A nonparametric point-by-point method to measure time-dependent frequency in wavelength modulation spectroscopy.

A nonparametric point-by-point (NPP) method is presented for high-accuracy measurement of the time-dependent frequency (laser frequency) in tunable laser absorption spectroscopy, crucial for ensuring ultimate measurement accuracy. In wavelength modulation spectroscopy in particular, the parametric methods in current use for time-dependent frequency measurement are insufficiently accurate and are difficult to apply to complex modulation scenarios. Based on a multi-scale viewpoint, point-by-point measurement of the frequency is realized by linear superposition of the frequency information mapped from the interferometric signal on a unit scale and on a local scale. Validation experiments indicate that the measurement accuracy of the proposed NPP method is three times that of the existing parametric methods, while effectively immunizing against non-ideal tuning effects. Additionally, the NPP method is suitable for use with arbitrarily complex modulations such as square wave modulation, for which parametric methods are inapplicable.

Calibration-free infrared absorption spectroscopy using cantilever-enhanced photoacoustic detection of the optical power.

We report on sensitive tunable laser absorption spectroscopy using a multipass gas cell and a solid-state photoacoustic optical power detector. Unlike photoacoustic spectroscopy (PAS), this method readily allows a low gas pressure for high spectral selectivity and a free gas flow for continuous measurements. Our photoacoustic optical power detector has a large linear dynamic range and can be used at almost any optical wavelength, including the middle infrared and THz regions that are challenging to cover with traditional optical detectors. Furthermore, our approach allows for compensation of laser power drifts with a single detector. As a proof of concept, we have measured very weak CO2 absorption lines at 9.2 µm wavelength and achieved a normalized noise equivalent absorption (NNEA) of 2.35·10-9 Wcm-1Hz-1/2 with a low-power quantum cascade laser. The absolute value of the gas absorption coefficient is obtained directly from the Beer-Lambert law, making the technique calibration-free.

Suppression of cross-interference in the absorption spectra of gas mixtures.

In the quantitative analysis of mixed gases by tunable diode laser absorption spectroscopy, the overlapping of absorption spectra and mutual interference of multi-component gases can lead to problems of large measurement errors and low analysis accuracy. In this paper, an improved firefly algorithm is proposed and applied to the support vector machine regression model to solve this problem. The specific method includes introducing an adaptive step size to balance the local and global searches and using the gradient descent method to accelerate the parameter optimization process so as to improve the model's generalization ability and prediction accuracy. The experimental results show that the maximum errors of the improved algorithm in the prediction of CH4 and CO gas concentrations are no more than 0.0443 % and 2 ppm, with coefficients of determination, R2, of 0.9994 and 0.99815. The promising results obtained by the system provide theoretical support for the realization of high-precision detection of multicomponent gases with a single source of light, and also demonstrate the high efficiency and feasibility of the method in practical detection.

Cohesive Living Bacterial Films with Tunable Mechanical Properties from Cell Surface Protein Display.

Engineered living materials (ELMs) constitute a novel class of functional materials that contain living organisms. The mechanical properties of many such systems are dominated by the polymeric matrices used to encapsulate the cellular components of the material, making it hard to tune the mechanical behavior through genetic manipulation. To address this issue, we have developed living materials in which mechanical properties are controlled by the cell-surface display of engineered proteins. Here, we show that engineered Esherichia coli cells outfitted with surface-displayed elastin-like proteins (ELPs, designated E6) grow into soft, cohesive bacterial films with biaxial moduli around 14 kPa. When subjected to bulge-testing, such films yielded at strains of approximately 10%. Introduction of a single cysteine residue near the exposed N-terminus of the ELP (to afford a protein designated CE6) increases the film modulus 3-fold to 44 kPa and eliminates the yielding behavior. When subjected to oscillatory stress, films prepared from E. coli strains bearing CE6 exhibit modest hysteresis and full strain recovery; in E6 films much more significant hysteresis and substantial plastic deformation are observed. CE6 films heal autonomously after damage, with the biaxial modulus fully restored after a few hours. This work establishes an approach to living materials with genetically programmable mechanical properties and a capacity for self-healing. Such materials may find application in biomanufacturing, biosensing, and bioremediation.

IMPMH, direct tunable diode laser absorption spectroscopy for detection of water vapour under "Optically thick Condition".

Water vapour plays a crucial role in atmospheric processes. Hence, monitoring the altitude-related variations in water vapour properties is important to decipher atmospheric processes. Direct tunable diode laser absorption spectroscopy (dTDLAS) measures the concentration and temperature of gas molecules by scanning the rotation-vibration absorption lines using a high-spectral-resolution laser. In this study, we devised an integrated measurement and data processing method (integrative measurement and processing method for hygrometry, IMPMH) to enhance the in-situ airborne measurement capability of dTDLAS. We measured a wide range (240-18,000 ppm) of water vapour concentrations, aiming for atmospheric measurements in a highly water-saturated regime, called the "optically thick condition". For recovering the full absorption spectra, the "integrative area" was defined and a difference factor D, which is the distance between two spectral regions with width corresponding to the half width of half maximum of the Voigt profile, was used to calculate the area. From the data, the low-bound concentration was measured to be 244 ppm. At D = 1.8, the transition concentration to the "optically thick condition" was measured to be 5,800 ppm. By increasing D from 1.8 to 2.8, the measurable upper-bound concentration increased to 17,993 ppm. IMPMH was applied to the measured data to estimate the final absorber density or water vapour concentration. The estimation was well-fitted with the measured detector signal with signal-to-noise ratio (SNR) of âˆ¼ 300 of the residual spectrum, promising its applicability to in-situ airborne measurements. To validate IMPMH, the water vapour concentration range was divided into two regimes: (1) optically thick (5,800 < c < 18,000 ppm) and (2) optically thin (c < 5,800 ppm) conditions. Under the optically thick condition, IMPMH was validated by comparing the results between the short and long-path cells. In the optically thin condition, IMPMH was validated through comparison with the general dTDLAS method. Lastly, long-term stability of the dTDLAS system was validated by measuring 10 different concentrations (240-18,000 ppm) for 1000 s by characterising the precision and SNRs of the residual. The results demonstrate that IMPMH significantly enhances the in-situ airborne measurement capability of dTDLAS under both optically thick and thin conditions. Furthermore, requirements for the implementation of IMPMH in airborne measurement were investigated considering four aspects-sampling, low-pressure measurement, accuracy and precision, and multiplex detection. The results were examined with regard to atmospheric implications.

Color Tunable Three Terminal (3-T) Vertically Stacked Tandem Organic Electroluminescent Devices.

Traditional full-color displays typically use a pixel layout with three side-by-side subpixels emitting red (R), green (G), and blue (B) colors. However, this configuration limits the resolution especially in augmented reality (AR) and virtual reality (VR) applications. To address the issue of low pixel density in display technology, this study demonstrated vertically stacked three-terminal (3-T) bottom-emitting tandem OLEDs (sOLED). These OLEDs offer color tunability, facilitated by individually controlled colour units. This study demonstrates two combinations: G+B and R+G. Incorporating three generations of OLED's materials phosphorescent (R), thermally activated delayed fluorescence (TADF) (G), and hyperfluorescent (B). The OLEDs achieve maximum current efficiencies of approximately 11 cd/A, 52.4 cd/A, and 40.7 cd/A for R, G, and B, respectively, in their respective tandem configurations. A wide range of colors can be achieved by blending G+B and R+G color spectrum by adjusting the voltage of independent color unit. The optimal mix results in a fine cyan color with CIE coordinates (0.273,0.5) in G+B sOLED and a warm white with CIE coordinates (0.416,0.518)in R+G sOLED. This work demonstrate a better performing 3-T sOLED utilizing three different generations OLED materials, offering an individual control within a single pixel providing enhanced pixel density for display technology.

Flexible Piezoelectric Nanocolumnar Composite Films as Flat-Panel Loudspeakers: Application and Modeling.

Highly anisotropic piezoelectric composites promise to progress electroacoustic devices as a class by combining the advantages of both piezoceramics and polymers. Fundamentally, piezoelectric loudspeakers employ the converse piezoelectric effect to convert electrical to mechanical energy. Quasi-1-3 piezoceramic/polymer composites enable flat-panel loudspeakers that are tunable in elastic modulus, with opportunities for mechanical flexibility, optical transparency, and large-area coverage. Their processing route enables relatively flexible design parameters, such as the particle loading, polymer-matrix modulus, film thickness, film size, and electrode-material stiffness. Alternative processing routes of electric field (E-field) aligned-piezoelectric composites are demonstrated, including using the relaxor ferroelectric lead magnesium niobate-lead titanate (PMN-PT) to enhance the acoustic performance and photocurable resins to accelerate the materials processing. Material properties critical for dielectrophoresis are characterized, and loudspeakers were fabricated based on the optimal processing conditions. Subsequently, electroacoustic characterization explores the effect of loudspeaker size, substrate stiffness, the microphone distance, the piezoceramic material, and the matrix modulus. Finally, finite-element (FE) modeling of the electromechanical behavior validates the natural frequencies and modes shapes of the loudspeakers via the analytical solution and frequency response to electrical and mechanical excitation. Good correspondence between the predicted electroacoustic performance and experimentally validated model is observed.

Dressing AgNWs with MXenes Nanosheets: Transparent Printed Electrodes Combining High-Conductivity and Tunable Work Function for High-Performance Opto-Electronics.

High-work function transparent electrodes (HWFTEs) are key for establishing Schottky and Ohmic contacts with n-type and p-type semiconductors, respectively. However, the development of printable materials that combine high transmittance, low sheet resistance, and tunable work function remains an outstanding challenge. This work reports a high-performance HWFTE composed of Ag nanowires enveloped conformally by Ti3C2Tx nanosheets (TA), forming a shell-core network structure. The printed TA HWFTEs display an ultrahigh transmittance (>94%) from the deep-ultraviolet (DUV) to the entire visible spectral region, a low sheet resistance (<15 Ω sq-1), and a tunable work function ranging from 4.7 to 6.0 eV. The introduction of additional oxygen terminations on the Ti3C2Tx surface generates positive dipoles, which not only increases the work function of the TA HWFTEs but also elevates the TA/Ga2O3 Schottky barrier, resulting in a high self-powered responsivity of 18 mA W-1 in Ga2O3 diode DUV photodetectors, as demonstrated via experimental characterizations and theoretical calculations. Furthermore, the TA HWFTEs-based organic light-emitting transistors exhibit exceptional emission brightness of 5020 cd m-2, being four-fold greater than that in Au electrodes-based devices. The innovative nano-structure design, work function tuning, and the revealed mechanisms of electrode-semiconductor contact physics constitute a substantial advancement in high-performance optoelectronic technology.

Dynamic Wavelength-Selective Diffraction and Absorption with Direct-Patterned Hydrogel Metagrating.

Hydrogel nanophotonic devices exhibit attractive tunable capabilities in structural coloration and optical display. However, current hydrogel-based tunable strategies are mostly based on a single physical mechanism, and it remains a challenge to merge multiple mechanisms for active devices with integrated functionalities. Here, a hydrogel metagrating combining Fabry-Pérot (FP) resonance and diffraction effects is proposed for achieving tunable absorption and dynamic wavelength-selective beam steering. Through exploiting hydrogel shrinkage under electron-beam exposure, a hydrogel nanocavity composed of Ag/Hydrogel/Ag three-layer films can be directly printed with arbitrary patterns, enabling the direct-pattering technique of metagrating. The hydrogel nanocavity performs as an FP-type absorber, and its absorption peak rapidly shifts with humidity variation due to the hydrogel layer scaling. The response speed is <320 ms, and the absorption peak shift range is >150 nm. It is further demonstrated that the hydrogel metagrating exclusively deflects light at the resonance wavelength, and its operating wavelength can be actively switched by regulating ambient humidity. The proposed tunable hydrogel metagrating can promote new technologies of tunable metasurfaces for optical filtering, gas sensing, and optical imaging.

Effects of Salt Concentration on a Magnetic Nanoparticle-Based Aggregation Assay with a Tunable Dynamic Range.

Magnetic nanoparticles (MNPs) can be functionalized with antibodies to give them an affinity for a biomarker of interest. Functionalized MNPs (fMNPs) cluster in the presence of a multivalent target, causing a change in their magnetization. Target concentration can be proportional to the 3rd harmonic phase of the fMNP magnetization signal. fMNP clustering can also be induced with salt. Generally, salt can alter the stability of charge stabilized fMNPs causing a change in magnetization that is not proportional to the target concentration. We have developed a model system consisting of biotinylated MNPs (biotin-MNPs) that target streptavidin to study the effects of salt concentration on fMNP-based biosensing in simulated in vivo conditions. We have found that biotin-MNP streptavidin targeting was independent of salt concentration for 0.005x to 1.00x phosphate buffered saline (PBS) solutions. Additionally, we show that our biosensor's measurable concentration range (dynamic range) can be tuned with biotin density. Our results can be leveraged to design an in vivo nanoparticle (NP)-based biosensor with enhanced efficacy in the event of varying salt concentrations.

Functional Carbon Springs Enabled Dynamic Tunable Microwave Absorption and Thermal Insulation.

Electromagnetic (EM) wave pollution and thermal damage pose serious hazards to delicate instruments. Functional aerogels offer a promising solution by mitigating EM interference and isolating heat. However, most of these materials struggle to balance thermal protection with microwave absorption (MA) efficiency due to a previously unidentified conflict between the optimizing strategies of the two properties. Herein, this study reports a solution involving the design of a carbon-based aerogel called functional carbon spring (FCS). Its unique long-range lamellar multi-arch microstructure enables tunable MA performance and excellent thermal insulation capability. Adjusting compression strain from 0% to 50%, the adjustable effective absorption bandwidth (EAB) spans up to 13.4 GHz, covering 84% of the measured frequency spectrum. Notably, at 75% strain, the EAB drops to 0 GHz, demonstrating a novel "on-off" switchability for MA performance. Its ultralow vertical thermal conductivity (12.7 mW m-1 K-1) and unique anisotropic heat transfer mechanism endow FCS with superior thermal protection effectiveness. Numerical simulations demonstrate that FCS outperforms common honeycomb structures and isotropic porous aerogels in thermal management. Furthermore, an "electromagnetic-thermal" dual-protection material database is established, which intuitively demonstrates the superiority of the solution. This work contributes to the advancement of multifunctional MA materials with significant potential for practical applications.

Hydroxypropyl Cellulose-Based Meter-Long Structurally Colored Fibers for Advanced Fabrics.

Structurally colored fibers are attractive alternatives to chemically colored fibers due to their rich optical properties, color stability, and environmental friendliness. However, the fabrication of structurally colored fibers using cost-effective raw materials with the possibility to scale up remains challenging. Here, a simple and scalable approach is developed to fabricate continuous meter-long structurally colored fibers exhibiting brilliant structural colors across the visible spectrum and helix orientation-dependent polarization states. The fibers are fabricated by extrusion of concentrated aqueous solutions of chemically crosslinked hydroxypropyl cellulose (HPC). The wavelengths and polarization states can be tuned by solution concentration, relaxation time, and collector's surface energy. The HPC-based structurally colored fibers display excellent optical stability to mechanical straining, repeated drying/water impregnation, and prolonged heating at 150 °C. It is demonstrated that the HPC-based structurally colored fibers can be woven into structurally colored fabrics with wavelength- and polarization-coded optical patterns. The current work presents a strategy to tune the chiral nematic order, which constitutes an important step toward mass production of structurally colored fibers with stable and rich optical properties using easily available raw materials.

Geometric mechanics of kiri-origami-based bifurcated mechanical metamaterials.

We explore a new design strategy of leveraging kinematic bifurcation in creating origami/kirigami-based three-dimensional (3D) hierarchical, reconfigurable, mechanical metamaterials with tunable mechanical responses. We start from constructing three basic, thick, panel-based structural units composed of 4, 6 and 8 rigidly rotatable cubes in close-looped connections. They are modelled, respectively, as 4R, 6R and 8R (R stands for revolute joint) spatial looped kinematic mechanisms, and are used to create a library of reconfigurable hierarchical building blocks that exhibit kinematic bifurcations. We analytically investigate their reconfiguration kinematics and predict the occurrence and locations of kinematic bifurcations through a trial-correction modelling method. These building blocks are tessellated in 3D to create various 3D bifurcated hierarchical mechanical metamaterials that preserve the kinematic bifurcations in their building blocks to reconfigure into different 3D architectures. By combining the kinematics and considering the elastic torsional energy stored in the folds, we develop the geometric mechanics to predict their tunable anisotropic Poisson's ratios and stiffnesses. We find that kinematic bifurcation can significantly effect mechanical responses, including changing the sign of Poisson's ratios from negative to positive beyond bifurcation, tuning the anisotropy, and overcoming the polarity of structural stiffness and enhancing the number of deformation paths with more reconfigured shapes.This article is part of the theme issue 'Origami/Kirigami-inspired structures: from fundamentals to applications'.

All-In-One Optoelectronic Transistors for Bio-Inspired Visual System.

Visual perception has profound effects on human decision-making and emotional responses. Replicating the functions of the human visual system through device development has been a constant pursuit in recent years. However, to fully simulate the various functions of the human visual system, it is often necessary to integrate multiple devices with different functions, resulting in complex, large-volume device structures and increased power consumption. Here, an optoelectronic transistor with comprehensive visual functions is introduced. By coupling diverse photoreceptive properties of the channel and electrical regulation through charge injection/ferroelectric switching from the hafnium-based gate, the devices can simulate functions of both photoreceptors in the retina and synapses in the visual cortex. A device array is constructed to confirm the perceptual functions of cone and rod cells. Subsequently, color discrimination and recognition for color images are achieved by combining the tunable perception and synapse functions. Then an intelligent traffic judgment system with this all-in-one device is developed, which is capable of making judgments and decisions regarding traffic signals and pedestrian movements. This work provides a potential solution for developing compact and efficient devices for the next-generation bio-inspired visual system.

A Dynamic H-Bonding Network Enables Stimuli-Responsive Color-Tunable Chiral Afterglow Polymer for 4D Encryption.

The development of stimuli-responsive and color-tunable chiral organic afterglow materials has attracted great attention but remains a daunting challenge. Here, a simple yet effective strategy through the construction of a dynamic H-bonding network is proposed to explore the multi-color stimuli-responsive chiral afterglow by doping a self-designed chiral phosphorescent chromophore into a polyvinyl alcohol matrix. A stimuli-responsive deep blue chiral afterglow system with a lifetime of up to 3.35 s, quantum yield of 25.0%, and luminescent dissymmetry factor of up to 0.05 is achieved through reversible formation and breakdown of the H-bonding network upon thermal-heating and water-fumigating. Moreover, multi-color stimuli-responsive chiral afterglow can be obtained by chiral and afterglow energy transfer, allowing the establishment of afterglow information displays and high-level 4D encryption. This work not only offers a facile platform to develop advanced stimuli-responsive materials but also opens a new avenue for developing next-generation optical information technology with enhanced functionality and responsiveness.

Light-Controlled Magnetic Properties: An Energy-Efficient Opto-Mechanical Control over Magnetic Films by Liquid Crystalline Networks.

Magnetostrictive materials are essential components in sensors, actuators, and energy-storage devices due to their ability to convert mechanical stress into changes in magnetic properties and vice-versa. However, their operation typically requires physical contact to apply stress or relies on magnetic field sources to control magnetic properties. This poses significant limitations to devices miniaturization and their integration into contactless technologies. This work reports on an approach that overcomes these limitations by using light to transfer mechanical stress to a magnetostrictive device, thereby achieving non-contact and reversible opto-mechanical control of its magnetic and electrical properties. The proposed solution combines a magnetostrictive Fe70Ga30 thin film with a photo-responsive Liquid Crystalline Network (LCN). Magnetic properties are modulated by changing the light wavelength and illumination time. Remarkably, the stable shape change of the LCN induced by ultraviolet (UV) light leads to the retention of magnetic properties even after the light is switched off, resulting in a magnetic memory effect with an energy consumption advantage over the use of conventional magnetic field applicators. The memory effect is erased by visible light, which releases the mechanical stress in the photoresponsive layer. Therefore, this new composite material creates a fully reconfigurable magnetic system controlled by light.

Nanoarchitectonics of tunable aminosalicylate sodium encapsulated gold nanoparticles enabling multi-faceted role as capping, reducing, stabilizing and colorimetric detection of metal ions.

Despite all the advancements in aqueous synthesis of gold nanoparticles, certain features like one-pot/one-step method with minimal reactants using greener solvents are still demanding. The challenge in the aqueous phase synthesis is to balance the nucleation and precise growth of nanoparticles avoiding aggregation. In this work, we report a unique versatile unexplored molecule aminosalicylate sodium (Na-4-ASA) which functions as a capping, reducing, stabilizing and more interestingly as an encapsulating agent for gold nanoparticles. This multi-faceted molecule showed excellent control in synthesizing monodisperse tunable encapsulated nanoparticles of sizes (60 nm, 53 nm and 12 nm) exhibiting absorbance bands at 560 nm, 540 nm and 520 nm respectively. X-ray diffraction and Fourier Transmission Infra-Red validated crystalline structure and binding of Na-4-ASA onto gold nanoparticles surface respectively. Furthermore, the AuNPs were investigated for their ability to detect metal ions through colorimetric change where purification via centrifugation turned out to be a key parameter in enabling the detection. Selectivity towards Al3+was observed with the 12 nm sized nanoparticles at 0.5 ppm metal ion concentration. The AuNPs of sizes 60 nm and 53 nm detected Al3+/Cr3+/Fe3+and Al3+/Fe3+respectively indicating the impact of size in heavy metal ions detection. The greater the size of AuNPs, lower is the selectivity where detection of three metal ions were observed and vice versa i.e. smaller-sized AuNPs showed high selectivity by detecting single metal ion. Also, the time duration for detection increased with decreasing size of the AuNPs. Finally, LOD for the heavy metal ions Al3+, Cr3+, and Fe3+were calculated as 67 ppb, 78 ppb, 76 ppb respectively.

Polarization Independent Dynamic Beam Steering based on Liquid Crystal Integrated Metasurface.

Digital Micromirror Devices, extensively employed in projection displays offer rapid, polarization-independent beam steering. However, they are constrained by microelectromechanical system limitations, resulting in reduced resolution, limited beam steering angle and poor stability, which hinder further performance optimization. Liquid Crystal on Silicon technology, employing liquid crystal (LC) and silicon chip technology, with properties of high resolution, high contrast and good stability. Nevertheless, its polarization-dependent issues lead to complex system and low efficiency in device applications. This paper introduces a hybrid integration of metallic metasurface with nematic LC, facilitating a polarization-independent beam steering device capable of large-angle deflections. Employing principles of geometrical phase and plasmonic resonances, the metallic metasurface, coupled with an electronically controlled LC, allows for dynamic adjustment, achieving a maximum deflection of ± 27.1°. Additionally, the integration of an LC-infused dielectric grating for dynamic phase modulation and the metasurface for polarization conversion ensures uniform modulation effects across all polarizations within the device. We verify the device's large-angle beam deflection capability and polarization insensitivity effect in simulations and propose an optimization scheme to cope with the low efficiency of individual diffraction stages.

Color-Tunable Lead Halide Perovskite Single-Mode Chiral Microlasers with Exceptionally High glum.

Chiral microlasers hold great promise for optoelectronics from integrated photonic devices to high-density quantum information processing. Despite significant progress in lead-halide perovskite emitters, chiral lasing with high dissymmetry factors (glum) has not yet been realized. Here, we demonstrate chiral single-mode microlasers with exceptional stability and tunable emission across the visible range by combining CsPbClxBr3-x perovskite microrods (MRs) with a cholesteric liquid crystal (CLC) layer. The MRs lase via a whispering gallery mode (WGM) microcavity and confer chirality through the encapsulated CLC layer, thus exhibiting circularly polarized lasing with dissymmetry factors reaching 1.62. Importantly, we demonstrate wavelength-tunable high dissymmetry chiral lasers in a broad spectral range by tuning the halide composition and using CLC layers with the desired photonic bandgap (PBG). This facile approach to generate chiral lasing not only is applicable to semiconductor nano- and microcrystals but also paves the way for potential integration into nanoscale photonic devices.

Excitation wavelength and time dependent colour tunable room temperature phosphorescence from boron doped carbon nanodots.

Developing metal free room temperature phosphorescence (RTP) materials have received tremendous attention due its potential application in various fields such as sensing, optoelectronics and anticounterfeiting. Herein, we have synthesized an excitation wavelength and time dependent phosphorescent boron doped carbon nanodots (BCNDs) by thermal treatment of ethanolamine and boric acid at 240 °C, where boric acid act as both doping and host agents. The obtained BCNDs display blue to orange fluorescence in both aqueous medium and solid state. In addition, the BCNDs display tunable orange-yellow-green phosphorescence in solid state under UV and visible light, lasting upto 10 s, visible to naked eye. The boron and nitrogen doping regulates the band gap of the BCNDs, resulting the phosphorescence colour tunability. The average phosphorescence lifetime and quantum yield of BCNDs are found to be 1.27 s and 8.61% respectively. Based on the optical properties, the BCNDs are applied as security ink in information encryption and security marking. Hence, this work can promote the development of metal free phosphorescent carbon based materials which may find application in various emerging fields.