc3+ in CSSG:Cr3+ to form Ca3–xLuxMgxSc2–xSi3O12:Cr3+ garnet solid solution, which is attributed to enhanced mixing of odd‐parity configuration into 3d configuration of Cr3+ induced by the cations substitution. Optical properties, crystal field strengths, and thermal stabilities of the solid solution phosphors are studied as a function of x. After complete replacement of Sc3+, the as‐fabricated FR pc‐LED emits at 750 nm with 65.7% blue‐to‐FR quantum conversion efficiency and consequently offers an electricity‐to‐FR light conversion efficiency over 30%. Moreover, the solid solution phosphors show high quenching temperatures in the range of 580–610 K. The results can advance the development of efficient FR phosphors and pc‐LEDs for various applications.
Phosphor‐converted light‐emitting diodes (pc‐LEDs) with broadband near‐infrared (NIR) emission have emerged as compact light sources for portable NIR spectroscopy. However, the associated broadband NIR phosphors suffer from low quantum efficiency (QE) and severe thermal quenching. Here the realization of highly efficient (internal QE ≈ 90%) and nearly zero‐thermal‐quenching broad NIR emission in Cr3+ and Yb3+ codoped Gd3Sc1.5Al0.5Ga3O12 (GSGG) via efficient energy transfer from Cr3+ to Yb3+ is reported, whereby a high‐performance NIR pc‐LED is obtained that can generate ultra‐broad‐band NIR emission covering the whole range of 700−1100 nm with high output power (50 mW at a current of 100 mA) and high photoelectric efficiency (24% at a current of 10 mA). The results not only demonstrate that Cr3+ and Yb3+ codoped GSGG has great potential for compact NIR light sources, but also indicate that the strategy of energy transfer can be exploited for developing new NIR phosphors with both high QE and thermal stability.
Super broadband near‐infrared (NIR) phosphor converted light‐emitting diodes (pc‐LEDs) are future light sources in NIR spectroscopy applications such as food testing. At present, a few blue LED excitable super broadband NIR phosphors (bandwidth > 300 nm) have been developed producing the NIR output powers below 26 mW at 100 mA input current after LED packaging. Here, an efficient super broadband NIR phosphor achieved by doping Yb3+ is reported in the NIR Ca2LuZr2Al3O12:Cr3+ (CLZA:Cr3+) garnet phosphor developed previously. Benefited from the superposition of Cr3+ emission and highly efficient Yb3+ emission excited by energy transfer from Cr3+, the codoped CLZA:Cr3+,Yb3+ phosphor shows a bandwidth of 320 nm and an internal quantum efficiency of 77.2% both higher than that (150 nm and 69.1%) of singly doped CLZA:Cr3+ phosphor. The codoped phosphor converts LED produced 41.8 mW NIR output at 100 mA input current. The pc‐LED as a light source is also well applied to the NIR transmission spectra measurement of water. The results indicate the great potential of CLZA:Cr3+,Yb3+ phosphor in super broadband NIR pc‐LED applications.
Bright red upconversion phosphor Ba3Y4O9:Er3+/Yb3+ and dual-color complementary optical thermometry to maintain relatively high sensitivities over a wide temperature scope.
Laser-driven (LD) lighting is emerging as the next-generation high-power solid-state lighting technology. All-inorganic color converters with high quantum efficiency (QE), small thermal quenching, high thermal conductivity, and high thermal and chemical stabilities are crucial to coping with the enormous heat generated in LD lighting. Although luminescent translucent ceramics are the most promising class of color converters, only green/ yellow-emitting ones with satisfactory performance are developed before. Here, a far-red-emitting composite ceramics Y 3 Al 5 O 12 (YAG)-Al 2 O 3 :Cr 3+ with near-unity internal QE and zero-thermal quenching are prepared via pressureless glass crystallization, where the inside light scattering is finely tuned by simply manipulating the temperature to induce controllable grain growth. The commonly used inert matrix Al 2 O 3 here becomes an optically active component as YAG, thus alleviating the undesired concentration quenching while maintaining strong light absorption. Therefore, a high-power LD far-red lighting source with luminescence saturation threshold up to 21.4 W mm −2 is demonstrated, which may find broad applications in plant growth lighting, solar simulators, and phototherapy.
The photoluminescence of Ti4+ and Eu3+ in monoclinic ZrO2 was demonstrated for optical thermometry through energy transfer from titanium–oxygen complexes to Eu3+.
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