Cr,Yb-codoped Ca2LaHf2Al3O12 garnet phosphor: electronic structure, broadband NIR emission and energy transfer properties

Realize short-wave infrared luminescence in NaScP2O7:Cr3+,Yb3+ phosphor: Spectral and energy transfer

Short-wave infrared emitting phosphors have extensive applications for spectroscopy technology. The near-infrared phosphor NaScP2O7:Cr3+ that we present in this work has a full width at half maximum (FWHM) of approximately 196 nm, which ranges from 700 to 1200 nm. To achieve efficient short-wave infrared, Yb3+ ions were co-doped. The NaScP2O7:Cr3+,Yb3+ material emitted infrared bands with peaks at 970 and 1003 nm upon excitation at450 nm. Benefitting from energy transfer (ET), the light in the 900-1200 nm from Yb3+ is effectively enhanced. Photoluminescence spectra, thermal quenching, and decay curves of Cr3+/Yb3+ single and codoped NaScP2O7 were investigated. An internal quantum yield of 29.6 % wasdemonstrated by the optimized phosphor NaScP2O7:Cr3+,Yb3+. Furthermore, The final fabrication of the short-wave infrared pc-LED was done through the combination of a blue-emitting chip and NaScP2O7:Cr3+,Yb3+ phosphor, thereby showing great promise for real implementations.

Hydrothermal synthesis of ZnGa2O4 nanophosphors with high internal quantum efficiency for near-infrared pc-LEDs

NIR luminescent materials have garnered widespread attention because of their exceptional properties, with high tissue penetration, low absorption and high signal-to-noise ratio in the field of optical imaging. However, producing nanophosphors with high quantum yields of emitting infrared light with wavelengths above 1000 nm remains a significant challenge. Here, we prepared a nanoscale ZnGa2O4:xCr3+,yNi2+ phosphor with good luminescence performance in near-infrared emission, which was synthesized via a hydrothermal method and subsequent calcination process. By co-doping with Cr3+ and Ni2+, the ZnGa2O4 phosphor shows a strong broadband emission of 1100-1600 nm in the second near-infrared (NIR-II) region, owing to the energy transfer from Cr3+ to Ni2+ with an efficiency up to 90%. Meanwhile, a near-infrared phosphor-conversion LED (NIR pc-LED) device is fabricated based on the ZnGa2O4:0.8%Cr3+,0.4%Ni2+ nanophosphor, which has under 100 mA input current, an output power of 23.99 mW, and a photoelectric conversion efficiency of 7.53%, and can be effectively applied in imaging and non-destructive testing. Additionally, the intensity ratio of INi/ICr of ZnGa2O4:0.8% Cr3+,0.4%Ni2+ with its high sensitivity value of 4.21% K-1 at 453 K under 410 nm excitation, indicates its potential for thermometry application.

Valence conversion and site reconstruction in near-infrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

Achievement of high photoluminescence quantum efficiency and thermal stability is challenging for near-infrared (NIR)-emitting phosphors. Here, we designed a "kill two birds with one stone" strategy to simultaneously improve quantum efficiency and thermal stability of the NIR-emitting Ca3Y2-2x(ZnZr)xGe3O12:Cr garnet system by chemical unit cosubstitution, and revealed universal structure-property relationship and the luminescence optimization mechanism. The cosubstitution of [Zn2+-Zr4+] for [Y3+-Y3+] played a critical role as reductant to promote the valence transformation from Cr4+ to Cr3+, resulting from the reconstruction of octahedral sites for Cr3+. The introduction of [Zn2+-Zr4+] unit also contributed to a rigid crystal structure. These two aspects together realized the high internal quantum efficiency of 96% and excellent thermal stability of 89%@423 K. Moreover, information encryption with "burning after reading" was achieved based on different chemical resistance of the phosphors to acid. The developed NIR-emitting phosphor-converted light-emitting diode demonstrated promising applications in bio-tissue imaging and night vision. This work provides a new perspective for developing high-performance NIR-emitting phosphor materials.

Enabling Yb3+ Luminescence with Visible Light Response in Mg2GeO4 via Energy Transfer

The growing demand for spectroscopy applications in the areas of bioimaging, food quality analysis, and temperature sensing has led to extensive research on infrared light sources. It is crucial for the design of cost-effective and high-performance systems that phosphors possess the ability to absorb blue light from commercial LEDs and convert the excitation energy to long-wavelength infrared luminescence. In this work, we obtained Yb3+ luminescence with visible light response by utilizing the energy transfer from Cr3+ to Yb3+ in Mg2GeO4. After the introduction of Yb3+, intense NIR luminescence peaking at 974 nm can be achieved with an increasing intensity. The local structure analysis was performed to investigate the preferential occupation of Yb3+ ions and the energy transfer process in Mg2GeO4. Considering the properties of thermally coupled anti-Stokes and Stokes emissions of Yb3+ and the sensitive variation of the emission intensity, the potential application of Mg2GeO4:Cr3+, Yb3+ as thermometers was demonstrated.

Rapid Discovery of Efficient Long-Wavelength Emission Garnet:Cr NIR Phosphors via Multi-Objective Optimization

High-efficiency long-wavelength emission near-infrared (NIR) phosphors are the key to next-generation LED light sources. However, high-efficiency phosphors usually exhibit narrow-band emission at shorter wavelengths due to the crystal field intensity. In this paper, we utilize multi-objective optimization to discover the NIR phosphor Gd₃Mg_0.5Al_1.5Ga_2.5Ge_0.5O₁₂:0.04Cr³⁺. It exhibits a broadband NIR emission from 650 to 1100 nm peaking at 763 nm, with a full width at half maximum (FWHM) of 150 nm, an internal quantum efficiency (IQE)/external quantum efficiency (EQE) of 90%/53.1%, and good thermal stability (85.3% @ 150 °C). The packaging results show that ∼53.2 mW of output power is achieved at 915 mW input power, which suggests promising applications for NIR pc-LED. Our approach is based on the data of emission wavelength (WL) and IQE for garnet:Cr NIR phosphors to construct machine learning models. An active learning strategy is used to make tradeoffs between WL and IQE, and we are able to find the targeted phosphor after only four iterations of synthesis and characterization.

Molten Salt Synthesis of Broad-Band Near-Infrared InBO3:Cr3+ Submicron Phosphor and Its Luminescent Enhancement by Lanthanide Ion Codoping

Phosphor materials with small particle sizes and high luminescent efficiency are desired for the fabrication of phosphor-converted light-emitting diodes (pc-LEDs). Near-infrared (NIR) pc-LED light sources have great application potential in the food industry and medical fields, which stimulate the extensive exploration of NIR phosphors. In this work, broad-band NIR-emitting InBO₃:Cr³⁺ phosphors with submicron size and spherical morphology are successfully synthesized via the molten salt method. The InBO₃:Cr³⁺ phosphor exhibits a broad emission band covering 700-1000 nm and peaking at ∼820 nm. The maximum emission intensity is obtained for InBO₃:0.02Cr³⁺ with an internal quantum yield (IQY) of ∼62%, which is higher than that of microsized counterparts derived from solid-state reaction. Furthermore, the absorption and emission enhancements are achieved by codoping lanthanide ions into InBO₃:Cr³⁺ submicron phosphors. The codoping of inert La³⁺ ions can increase the absorption efficiency of InBO₃:Cr³⁺, due to the increased octahedral distortion of Cr³⁺ sites. The codoping of active Yb³⁺ ions can significantly enhance the NIR emissions of InBO₃:Cr³⁺ between 950 and 1100 nm. Meanwhile, the increased IQY of ∼73% is achieved for InBO₃:0.02Cr³⁺,0.005Yb³⁺ simultaneously with suppressed thermal quenching, originating from the effective energy transfer from Cr³⁺ to Yb³⁺ ions.

Blue LED-pumped intense short-wave infrared luminescence based on Cr3+-Yb3+-co-doped phosphors

The growing demand for spectroscopy applications in the areas of agriculture, retail and healthcare has led to extensive research on infrared light sources. The ability of phosphors to absorb blue light from commercial LED and convert the excitation energy into long-wavelength infrared luminescence is crucial for the design of cost-effective and high-performance phosphor-converted infrared LEDs. However, the lack of ideal blue-pumped short-wave infrared (SWIR) phosphors with an emission peak longer than 900 nm greatly limits the development of SWIR LEDs using light converter technology. Here we have developed a series of SWIR-emitting materials with high luminescence efficiency and excellent thermal stability by co-doping Cr³⁺-Yb³⁺ ion pairs into Lu_0.2Sc_0.8BO₃ host materials. Benefitting from strong light absorption of Cr³⁺ in the blue waveband and very efficient Cr³⁺→Yb³⁺ energy transfer, the as-synthesized Lu_0.2Sc_0.8BO₃:Cr³⁺,Yb³⁺ phosphor emits intense SWIR light in the 900-1200 nm from Yb³⁺ under excitation with blue light at ~460 nm. The optimized phosphor presents an internal quantum yield of 73.6% and the SWIR luminescence intensity at 100 °C can still keep 88.4% of the starting value at 25 °C. SWIR LED prototype device based on Lu_0.2Sc_0.8BO₃:Cr³⁺,Yb³⁺ phosphor exhibits exceptional luminescence performance, delivering SWIR radiant power of 18.4 mW with 9.3% of blue-to-SWIR power conversion efficiency and 5.0% of electricity-to-SWIR light energy conversion efficiency at 120 mA driving current. Moreover, under the illumination of high-power SWIR LED, covert information identification and night vision lighting have been realized, demonstrating a very bright prospect for practical applications.

Broadband Near-Infrared-Emitting Phosphors with Suppressed Concentration Quenching in a Two-Dimensional Structure

For inorganic luminescent materials with activators, the energy yield is usually observed to decrease with an increase in activator concentration, which is known as the concentration quenching effect. To inhibit this phenomenon, a common strategy is to increase the distance between activators. Most previous reports have focused on the three-dimensional crystal lattice, and there have been few reports about two-dimensional layered structure. Herein, we synthesized a novel Cr³⁺-activated near-infrared (NIR) phosphor Li₂Sr₂Al(PO₄)₃ (LSAPO) with layered structure, and in such a two-dimensional structure, we proved experimentally that the concentration quenching was suppressed. Under 460 nm excitation, LSAPO:Cr³⁺ gave a broad NIR emission band (700-1200 nm) centered at 823 nm with a full width at half-maximum (fwhm) of 178 nm and a broad absorption band, indicating its potential application in NIR spectroscopy. Moreover, by codoping Cr³⁺ and Yb³⁺ ions, we further widened the emission bandwidth to ∼230 nm of fwhm, the internal quantum efficiency increased from 54% to 61%, and the thermal stability was improved. The fabricated NIR device with a LSAPO:Cr³⁺,Yb³⁺ phosphor coupled with blue chips can be applied in night-vision technologies and medical fields.

Simultaneous enhancement of near infrared luminescence and stability of Cs2AgInCl6:Cr3+ double perovskite single crystals enabled by a Yb3+ dopant

Cs2AgInCl6:Cr3+,Yb3+ double perovskite single crystals was prepared by hydrothermal method, which shows NIR emission from 800 to 1400 nm with a peak at 1000 nm and a full-width at half maximum of 188 nm with a higher PLQY of ∼45% excited at 365 nm.

Cr3+-doped InTaO4 phosphor for multi-mode temperature sensing with high sensitivity in physiological temperature range

With the increasing demand for non-contact temperature sensing, the development of optical thermometer with excellent performance is more and more compelling. Cr3+-doped InTaO4 phosphor was prepared for the implementation of...

Highly thermally stable Cr3+ and Yb3+ codoped Gd2GaSbO7 phosphors for broadband near-infrared applications

Gd₂GaSbO₇:Cr³⁺,Yb³⁺ phosphors with efficient broadband NIR emission were prepared by a solid-state reaction. Under the excitation of 448 nm, the Gd₂GaSbO₇:Cr³⁺ (GGS:Cr³⁺) phosphor exhibits a broadband NIR emission band centered at approximately 770 nm with a full width at half maximum (FWHM) of 160 nm. In addition, Yb³⁺ codoping can distinctly improve the photoluminescence properties of the GGS:Cr³⁺ phosphor, leading to broadening of the FWHM and greatly enhancing the thermal stability of the phosphor. Moreover, the energy conversion process of Cr³⁺ → Yb³⁺ ions was analyzed in detail, demonstrating that the energy transfer mechanism conformed to electric dipole-dipole interaction. The NIR pc-LEDs assembled with the GGS:Cr³⁺ phosphor and blue LED chips possessed a maximum NIR output power of ∼21 mW at 100 mA driving current, indicating promising applications of the synthesized phosphor in NIR pc-LEDs.

Broadband near-infrared BaMSi3O9:Cr3+ (M = Zr, Sn, Hf) phosphors for light-emitting diode applications

Cr3+-Doped BaMSi3O9 (M = Zr, Sn, Hf) NIR-emitting phosphors have been developed, which exhibit a broad NIR emission band over 650–1200 nm with a tunable band maximum longer than 800 nm and a FWHM of more than 155 nm upon blue light excitation.