Night-vision Surveillance Research Articles

Modulating Near-Infrared Persistent Luminescence via Diverse Preparation Approaches.

Near-infrared (NIR) persistent luminescence (PersL) materials have attracted extensive attention due to their great promise in medical diagnostics, bio-imaging, night vision surveillance, multi-level anticounterfeiting, and information encryption. To achieve NIR PersL (micro/nano-) materials with the desired properties, a variety of synthesis methods have been employed, including solid-phase reaction and liquid-phase synthesis. Different synthesis methods have different but important effects on the micro/nano-structure, luminescence, and PersL properties of the materials. Moreover, the influence of various synthesis methods on the properties of NIR PersL materials determines the selection of preparation approaches for other new material systems. Taking the representative NIR PersL ZnGa2O4:Cr3+ material as an example, four synthesis procedures are applied, namely, high-temperature solid-state reaction (SSR), high-temperature molten salt method (MSM), hydrothermal method (HM), and microwave-assisted solid-state (MASS) method. The structural and luminescent properties of samples made by SSR, MSM, HM, and MASS are compared. Notably, it is revealed that the MASS method can create additional trapping energy levels, which is of great significance for emerging applications. This work demonstrates the different effects of synthesis methods on PersL performance and provides a good guideline for the rapid and reasonable selection of preparation methods for diverse applications.

Retraction Note: Intelligent model to image enrichment for strong night-vision surveillance cameras in future generation

Retraction Note: Intelligent model to image enrichment for strong night-vision surveillance cameras in future generation

Obtaining versatile Cr3+-activated phosphors with improved far-red emissions via host composition modulation

Cr3+-activated spinel-type phosphors have great potential in different application scenes due to their unique sharp and far-red (FR) emission. However, the multi-functionalization of these phosphors is still limited by their unsatisfied comprehensive properties. Herein, a simple composition engineering was used to explore versatile phosphors, using Ga3+ to substitute Al3+ to improve the optical performances of spinel LiAl5–xGaxO8:Cr3+. The substitution of Ga3+ evidently affects the crystal field environment of Cr3+ and further accounts for the luminescence optimization. Using the optimized phosphor, two sensitive thermometers based on fluorescence intensity ratio (FIR) technique were explored on account of the different temperature dependencies of 4T2→4A2 and 2E→4A2 emission and of R2 and R1 emission. The maximum relative sensitivity Sr are 1.29%/K at 323 K and 1.94%/K at 298 K, respectively, which are superior to that of the Ga3+-unsubstituted one. Besides, the Ga3+→Al3+ substitutions endow the resultant phosphors with larger atomic number (Zeff) and theoretical density, which is more conducive to improving X-ray-stimulated emission for X-ray detection. Finally, the potential applications of the developed phosphor are also reflected in plant growth and night vision surveillance, as it is shown to be capable of matching with the absorption of phytochrome PFR and visualizing objects in the dark. This contribution not only proves that the developed LiAl5–xGaxO8:Cr3+ FR phosphors are promising versatile platforms, but also provides an essential guidance for designing more novel multi-functional materials.

Sol-gel combustion synthesis and near-infrared luminescence of Ni2+-doped MgAl2O4 spinel phosphor

Near-infrared phosphor converted light-emitting diode (NIR pc-LED) has many advantages over traditional NIR light sources, and has broad application prospects in night vision surveillance, non-destructive testing, bioimaging, and other fields. Phosphors are typically synthesized by the high-temperature solid-phase method as chunks or large granules, which need to be ground to small particles for practical application. This process introduces surface defects and reduces the luminous efficiency of phosphors. In this work, near-infrared phosphors composed of spinel MgAl2O4:Ni2+ with particle size less than 100 nm was synthesized in high-purity by sol-gel combustion method using nitrate salts with citric acid were used as raw materials. Under 365 nm excitation, MgAl2O4:Ni2+ phosphors emit broadband near-infrared luminescence of 1000–1600 nm with a width at half maximum of 237 nm. The optimal Ni2+ doping concentration was determined to be 1.5 mol% and the optimal sintering temperature was 1200 °C. The thermal activation energy of this phosphor was found to be 0.409 eV and the phosphor had good luminescence thermal stability. An NIR pc-LED device was assembled from the phosphor and commercially available near-ultraviolet LED, which showed a current-dependent increased of NIR luminescence up to 160 mA and an efficiency drop appeared with further increase of the current, suggesting a thermal dependent quenching may have occurred. On the other hand, the output of NIR luminescence increased nearly linearly with the increased of current when a 360 nm laser diode was used as the excitation light source, indicating the NIR phosphor has a very high fluorescence saturation threshold. Our study provides the utility for the sol-gel method in the preparation and the potential application of the nanoscale NIR-II phosphor materials.

Cooperative cationic substitution strategy triggers high blue-light absorptance and near-infrared emission with high quantum efficiency in Cr3+-activated pyroxene-type assembly

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) assembled with the broadband NIR-emitting phosphors has been a promising light source for application in agricultural plant lighting, night vision, food analysis and medical diagnosis. But it suffers from a low photoelectric efficiency (<30 %) due to deficiency of phosphors with high internal quantum efficiency (IQE) and strong absorption capacity in the blue spectral region. Herein, a broadband NIR-emitting luminescent material capable of efficient blue to NIR light conversion with still high IQE was developed via the chemical-composition engineering of CaMgGe2O6:Cr3+ using cooperative cationic substitution of Ca2+-Mg2+ by Na + -Ga3+. The emission profiles evolved a red-shift from 839 to 859 nm with the full width at half-maximum (FWHM) extending from 161 nm to 177 nm as the increase of [Na+-Ga3+] pairs. In addition, the IQE can be finely adjusted. Importantly, the blue-light absorption efficiency can be greatly improved to 34.8 % upon pumping by the constant excitation energy. The increased local structural distortion induced by introducing [Na+-Ga3+] pairs has been verified for the main factor causing these desirable optical properties change. Benefiting from the improvement of blue-light absorptance, the fabricated NIR pc-LED device via coating the developed phosphor on a blue LED chip achieved the larger photoelectric efficiency 31.2 %@10 mA compared to the previously reported value of 27.2 %@10 mA. The excellent performance of biomedical imaging and night vision surveillance represented by the assembled NIR pc-LED was demonstrated.

High‐Performance NIR Emission in Chromium‐Doped Garnet Phosphors Enabled by Structure and Excitation Regulation

AbstractThe burgeoning phosphor‐converted near‐infrared light‐emitting diodes (pc‐NIR LEDs) have important applications in special illumination and spectroscopy analysis. However, the development of efficient NIR‐emitting phosphors with high performance is still a challenge. In this work, a chemical unit co‐substitution strategy is proposed to realize the excitation transition regulation and successfully achieve high‐performance NIR luminescence in Ca3‐yNayMg1‐ySb2‐xAl2+yO12: xCr3+ (0 ≤ x ≤ 0.05, 0 ≤ y ≤ 1) garnet‐type solid solution phosphors. Through the excitation transition modulation from the 4A2 ground state to the 4T1(4P) and 4T1(4F) excitation state, the excitation intensity at the blue light region is largely enhanced by 25.6 times. Moreover, the NIR‐emitting efficiency and thermal stability are improved, with the optimal luminescence internal quantum efficiency of 90.6% and thermal stability of 97%@423 K, without any flux‐assisted sintering or reduction atmosphere protection. The structure regulation induced small Stokes shift, weak electron‐phonon coupling effect, and decreased non‐radiative transition are responsible for the excellent NIR‐emitting performance. Finally, the NIR pc‐LED is fabricated with photoelectric efficiencies of 18.7%@100 mA and NIR output powers of 63 mW@100 mA, presenting potential applications in nondestructive internal defect detection, veins imaging, and night vision surveillance.

Unlocking long-lasting green luminescence in manganese-doped magnesium gallate

Persistent luminescence (PersL) materials have stimulated substantial interest for a variety of technological applications, such as sustainable night-vision surveillance, optical data storage, in vivo bioimaging, and time–temperature indicators. However, the conventional synthesis procedures are time-consuming and energy inefficient, requiring high production cost and resulting in severe safety risks. Besides, the preparation methods utilized also play an important role in determining the features of structure, morphology, and luminescence, giving rise to additional functionalities, such as PersL. Herein, the green long-lasting luminescence of MgGa2O4:Mn2+ is unlocked via a facile thirty-minute microwave-assisted solid state (MASS) method. This facile MASS technique allows for the preparation of more multi-aperture cluster-like samples with smaller particle sizes. Such unlocked PersL feature is further confirmed from the presence of broad trap distributions within host matrix originating from the increased oxygen vacancies during MASS preparation processes. The phosphors are promising for night vision and information storage applications. This work provides an example of the design of phosphors via a facile preparation method to facilitate additionally optical functionality, unlocking their PersL property in non-PersL materials.

Novel broadband NIR phosphors Y2Mg2Ga2Si2O12:xCr3+ for NIR LED applications.

The Cr3+-doped near-infrared (NIR) phosphors have been extensively investigated owing to their promising applications in biomedicine, food safety detection, and night vision surveillance. However, achieving broadband (FWHM > 160 nm) NIR emission is still challenging. In this paper, novel Y2Mg2Ga2-xSi2O12:xCr3+ (YMGS:xCr3+, x = 0.005-0.08) phosphors were prepared by a high-temperature solid-state reaction. The crystal structure, photoluminescence properties of the phosphor, and the device performance of a pc-LED were researched in detail. When excited at 440 nm, the YMGS:0.04Cr3+ phosphor exhibited broadband emission in the range of 650-1000 nm, peaking at 790 nm with a full width at half-maximum (FWHM) of up to 180 nm. The wide FWHM of YMGS:Cr3+ is conducive to its extensive application in NIR spectroscopic technology. In addition, the YMGS:0.04Cr3+ phosphor could maintain 70% of the initial emission intensity at 373 K. By combining the commercial blue chip with the YMGS:0.04Cr3+ phosphor, the resulting NIR pc-LED demonstrated a near-infrared output power of 14 mW with a photoelectric conversion efficiency of 5% at a drive current of 100 mA. This work provides a broadband emission NIR phosphor option for NIR pc-LED devices.

Watch me sleep: Self-surveillance and aging queer performance anxiety

Watch me sleep is a video essay that compares Restless, a video installation comprised of night-vision surveillance footage of Dayna McLeod and her girlfriend sleeping, with an excerpt of Under Surveillance: 12hrs at the PHI, a live-feed performance that featured her sleeping alone at the PHI Centre—an arts research and exhibition centre in Montreal—that was livestreamed as part of a fifteen-day broadcasting program in February 2021. This video essay puts in conversation different affective moments of sleeping between these projects: one for an installation where the artist had editing control over footage of her sleeping self and what was eventually shown to an audience, and the other, where she had little to no control over what was shown to the original livestreaming audience because she was asleep.

Site-Selective Occupancy Control of Cr Ions toward Ultrabroad-Band Infrared Luminescence with a Spectral Width up to 419 nm.

Infrared-emitting phosphor-converted light-emitting diodes (LEDs) are desirable light sources for a very wide range of applications such as spectroscopy analysis, nondestructive monitoring, covert information identification, and night-vision surveillance. The most important aspect of infrared emitters for spectroscopy is to cover the widest possible wavelength range of emitted light. However, developing ultrabroad-band infrared emitters based on converter technology is still a challenging task due to the lack of suitable phosphor materials that emit in a wide wavelength range upon excitation from blue-emitting chips. Herein, this work demonstrates Cr3+-activated Mg2SiO4 infrared phosphors with a super wide infrared spectral range of 600 to 1400 nm and high internal quantum yield up to 80.4% upon 460 nm excitation. Site-selective occupancy of Cr3+ emitters in two different Mg sites in the Mg2SiO4 lattice results in two distinct broad emission bands peaking at 760 and 970 nm, both of which contribute to the ultrabroad-band infrared luminescence with a full width at half maximum (FWHM) of 419 nm. This is by far the broadest infrared emission to the best of our knowledge. On this basis, an ultrabroad-band infrared LED prototype has been fabricated by the combination of the Mg2SiO4:Cr3+ phosphor with a blue LED chip, which shows great potential for imaging and sensing applications. This work demonstrates that site-selective occupancy control of Cr ions is an effective strategy for developing ultrabroad-band Cr3+-doped phosphors.

Low-energy visible light excitable Bi2+-activated near-infrared persistent phosphors for information encryption application

Near-infrared (NIR, 700–900 nm) emissive persistent phosphors have been given substantial attention in the past decade due to their bright future for many advanced applications from night vision surveillance to biomedical imaging. Here, we report the intense NIR persistent luminescence from a series of Bi2+-activated persistent luminescence materials achieved by the cation disorder strategy in CaSnO3 host. Taking Ca0.95(Na,Gd)0.025SnO3:Bi2+ as an example, it exhibits long-lasting NIR afterglow with a peak maximum at 805 nm assigned to the 2P3/2(1)→2P1/2 transition of Bi2+ and a long persistence time of more than 24 h after the ceasing of external excitation. More importantly, NIR self-sustained luminescence can be triggered by wideband irradiation with ultraviolet to visible light over 230–550 nm. As expected, 365 nm UV lamp, natural sunlight and LED flash can all effectively charge these NIR persistent phosphors and induce commendable NIR persistent luminescence performance. Considering the invisibility of NIR emission to the naked eye, very broad persistent luminescence excitation band, and long-lasting NIR luminescence after excitation, these Bi2+-activated NIR persistent phosphors are expected to find important applications in optical information storage and anti-counterfeiting fields.

Intelligent model to image enrichment for strong night-vision surveillance cameras in future generation

Intelligent model to image enrichment for strong night-vision surveillance cameras in future generation

Near infrared emitting Cr3+ doped Zn3Ga2Ge2O10 long persistent phosphor for night vision surveillance and anti-counterfeit applications

The Cr3+ doped Zn3Ga2Ge2O10 long persistent phosphor materials were synthesized by solid state reaction method. The crystal structure of the synthesized phosphors are cubic with space group Fd3m. The band gap of the undoped host is about 4.48 eV. The materials show three photoluminescence excitation bands peaked at 260 nm, 412 nm and 580 nm. Due to the broad excitation band, the phosphors can be excited by UV light or visible light or sunlight. The phosphors shows a photoluminescence emission band peaked at 698 nm when excited by UV light. The afterglow emission shows a broad emission band with maximum at 700 nm. The detection of NIR light from the sample was observed by Night Vision Monocular for 24 h after switch off the excitation source. A mechanism is introduced to describe afterglow phenomenon and trap depth was calculated from thermoluminescence curve. As the material emit NIR persistent light, it was used as a secret light source for night vision devices. The developed material was used for tagging, tracking and locating purposes in defence application. The acrylic based paint was prepared to develop long persistent near infrared (NIR) paint, which can be coated on combat vehicle, ship, weapon, helmet, cloth, tent, rock for defence application. The NIR security ink was prepared and demonstrated to prevent counterfeit. Encryption and decryption method of confidential information was presented by using NIR security ink.

Broadband Short-Wave Infrared Light-Emitting Diodes Based on Cr3+-Doped LiScGeO4 Phosphor

Short-wave infrared (SWIR) spectroscopy has recently emerged as an important technology across a wide range of areas, whether industrial, biomedical, or environmental. Nevertheless, it is still a long-standing challenge to develop robust SWIR light sources. The SWIR phosphor-convert light emitting diodes (LEDs) by coating blue LED chips with desirable SWIR-emitting phosphors are becoming an ideal alternative for solid-state SWIR light sources due to its compactness, low-cost, and long operating lifetime, as does the commercial white LEDs. Herein, we report a blue-pumped Cr3+-doped LiScGeO4 SWIR phosphor as a luminescent converter for phosphor-convert SWIR LEDs. This phosphor shows an intense SWIR emission band with a peak wavelength at ∼1120 nm owing to the 4T2 → 4A2 electron transition of Cr3+ when exciting with blue light. The full width at half-maximum (fwhm) of the phosphor is ∼300 nm and the absolute quantum efficiency is determined to be ∼26%. SWIR LED prototypes are constructed by combining the optimized phosphor materials with commercial blue InGaN LED chips, which can generate a commendable emission band in the SWIR region over 800-1600 nm and achieve a maximum output power of ∼4.78 mW at 60 mA with the photoconversion efficiency of 4.4%. The current exploration of Cr3+-doped SWIR-emitting phosphors will lay the foundation to engineer phosphor-convert SWIR LEDs for applications in night-vision surveillance and SWIR spectroscopy technology. These blue-light-excitable SWIR-emitting phosphors can serve as an important complement to the spectral gap of the current Cr3+-doped phosphors in the SWIR region and will pave the way toward cost-effective phosphor-converted solid-state SWIR light sources.

Enhanced near-infrared persistent luminescence in MgGa2O4:Cr3+ through codoping

Near-infrared emitting persistent luminescent materials have potential applications in night-vision surveillance and medical imaging. Rational designing of the phosphor composition is of great importance for achieving sufficiently strong and long-lasting persistent luminescence. Herein, a series of MgGa2O4:Cr3+ phosphors with variable concentrations of Cr3+ were prepared via solid state reaction. MgGa2O4:Cr3+ exhibits strong emission in the range from 650 to 800 nm and three excitation bands centered at 275, 420 and 576 nm. With appropriate selection of codopant M (M = Al3+, Si4+, Ge4+ or Sn4+), the MgGa2O4:Cr3+, M phosphor presents remarkably enhanced persistent luminescence. Moreover, the trap distributions were tuned and the number of traps was greatly increased via codoping. In particular, MgGa2O4:Cr3+, Si4+ shows more than 7 h of persistent near-infrared light emission before the intensity drops to 5 × 10−4 mWsr−1m−2. Codoping with appropriate ions provides a good example in optimization and development of persistent luminescent phosphors for potential bioimaging applications.

A new persistent blue-emitting phosphor: Tailoring the trap density for enhancing the persistent time

In recent times, non-Eu2+ based persistent phosphor materials show promise for self-sustained night vision surveillance and bio-imaging owing to their ability to luminesce overnight, high chemical stability, and broad-band absorption. While green and yellow wavelengths are widely explored, the research and development of persistent phosphors in the blue region are still lacking, owing to the limited understanding of the luminescence persistence mechanism. Herein, it is to be reported a new blue-emitting Na3ScSi3O9:Ce3+, Dy3+ phosphor, which exhibits a strong emission at 450 nm that persists for nearly 17 h above the recognizable intensity level (0.32 mcd/m2), which is the longest persistent phosphor in the blue region. Thermoluminescence experiments reveal a fifth-order-of-magnitude rise in the trap density by Dy3+ incorporation into Na3ScSi3O9:Ce3+, which is responsible for the long persistence of the emission. Furthermore, by employing Mn2+, Tb3+, and Dy3+ as co-activators, it is realized that the trap density is proportional to the persistence time. Finally, an underlying mechanism for this blue emission persistence is proposed. These results might push forward the design of new blue-emitting phosphors with higher persistent luminescence efficiencies.

Facile Synthesis of Mn4+-Activated Double Perovskite Germanate Phosphors with Near-Infrared Persistent Luminescence.

Tetravalent manganese doped phosphors are emerging as a new class of efficient near-infrared emitters for applications in a variety of areas, such as bioimaging and night-vision surveillance. Novel double perovskite-type La2MgGeO6:Mn4+ phosphors were successfully prepared using a microwave-assisted energy-saving solid state method. This simple technique involving the use of a microwave susceptor allows for a reduction of the preparation time compared to a conventional solid state reaction. The samples were investigated using powder X-ray diffraction, scanning electron microscopy, as well as energy-dispersive X-ray spectroscopy mapping, photoluminescence excitation/emission spectroscopy, persistent luminescence decay and temperature-dependent photoluminescence analysis. Substitution between isovalent Mn4+ and Ge4+ can be achieved without additional charge compensators in this germanate-based phosphor, which provides strong emission in the near-infrared spectral region, assigned to the characteristic transitions of tetravalent manganese ions. Additionally, the double perovskite-type germanate phosphor exhibits excellent luminescence thermal stability. Moreover, the spectroscopic properties, excitation wavelength-dependent and temperature-dependent persistent luminescence were studied. A series of thermoluminescence measurements were presented trying to give clear information on the charging process, afterglow behavior and the nature of the traps responsible for the persistent luminescence. The present investigation expands the range of available promising near-infrared emitting persistent phosphors for medical imaging.

Performance Analysis of Illumination Invariant Change Detection Method for Detecting Image Change in Night Vision Camera

At present, the use of video cameras is not only limited to documenting events but is also used for surveillance systems. Changes in lighting that occur in the surveillance area is one of the problems that result in a false alarm on the surveillance system. Illumination Invariant Change Detection is a method for detecting image changes on images. This study aims to determine the performance of the Illumination Invariant Change Detection method to detect image changes in night vision surveillance cameras. The Illumination Invariant Change Detection method does not work well for detecting image changes on a night vision camera under dark lighting conditions at an average value of Lux 0 with an infrared lamp on. The accuracy of the application of the method to detect image changes on night vision cameras is 80% with the selection of the threshold value of the detection of image changes that is 75000 pixels.

Infrared and visible image fusion using structure-transferring fusion method

It is commonly believed that the purpose of the image fusion is to merge as much information, such as contour, texture and intensity distribution information from original images, as possible into the fusion image. Most of the existing methods treat different source images equally with certain feature extracting operation during the fusion process. However, as for the infrared (IR) and visible image fusion problem, the features of images taken from two imaging devices with different sensitive wave bands are different, sometimes even adverse. We can’t extract and preserve the opposite information at the same time. To keep the targets salient in clutter background and visual friendly, in this paper, a novel IR and visible image fusion method called structure transferring fusion method (STF) is first proposed. Firstly, the structure-transferring model is built to transfer the grayscale structure from the visible input image into the IR image. Secondly, infrared detail enhancing strategy is carried out to supplement the missing details of the IR image. Experimental results reveal that the proposed STF method is both effective and efficient for IR and visible image fusion. The final fusion image with conspicuous targets and vivid texture is conducive to night vision surveillance for human observers.

Sr2MgWO6:Cr3+ phosphors with effective near-infrared fluorescence and long-lasting phosphorescence

Cr3+-doped near-infrared (NIR) long-lasting phosphorescence (LLP) phosphors have drawn great attention for the promising application in unique bio-labels. Most of the studies are focused on gallate materials. Here we report a novel non-gallates NIR LLP phosphor Sr2MgWO6:Cr3+ that exhibit broadband emission at 700–1000 nm. X-ray powder diffraction, photoluminescence spectra, photoluminescence excitation spectra, LLP decay curves and thermoluminescence glow curves were determined to study the NIR LLP property and mechanism of Sr2MgWO6:Cr3+. Although Sr2MgWO6:0.4%Cr3+ gives the strongest NIR emission, the optimum content of Cr3+ in Sr2MgWO6 phosphor for LLP was 0.1%. Trap type and depth in Sr2MgWO6:Cr3+ were also discussed according to the thermoluminescence glow curves. Sr2MgWO6:Cr3+ phosphor is promising in optical information storage, night-vision surveillance, and in vivo bio-imaging.