Broadband Near-infrared Light Source Research Articles

Cr3+ activated Gd3Sc2Al3O12 garnet phosphor ceramic with broadband emissions and enhanced thermal stability toward high-power near-infrared LED/LD

The development of high-quality phosphor ceramics with high photoelectric efficiencies and thermal stabilities is essential for realizing high-power broadband near-infrared light sources. In this study, a series of pure-phase Gd3Sc2Al3O12:Cr3+ near-infrared (NIR) phosphor ceramics (GdScCr NIR-PCs) exhibiting remarkable thermal stability and broadband emission were fabricated for the first time using a vacuum sintering technique. The integrated emission intensity at 423 K is 79.8 % of that at room temperature. The GdSc08Cr exhibits an emission peak at a wavelength of 785 nm, with a full width at half maximum (FWHM) of 116.9 nm under 460 nm excitation. By integrating the GdScCr NIR-PC with a blue light-emitting diode/laser diode (LED/LD) excitation source, the NIR LED prototype achieved a maximum output power of 112.19 mW at 300 mA with a photoelectric conversion efficiency of 13.64 % at 150 mA, and the NIR LD prototype achieved a maximum power output of 484.34 mW at 2.3 A. The operating temperatures of NIR-PCs were 73.1 °C at 300 mA for LED and 90.7 °C at 2.5 A for LD. Moreover, the application of the prepared GdScCr NIR-PCs for fruit and grain detection was performed. These results demonstrate that the prepared GdScCr NIR-PCs possess substantial potential for application in high-power broadband NIR spectroscopy.

Laser-driven broadband near-infrared light source with watt-level output

Laser-driven broadband near-infrared light source with watt-level output

Boosting Continuous-Wave Laser-Driven Nonlinear Photothermal White Light Generation by Nanoscale Porosity.

The irradiation of an optically absorptive medium by a continuous-wave (CW) near-infrared (NIR) laser can result in a spectral continuum emission covering both the visible and NIR regions, which is attractive for applications as continuum light sources in diverse fields. It is shown here that this NIR-laser-driven light emission can be effectively modulated with nanoscale architecture in the medium. By using porous silica as the model matrix and Yb3+ ions as the photothermally active centers, up to 100 folds increment in NIR-laser-induced emission intensity and dramatic decrease in threshold excitation density are demonstrated. It is observed that the emission intensity exhibits a strong nonlinear dependence on the power of the NIR excitation laser, featuring clear excitation power thresholds. Based on combined numerical simulation and spectral and temperature measurements, the improved broadband emission and photothermal nonlinearity are interpreted by enhanced optical energy localization around the laser spot that results in boosting the photon-to-photon conversion efficiency. The use of the nonlinear photothermal emission process as a broadband NIR light source, which could be exploited for applications including NIR spectroscopy, imaging, and sensing, is further demonstrated as a proof-of-concept.

Photothermal properties of stable aggregates of gold nanorods

Aggregation of the nanoparticles is a natural phenomena due to various biological and physical parameters but these aggregates are highly unstable. If aggregates would have been stable then it might be useful for some biomedical applications. To study the optical properties and photothermal heat generation of stable aggregates of the metal nanoparticles, we present a forced synthesis of aggregates of small gold nanorods in a mixture of Dulbecco’s Modified Eagle’s medium (DMEM) and Bovine Serum Albumin (BSA). We synthesized hexadecyltrimethylammonium bromide (CTAB) coated gold nanorods and then prepared the stable aggregates to study the optical characteristics of these aggregates. Absorption spectra of aggregates show the redshift compared to the monodispersive gold nanorods and confirm that the shape and size of aggregate depend on the amount of BSA in DMEM as well as on the concentration of CTAB in the stock solution of the gold nanorods suspension. The higher concentration of the BSA in DMEM and lower concentration of CTAB of monodispersive gold nanorod suspension causes greater redshift. We tuned the well defined plasmonic absorption resonance peaks of the aggregates of gold nanorods up to the second biological therapeutic window. We studied the stability of the synthesized aggregates of gold nanorods for up to one week and found that the aggregates were stable for at least one week. A photothermal study of these aggregates was also carried out using high power broadband near-infrared light source. Aggregates were also photothermally stable which warrants their repeated use for such applications. The photothermal conversion efficiency of these stable gold nanorod aggregates were higher than its monodispersive form of the nanorods. The present study on the optical and photothermal properties of stable aggregates could be useful for biomedical therapeutic applications, sensing, deep tissue light penetration for imaging and other scientific applications to redshift the plasmonic absorption resonance peak and enhance the photothermal effect.

D2h-Symmetric Tetratellurium Clusters in Silicate Glass as a Broadband NIR Light Source for Spectroscopy Applications.

Broadband near-infrared (NIR) light sources present attractive opportunities for potential applications in high-capacity telecommunication, temperature sensing, energy conversion, and NIR spectroscopy. While significant effort has been spent on materials doped with rare-earth and transition-metal ions, the achievement of these materials with ultrabroadband NIR emission and desired wavelength region remains a long-standing challenge, especially operating in the spectral region between 700 and 1300 nm. Here, such emission is developed in tellurium (Te) cluster-doped silicate glass for the first time. Furthermore, the mechanism of the NIR luminescence due to D2h-symmetric tetratellurium (Te4) clusters is identified by density functional theory (DFT) calculations. For intense luminescence, a model for the generation and stabilization of Te clusters by tailoring topological cages via adjustment of the Na2O and Al2O3 contents and by optimizing the content of the dopant is proposed. Various stable Te clusters embedded into glass exhibit intense visible (Vis) to NIR broadband luminescence (400-1300 nm) with a spectral gap of 900 nm. In a demonstration experiment, a light-emitting diode (LED) device is fabricated from Te cluster-doped glass. This study opens a new opportunity for Te cluster-doped glass as a broadband NIR light source for spectroscopy applications.

Broadband near-infrared emitting from Li1.6Zn1.6Sn2.8O8:Cr3+ phosphor by two-site occupation and Al3+ cationic regulation

Broadband sources of near-infrared (NIR) radiation have garnered considerable attention in medical applications and non-destructive analysis. In this work, we have synthesized a lithium zinc stannate phosphor Li1.6Zn1.6Sn2.8O8:Cr3+ (LZSO:Cr) for broadband NIR light sources. The LZSO:Cr phosphor exhibited broadband excitation band matches exceptionally well with the emission of commercial 450-nm blue light-emitting diode (LED) chips. As expected, the broadband emission of infrared radiation from 650 nm to 1200 nm was realized due to the unique crystal field environment, where Cr3+ ions were substituted in two distorted octahedral sites. The broad emission spectrum exhibited peaks around 830 nm and 930 nm with a full width at half maximum (FWHM) of ~190 nm and internal quantum efficiency of 53%. The FWHM could be tuned to ~220 nm by co-doping with Al3+ ions because of the crystal splitting. The luminescence properties including excitation, emission, decay time, and their relationship between the lattice crystal properties have also been investigated. A phosphor-converted LED (pc-LED) was packaged by combining the phosphor with a 450-nm blue LED chip, which proves the feasibility of our design strategy for broadband NIR light sources.

(INVITED) Recent progress on broadband near-infrared phosphors-converted light emitting diodes for future miniature spectrometers

The development of phosphor-converted technology-based broadband near-infrared light source for miniature spectrometers to perform spectroscopy applications has recently attracted remarkable attention among researchers in the academe and industry. The transition metal element Cr3+-activated luminescent materials act as the potential candidates to meet the demands for increased near-infrared light spectral distribution. In this mini-review, the most recently developed broadband near-infrared phosphors activated by Cr3+ are listed and classified according to their major chemical element constituents. In addition to the luminescence mechanism of Cr3+, the association between the number of crystallographic sites and spectral distribution of near-infrared light is mainly reviewed with the example of known near-infrared phosphors, which may be helpful in exploring future broadband near-infrared phosphors. Finally, the performance-evaluating parameters of phosphor-converted near-infrared light-emitting diode are discussed and compared with those of known broadband near-infrared phosphors for spectroscopy applications.

Preface to Special Issue on Development of Broadband Near-Infrared Light Source and Its Applications

Preface to Special Issue on Development of Broadband Near-Infrared Light Source and Its Applications

Broadband near-infrared light source derived from Cr3+-doped phosphors and a blue LED chip.

NIR-emitting YAl3(BO3)4:Cr3+/Yb3+ (YAB:Cr/Yb) and NaScSi2O6:Cr3+ (BSSO:Cr) phosphors were demonstrated as luminescent converters for broadband NIR phosphor-converted LEDs (pc-LEDs). YAB:Cr/Yb phosphors show emissions in 670-800nm (Cr3+ emission) and 950-1050nm (Yb3+ emission) upon excitation at 450nm. In the BSSO host, Cr3+ ions occupy Sc3+ sites with relatively weak crystal field, and thus a broadband Cr3+ emission at longer wavelengths of 750-950nm is found for BSSO:Cr phosphors. Moreover, temperature-dependent spectral studies indicate that both YAB:Cr/Yb and BSSO:Cr phosphors exhibit good thermal stability, and more than 80% of the initial emission intensities can be sustained at 150°C. A NIR pc-LED prototype was fabricated by integrating these two phosphors with a blue LED chip (∼450 nm), which generated a broadband emission in the NIR spectral range from 780 to 1050nm. A NIR light output power of ∼26 mW was achieved at the injection current of 100mA, with the corresponding energy conversion efficiency of ∼8.6%.

Temperature dependent photoluminescence of Cr3+ doped Sr8MgLa(PO4)7

Broad band near infrared (NIR) light sources are currently of great interest in many application areas, especially in near infrared spectroscopy (NIRS). Due to the declining availability of incandescent and halogen light sources, there is a strong demand for other efficient broad band NIR light sources. NIR phosphor converted (pc) LEDs are presently explored to realize efficient broadband NIR sources. Herein, we report on the luminescence properties of Cr3+ doped Sr8MgLa(PO4)7 (SMLP) which is a potential luminescent converter for high power broad band NIR pcLEDs. Microcrystalline powders of SMLP doped with different Cr3+ concentration were synthesized by solid state reactions and exhibit efficient near infrared broad band emission upon excitation in the blue/cyan spectral range. The emission extends from 700 to 1000 nm (FWHM = 140 nm) and is assigned to the spin-allowed 4T2→4A2 transition of Cr3+. The optical properties of Cr3+ ions in SMLP were examined in terms of spectroscopic parameters such as crystal field strength, Racah parameters, and phonon coupling parameters. The photoluminescence quenching temperature (T1/2) is a crucial parameter for blue to NIR radiation converters as the high power (In,Ga)N LEDs (pumping source) reach junction temperatures up to ∼450 K. The Sr8MgLa(PO4)7:Cr3+ phosphors reveal rather low quenching temperatures (T1/2 ≅ 300 K) mainly due to a strong electron-phonon coupling, while the presented results provide insight in factors determining thermal quenching.

Growth of quantum three-dimensional structure of InGaAs emitting at ~1 µm applicable for a broadband near-infrared light source

We obtained a high-intensity and broadband emission centered at ~1µm from InGaAs quantum three-dimensional (3D) structures grown on a GaAs substrate using molecular beam epitaxy. An InGaAs thin layer grown on GaAs with a thickness close to the critical layer thickness is normally affected by strain as a result of the lattice mismatch and introduced misfit dislocations. However, under certain growth conditions for the In concentration and growth temperature, the growth mode of the InGaAs layer can be transformed from two-dimensional to 3D growth. We found the optimal conditions to obtain a broadband emission from 3D structures with a high intensity and controlled center wavelength at ~1µm. This method offers an alternative approach for fabricating a broadband near-infrared light source for telecommunication and medical imaging systems such as for optical coherence tomography.

Integration of Emission-Wavelength-Controlled InAs Quantum Dots for Ultra-Broadband Near-Infrared Light Source

Near-infrared (NIR) light sources are widely utilized in biological and medical imaging systems owing to their long penetration depth in living tissues. In a recently developed biomedical non-invasive cross-sectional imaging system, called optical coherence tomography (OCT), a broadband spectrum is also required, because OCT is based on low coherence interferometry. To meet these operational requirements, we have developed a NIR broadband light source by integrating self-assembled InAs quantum dots (QDs) grown on a GaAs substrate (InAs/GaAs QDs) with different emission wavelengths. In this review, we introduce the developed light sources and QD growth techniques that are used to control the emission wavelength for broadband emission spectra with center wavelengths of 1.05 and 1.3 μm. Although the strain-induced Stranski-Krastanov (S-K) mode-grown InAs/GaAs QDs normally emit light at a wavelength of around 1.2 μm, the central emission wavelength can be controlled to be between 0.9–1.4 μm by the use of an In-flush technique, the insertion of a strain-reducing layer (SRL) and bi-layer QD growth techniques. These techniques are useful for applying InAs/GaAs QDs as NIR broadband light sources and are especially suitable for our proposed spectral-shape-controllable broadband NIR light source. The potential of this light source for improving the performance of OCT systems is discussed.

Growth of InAs/GaAs quantum dots with central emission wavelength of 1.05 μm using In-flush technique for broadband near-infrared light source

Self-assembled InAs quantum dots (QDs) emitting at around 1.05μm in wavelength were grown on a GaAs substrate by using the In-flush technique. A rapid annealing (In-flush) process after the growth of the GaAs capping layer, which partially covers InAs-QDs, reduces the height of the InAs-QDs to the thickness of the capping layer. Using this approach, the emission wavelengths of the QDs were precisely controlled by varying the thickness of the capping GaAs layer. The central emission wavelength was suitably controlled in the range of approximately 1.22–0.95μm. This method enables the realization of a broadband 1.05μm light source with a bandwidth of beyond 200nm via a combination of In-flushed QDs. Such a broadband light source of 1.05μm in wavelength is applicable to optical coherence tomography (OCT), thereby enabling high-resolution and large penetration depth in the OCT images. In addition, we found that a higher emission intensity of the In-flushed QDs can be obtained by reducing the annealing temperature of the In-flush process.

Imaging of subcutaneous blood vessels and flow velocity profiles by optical coherence tomography

We have applied a compact low power rapid scanning Doppler Optical Coherence Tomography system to monitor multi-dimensional velocity profiles within the complex vessels and simultaneous real-time non-invasive imaging of skin tissues morphology in vivo, in the wavelength range of 1.3–1.5 nm. Optical clearing of skin tissues has been utilized to achieve depth of OCT images up to 1.7 mm. Current approach enables applying low-power (0.4–0.5 mW) and low-noise broadband near-infrared light sources and obtaining OCT images with down to 12 μm spatial resolution. Two-dimensional time-domain OCT images of complex flow velocity profiles in blood vessel phantom and in vivo subcutaneous human skin tissues are presented. The effect of optical clearing on in vivo images is demonstrated and discussed.

Bi-doped BaF_2 crystal for broadband near-infrared light source

Bi-doped BaF(2) crystal was grown by the temperature gradient technique and its spectral properties were investigated. The absorption, emission and excitation spectra were measured at room temperature. Two broadband emissions centered at 1070 and 1500 nm were observed in Bi-doped BaF(2) crystal. This extraordinary luminescence should be ascribed to Bi-related centers at distinct sites. We suggest Bi(2+) or Bi(+) centers adjacent to F vacancy defects are the origins of the observed NIR emissions.

Transparent Ni2+-doped lithium-alumino-silicate glass-ceramics for broadband near-infrared light source

Broadband infrared luminescence centred at around 1300 nm with full-width at half maximum of about 342 nm was observed from transparent Ni2+-doped lithium-alumino-silicate glass-ceramics embedded with β-eucryptite crystallines. The room temperature fluorescent lifetime was 98 µs. The transparent glass-ceramics may have potential applications in a widely tunable laser and a super-broadband optical amplifier for optical communications.

LINEAR POLARIZED LIGHT THERAPY IMPROVES BELL'S PALSY

The SuperLizer™ (SL) is a linearly polarized broad-band near-infrared light source which can deliver a combination of phototherapy and infrared mediated heat therapy in a noninvasive manner. The present study examines the therapeutic effect of SL treatment on Bell's palsy. Fifty patients with Bell's palsy were the subjects of the study and they were randomly allocated to two groups. Group I consisted of 25 patients treated with SL radiation and oral prednisolone administration. Group II consisted of 25 patients treated with oral prednisolone administration alone. The effect of treatment was assessed with electroneurography (ENoG), coupled with the 40 points evaluation scale proposed by Yanagihara. There was no significant difference in Yanagihara's scores and ENoG between groups I and II three months after the onset of the disease in those patients with less than 50% neural degeneration. In patients with more than 50% degeneration, however, Yanagihara's score of 31.7 ± 2.1 (mean ± SEM) in group I was significantly higher than the 25.5 ± 2.4 score of group II at the same post-onset period. The group I ENoG score of 51.4 ± 4.2% was also significantly higher than the 43.0 ± 3.6% score of group II at the three month post-onset period. We conclude that SL radiation combined with prednisolone is a more effective treatment than prednisolone alone in Bell's palsy patients with more than 50% degeneration.