- SJ_Zhang
- Jul. 7, 2025
Abstract
Directional light source not only helps to advance scientific progresses but also has great potentials in many application fields. However, it is still challenging to achieve the directional white light without optical elements. Here, we report a highly directional white-light emitter driven by 1064 nm near-infrared laser with 1/60 solid angle that does not require the introduction of optical elements. The emitter which consists of binary components, i.e. carbon dot and titanium oxide, possesses a microlens-shape surface formed during the synthesis process. Upon near-infrared light excitation, carbon dot emits white light based on a fundamentally different mechanism, which may involve a process similar to bremsstrahlung, multiphoton and thermal processes. The emitted white light is then regulated in the near field by the microlens-shape surface due to the confinement effect, resulting in the high directionality. The highly directional white-light emitter exhibits excellent stability and repeatability, making it promising for applications including targeted illumination and projection.
Introduction
White-light technologies have penetrated billions of households deeply, enhancing visibility, safety and ambiance in homes, offices and public spaces1,2,3. The well-managed lighting has a profound influence on our everyday life, contributing to overall well-being and productivity. Up till now, a variety of white-light sources which include incandescent lightbulbs, fluorescent lamps and light-emitting diode have been developed and utilized under different circumstances, such as general illumination4,5,6,7, communication8,9, sensing10,11, imaging12,13 and healthcare14,15. Among others, due to the green and energy-saving natures which originate from the long lifetime and low driving voltage, white light generated by monochromatic sources has achieved remarkable successes and is believed to be indispensable as the next generation light sources16,17,18,19,20,21,22,23. Such white-light sources normally feature the Lambertian emission which lay the foundation of their applications in lighting and display fields.
On the other hand, there is an enormous demand for directional white-light sources which have wide applications in the fields of targeted illumination and projection24,25,26. The directional light can minimize glare in case of automotive headlights by reducing the illumination cone, increase visibility in case of accent lighting or comprise core illumination components in the case of scientific instruments. In order to achieve the desired directionality out of the Lambertian white-light source, various bulky optical elements ranging from lenses, mirrors to reflectors and optical fibers are inevitably required27,28,29,30,31. With the aids of these optical elements, the Lambertian emissions could thus be shaped into light beams with decreased solid angles through reflection, refraction, or their combinations. However, the limitations in the sizes of light sources, energy requirements as well as price have posed great hinderances on their practical applications. It still remains a challenge to realize directional white light without the introduction of optical elements.
In this paper, we report a white-light emitter, which emits highly directional white light (with a solid angle of 1/60) excited by monochromatic 1064 nm near-infrared (NIR) laser in the absence of optical elements (Fig. 1a). The emitter consists of binary constituents, i.e. carbon dot (CDot) and titanium dioxide (TiO2), which function as the center of light emission and stabilizer, respectively. Under NIR light, CDots emit white light based on a fundamentally different mechanism that may combine a process similar to bremsstrahlung, multiphoton and thermal processes. The directionality derives from the confinement effect of the microlens-shape surface formed during the synthesis process, which is capable of regulating the white light emitted by CDots in the near field into a highly directional one. The highly directional feature, together with the excellent stability and repeatability, makes the white-light emitter in the current study attractive for a variety of practical fields. As a proof-of-concept, we have demonstrated its potential in the fields of targeted illumination and projection.
Fig. 1: Schematic illustration showing the directional white light and the characterization of the emitter.
a Schematic of the directional white-light emission from the emitter under NIR excitation. b Cross-sectional scanning electron microscope (SEM) image indicating the microlens-shape surface and the sintered interior of the emitter consisting of the CDot-TiO2 composite (orange dashed rectangle highlights the sintered interior). c The enlarged image showing the surface structure of the CDot-TiO2 composite. d Transmission electron microscope (TEM) image of the CDot-TiO2 composite. e High-resolution TEM image showing CDot and TiO2 domains inside the green dashed square marked in (d). The corresponding fast Fourier transform (FFT) patterns of TiO2 and CDot are shown in (f) and (g), respectively. h X-ray diffraction (XRD) of the CDot-TiO2 composite. Black lines are the standard peaks of rutile TiO2 (JCPDS NO. 21-1276).
Results
Characterization of the white-light emitter
The emitter is composed of the CDot-TiO2 composite (Supplementary Fig. 1) which is synthesized by the laser heating method (see Supplementary Fig. 2 and the fabrication methods section for details). During laser heating, the CDot and TiO2NP composite that is subject to the laser irradiation (10 W/cm2 1064 nm laser for 2 s) experiences a temperature rise because of the photothermal effect of CDots. The temperature rise leads to the phase transformation of TiO2 from the anatase TiO2 to the rutile TiO2. The phase transformation processes with volume changes result in the formation of the CDot and TiO2NP composite with sintered interior (with no obvious structures, Fig. 1b orange dashed rectangle) and microlens-shape surface (Fig. 1b, c). This is in sharp contrast to the surface morphology of the CDot and TiO2NP blend prior to the laser heating, which is made up of nanoparticles (Supplementary Fig. 3a–c). In addition, as can be seen from the transmission electron microscope (TEM) image shown in Fig. 1d, CDots in the interior of the CDot-TiO2 composite distribute homogeneously inside the TiO2 matrix. TiO2 and CDot in the composite exhibit the lattice spacings of 0.32 nm and 0.21 nm (Fig. 1e), which could be attributed to rutile TiO2 (110) (Fig. 1f) and graphitic carbon (100) (Fig. 1g), respectively. The CDot-TiO2 composite is further studied by X-ray-diffraction (XRD) (Fig. 1h), where the characteristic peaks at 21° and 27° are derived from the graphitic CDot and rutile TiO2, respectively, thus confirming the structure of CDot and TiO2 inside the composite. Note that TiO2 in the CDot and TiO2NP blend prior to the laser heating is anatase (Supplementary Fig. 4), indicating that TiO2 undergoes the anatase-to-rutile transition during the laser heating process. Furthermore, as shown in the Fourier transform infrared (FTIR) spectroscopy measurements (Supplementary Fig. 5), the CDot-TiO2 composite (Supplementary Fig. 5 orange curve) exhibits the characteristic peaks from both TiO2 (the broad peak in the range of 500–700 cm−1 originating from the stretching vibration of Ti–O and Ti–O–Ti bonds32, Supplementary Fig. 5 green curve) and CDot (the peak at 1250 cm−1 which originates from the stretching vibrations of the surface C–O, Supplementary Fig. 5 black curve)33. The appearance of a new peak at 952 cm−1 is observed which may be ascribed to the formation of C–O–Ti bonds between CDot and TiO2. The CDot and TiO2 interface is further evaluated by characterizing the sectioned CDot-TiO2 composite using X-ray photoelectron spectroscopy (XPS). As can be seen from Supplementary Fig. 6, in addition to the peaks of Ti-O (529.7 eV, Supplementary Fig. 6d), C–C/C=C (284.4 eV), C–O (286.2 eV) (Supplementary Fig. 6c), C=O (531.3 eV) and –OH (533.1 eV) (Supplementary Fig. 6d), the appearance of the peaks at around 282.1 eV and 288.8 V are originated from the Ti–C and C–O–Ti bonds (Supplementary Fig. 6c) formed at the CDot and TiO2 interface34. Moreover, the CDot-TiO2 composite (Supplementary Fig. 7a) shows a broad absorption peak in the UV region which is likely due to the band gap absorption of TiO2NP (Supplementary Fig. 7b) and the π–π* transition of the conjugated π-domains of CDot (Supplementary Fig. 7c). The significantly increased absorbance of the CDot-TiO2 composite in the NIR region (Supplementary Fig. 7a) as compared to that of the CDot and TiO2NP blend prior to the laser heating (Supplementary Fig. 7d) may be ascribed to the newly formed carbon and TiO2 interface. This thus lays the foundation for the CDot-TiO2 composite to absorb the NIR light and undergo the light conversion.
Highly directional white-light emission
The CDot-TiO2 composite emits the directional white light in air once it is excited by the NIR light (Fig. 2a, b), featuring a solid angle as narrow as 1/60 (Fig. 2c, Supplementary Fig. 8 and the descriptions therein). As can be seen from the emission spectrum shown in Fig. 2d, the emission from the CDot-TiO2 composite covers both the visible and NIR regions. The color temperature of the emitted white light resembles that of the black-body emission at ~3000 K (Supplementary Fig. 9a, b). In addition, as shown in Fig. 2e and Supplementary Fig. 10, the directional white light could be repetitively switched on (Fig. 2e red curve) by intermittently applying the NIR light excitation (10 s on then off) for 50 on and off cycles (Fig. 2e black curve). The CDot-TiO2 composite based white-light emitter also exhibits excellent air stability as evidenced by the stable emission with negligible changes in the emission intensity under NIR excitation (intermittent excitation over a time span of 100 days, as shown in Fig. 2f), which is likely due to the fact that TiO2 that encapsulates CDot helps improve the overall stability. In addition, as shown in Table S1, the light conversion efficiency is estimated to be ~11.8 %.
Fig. 2: Highly directional white-light emission.
a Side and b front views of the emitted white light from the CDot-TiO2 composite under the NIR light excitation in air. c The solid angle of the light emitted from the CDot-TiO2 composite when excited by the NIR light (only the emission with an intensity higher than 0.5 W/cm2 is shown). d The spectrum of the emitted white light. The white-light emission from the CDot-TiO2 composite (e) when applying the excitation NIR light repetitively (10 s on then off) or f intermittently every 10 days within 100 days. The red and black lines/dots in (e, f) denote the intensities of the emitted white light and the excitation NIR light, respectively. The insets in (e, f) are the images showing the emitted white light in different periods of time.
The mechanism of the highly directional white-light emission
We have studied the mechanism of the directional white-light emission by identifying the emission center, revealing the light emission mechanism and the origination of the directionality.
In order to identify the emission center, we have performed a series of control experiments. As shown in Supplementary Figs. 11–14, no emission is observed in case of the pristine or laser-heated TiO2NPs when excited by NIR light in air or in vacuum. In contrast, NIR driven white-light emission from the pristine CDots in vacuum is observed (Supplementary Fig. 15) which is omnidirectional. This white light exhibits the similar emission spectrum shape and color temperature as those of the CDot-TiO2 composite (Supplementary Fig. 15c and Fig. 16), indicating CDot is likely the emission center. Note that the emission from the pristine CDots in air only lasts for less than 1 s (Supplementary Fig. 17), which is possibly because of the poor air stability of the pristine CDots at the elevated temperature (Supplementary Fig. 18). On the contrary, the CDot-TiO2 composite could withstand a temperature as high as 800 °C (as determined by thermogravimetric analysis (TGA) in air, Fig. 3a), which is likely because TiO2 functions as an air isolating material (isolate CDots from air), thus laying the foundation of its stable white-light emission in air.
Fig. 3: The mechanism of the highly directional white-light emission.
a Thermogravimetric analysis (TGA) curve of the CDot-TiO2 composite (in air). b Experimental (solid green curve) and simulated (dotted red curve) spectra of the emitted white light. c The fluorescence intensity of Y2Mo4O15:Er3+/0.8Yb3+ encapsulated inside the CDot-TiO2 composite at 525 nm and 545 nm. Evolution of d temperature and e white-light emission intensity (at 700 nm) during the excitation and de-excitation transients. f The spectra of the emitted white light during the de-excitation process. 0 ms indicates the time when the excitation NIR light is removed. g Simulation model and the simulated directional light after a monochromatic 580 nm light passing through the microlens-shape surface in (h) the near (side view) and (i) far (top view) fields.
The spectrum of the white-light emission (Fig. 3b solid green curve) is composed of a broad peak and four characteristic peaks, at 1.22, 1.38, 1.65 and 1.84 eV, respectively. On one hand, the cyclic voltammetry (CV) curve of CDots illustrated in Supplementary Fig. 19 suggests an energy gap (Eg) of 2.25 eV35. Due to the low photon energy of the excitation NIR light (1.17 eV (1064 nm light)) which is lower than Eg of CDot, single photon could not excite the electrons in the ground state, instead it could accelerate them. CDot has a core consisting of multiple stacked layers of graphene-like sheets. It has been reported that the electron in graphene may exhibit a velocity which is 1/300 of the light speed. Under the NIR light (1.17 eV) irradiation, the electron may be accelerated to a speed further close to the light speed. And the deceleration of the electron may lead to the energy relaxation in the form of radiation, a process similar to bremsstrahlung. This mechanism could be simulated based on an anharmonic oscillator (detailed in Supplementary Note 1)28. As shown in Fig. 3b dotted red curve, the simulation result correlates well with the white-light emission spectrum (Fig. 3b solid green curve), confirming this emission mechanism. We have also studied the simulated curve in the long wavelength region. As shown in Supplementary Fig. 20, the simulation suggests that the broad emission peak may cover a wide range of near infrared region as well as a small part of the ultraviolet region. In addition, the blue shift of the spectrum onset under higher intensity excitation light (Supplementary Fig. 21) is also similar to the bremsstrahlung mechanism.
On the other hand, the electrons may be excited to the excitation state via a multiphoton absorption process. This is evidenced by the nonlinear relationship between the excitation light power and the emission white-light intensity (Supplementary Fig. 22). The number of photons involved in this process could be estimated to be approximately 4.69 based on the following equation: Iw∝PN, Where Iw is the white-light emission intensity, P is the power of the excitation light, and N is the number of photons involved in the process. The total energy Etotal of the absorbed photons could also be calculated according to the de Broglie relation25: Etotal = N?ωexc, where Etotal is the total energy, ? is Planck’s constant, and ωexc is the angular frequency of the excitation light. The total energy of 4.69 absorbed photons with photon energy of 1.17 eV (1064 nm light) is 5.49 eV, which is significantly higher than Eg of CDot (2.25 eV), indicating the feasibility of multiphoton excitation. In the CDot-TiO2 composite, because of the existence of defects and functional groups at the CDot and TiO2 interface36, multiple defect energies exist between the ground and excitation energies, which account for the appearance of the multiple characteristic peaks (at 1.22, 1.38, 1.65 and 1.84 eV). Note that, the white-light emission spectrum of the CDot-TiO2 composites exhibits a blue shift as compared to that of the pristine CDots (Supplementary Fig. 15c). This is possibly due to the higher energy level of TiO2 (3.2 eV of TiO2 vs 2.25 eV of CDots)37, which also demonstrates the involvement of the multiphoton excitation and emission processes. It is worth pointing out that Supplementary Fig. 22 also indicates that there may be other linear excitation mechanisms, such as surface plasmon resonance, photon-assisted tunneling and energy band transition, which are likely due to the carbon surface/interface states. Furthermore, we find that UV (365 nm, CaneLa SEO X9) or green (532 nm, Polars II) excitation light is unable to excite the CDot-TiO2 composite possibly due to the limitation in the low intensity of the light sources we have used. The non-linear processes could not be invoked unless the excitation light intensity exceeds a critical value.
In addition, it is worth pointing out that the white-light emission in the current study is not the black-body radiation. The temperature of the CDot-TiO2 composite under NIR light excitation is ~570 °C, which is estimated based on the ratio of the fluorescence intensities of Y2Mo4O15:Er3+/0.8Yb3+ encapsulated inside the CDot-TiO2 composite at 525 and 545 nm (Fig. 3c) via the Boltzmann relation38. This temperature is significantly lower than that of the black-body radiation (3000 K) with a similar emission spectrum. In addition, the characteristic peaks in the white-light emission spectrum of the CDot-TiO2 composite also differ significantly from that of the black-body radiation, which has only one broad spectral peak.
Furthermore, we have examined the evolution of temperature, emitted white-light intensity (at 700 nm) and spectrum shape as a function of time during the excitation and de-excitation processes. As shown in Figs. 3d, e, the time scales for both the temperature and emitted light intensity to reach the maximum are comparable (7.9 s vs 10 s) during the excitation process. However, during the de-excitation process, the emitted light intensity exhibits a much faster decay time (0.7 s) as compared to that of the temperature (4.5 s). The decay rate (τ) is measured to be 0.056 s in case of the emitted light intensity as opposed to 0.1763 s in the case of the temperature. When the excitation NIR light is turned off, the characteristic peaks in the emission spectrum which are derived from the multiphoton process disappear first and only the broad absorption peak caused by bremsstrahlung remains (Fig. 3f and the normalized curves shown in Supplementary Fig. 23). In addition, since the emitter operates at a temperature of ~570 °C, the temperature may also play a role. Based on the above results, we have tentatively proposed that the white light emission involves a process similar to bremsstrahlung, multiphoton and thermal processes.
The white-light emission from the CDot-TiO2 composite can be excited by a NIR light as weak as 0.5 W/cm2 in air and the white-light emission intensity increases with the increase of the excitation NIR light intensity (Supplementary Fig. 22). However, when the NIR excitation light intensity exceeds 10 W/cm2, the white-light intensity decreases, which is likely because the CDot-TiO2 composite is damaged by the high-intensity NIR light, the thermal quenching activated when a certain energy barrier is exceeded or the optical quenching (involving further excited state absorption, cross relaxation etc.) when photon flux is higher than a certain level. In addition, the white-light emission from the CDot-TiO2 composite is highly dependent on the CDot concentration inside the composite. As can be seen from Supplementary Fig. 24, there is no white-light emission when the CDot concentration is lower than 12 wt% and the emission intensity increases steadily with the increasing CDot concentration. However, the white-light intensity decreases when the CDot concentration is higher than 16 wt% and the emission disappears when the CDot concentration is higher than 20 wt%. This is likely because CDots lack air stability (Supplementary Fig. 18) during the white-light emission process so that the emission property deteriorates when too many CDots are present inside the composite. It is worth noting that other kinds of CDots, i.e. graphene CDots, nitrogen doped CDots and chiral CDots, could also emit directional white light.
The directionality of the emitted white light from the CDot-TiO2 composite is possibly because of the microlens-shape surface. Firstly, in order to rule out the directionality originates from the excitation light, we have performed more control experiments. As shown in Supplementary Fig. 25, when changing the angle of the excitation light, the directionality of the emitted white light shows negligible changes, which indicates that the directionality of the white light does not come from the excitation light source. Secondly, we have utilized the Finite Difference Time Domain (FDTD) method (detailed in Supplementary Note 2) to investigate the effect of the microlens-shaped surface on the white light emitted by CDots. A model structure that resembles the surface of the CDot-TiO2 composite is established (Fig. 3g). In the presence of the microlens-shape surface, the emitted white light generated by CDot could be confined and regulated by the surface structures in the near field (Fig. 3h), leading to the highly directional white-light emission in the far field (Fig. 3i). Note that the microlens-shape surface exhibits the confinement effect for light with different wavelengths in both near and far fields (Supplementary Fig. 26), thus accounting for the highly directional broadband white-light emission observed in the current study. This is also in contrast to the omnidirectional light emitted by the pristine CDots in vacuum, which are powders and have no surface structures (Supplementary Fig. 15). Note that, in an ideal system, etendue remains constant. However, in the current system, due to the light loss, the etendue increases.
Based on the above discussions, we tentatively attribute the directional white-light emission to the following mechanism (Fig. 4a–c): CDot functions as the emission center, which emits light based on a tentative mechanism that may combine a process similar bremsstrahlung, multiphoton and thermal processes. TiO2 could additionally act as the protective matrix to help stabilize CDots in air. The white light emitted from CDots could be regulated and confined by the microlens-shape surface, resulting in the high directionality (Fig. 4d).
Fig. 4: Schematic illustration of the mechanism of the directional white-light emission and the potential application demonstration of the white-light emitter.
a Schematic depicting the mechanism of the highly directional white-light emission involving b the intraband process based on a process similar to bremsstrahlung, c the interband transition based on the multiphoton process and d near-field confinement and regulation of the emitted white light enabled by the microlens-shape surface. e Schematic showing the potential application demonstration of the directional white-light emitter based on the CDot-TiO2 composite as the light source of a projector. The corresponding side and front view charge-coupled device (CCD) images are shown in (f) and (g), respectively.
Potential application demonstration of the highly directional white-light emitter
The directional white-light emitter may have great potentials in targeted illumination and projection. As a proof-of-the-concept, we have demonstrated its potential as the headlight of a model car (Supplementary Fig. 27a). To this end, the CDot-TiO2 composite is first sandwiched between two quartz slides (Supplementary Fig. 27b), which is then mounted in the front of a model car (Supplementary Fig. 27c, d). As can be seen from Supplementary Fig. 27e, the white light emitted from the CDot-TiO2 composite is angled toward the road. And due to the directional feature of the white-light emitter (1/60 solid angle), only a circular cone ahead of the model car is illuminated. This is of particular interest because the reduced illumination cone could effectively minimize the glare which is attractive for applications such as vehicle headlights. The highly directional white-light emitter also has potential applications in a projection system. As shown in Fig. 4e–g, the projector based on this white-light emitter could directly project the image on a polyethylene terephthalate slide (a bird) to the screen without the utilization of optical elements.
Discussion
The highly directional white-light emission from the CDot-based emitter excited by monochromatic NIR light is realized without the utilization of optical elements by harnessing the synergistic interactions between the two constituents inside the emitter, i.e., CDot and TiO2. Among others, CDot functions as the center of white-light emission based on a tentative mechanism involving a process similar to bremsstrahlung, multiphoton and thermal processes, while TiO2 acts as a stabilizer. In addition, the microlens-shape surface of the emitter regulates the emitted white light into a directional one with 1/60 solid angle. The CDot-based directional emitter exhibits excellent working stability and repeatability in air. Given the low cost and easily obtainable feature of both CDot and TiO2, together with the reduced size and energy requirements due to the absence of optical elements, we anticipate that the directional white light could have great potentials in a wide range of applications. Among others, its applications in the fields of target illumination and projection are straightforward.
Methods
Materials
The CDot (3–10 nm) solution was synthesized by a typical electrochemical method39. The TiO2NP (10 nm) solution was obtained from Xuan Cheng Jing Rui New Material Co., Ltd. Y2Mo4O15:Er3+/0.8Yb3+ was synthesized according to the literature method38. Tetrabutylammonium hexafluorophosphate, ferrocene and acetone were purchased from Sigma-Aldrich Company. The toy car was purchased from the XST Company, China.
Fabrication methods
The solution containing CDot and TiO2NP with different weight ratio was mixed first, which was then precipitated through centrifugation at 10619 × g for 10 min. The resulting paste consisting of both CDot and TiO2NP was then coated on a quartz slide and allowed to dry in air. The dried CDot and TiO2NP blend was then subject to the laser heating (10 W/cm2 1064 nm laser, Changchun Laser Optoelectronics Technology Co., FC-1064-10W) for 2 s, which resulted in the formation of the CDot-TiO2 composite. The CDot-TiO2 composite containing Y2Mo4O15:Er3+/0.8Yb3+ was synthesized in a similar way except 10 wt% Y2Mo4O15:Er3+/0.8Yb3+ was added to the mixture solution of CDot and TiO2NP.
Characterizations
SEM images were obtained by a Zeiss Supra55 scanning electron microscope. TEM and HRTEM images were collected using a FEI-Titan G280-200 Chemi scanning transmission electron microscope with an accelerating voltage of 200 kV. XRD was carried out on the PIXcel3D X-ray diffractometer (Empyrean, Holland Panalytical) with Cu Kα radiation (λ = 0.154 nm). The FTIR spectra were measured on a Hyperion spectrophotometer (Bruker) using a standard KBr pellet. UV–vis-NIR spectrophotometer (Lambda 750, PerkinElmer) was employed to acquire the UV-vis-NIR absorption spectra. XPS measurements were conducted on a KRATOS Axis ultra-DLD X-ray photo-electron spectroscope with a monochromatic Al Kα X-ray source. A NIR laser is utilized (FC-1064-10W), which has a wavelength of 1064 nm and a beam spot of 5 mm. The laser was placed 1.7 cm away from the CDot-TiO2 composite and applied from the vertical direction. A detector (AvaSpec-ULS2048CL-EV0) was used to measure the emitted light. The detector was placed 5 cm away from the CDot-TiO2 composite. The collection angle was 90° with respect to the direction of the excitation laser. Unless otherwise mentioned, the CDot concentration inside the CDot-TiO2 composite, the NIR light intensity used to excite the CDot-TiO2 composite were fixed at 16 wt% and 9 W/cm2, respectively. The CDot concentration inside the CDot-TiO2 composite was estimated based on the CDot concentration in the CDot and TiO2NP blend prior to the laser heating. The emission from the pristine CDots under NIR light excitation in vacuum was obtained in a similar fashion except that CDots were sealed in a vacuum quartz tube. The intensity of the white-light emission from the CDot-TiO2 composite was measured by the optical power meter (LM-10 HTD, Coherent Inc.). TGA was conducted in air from ~30 °C to 800 °C at a heating rate of 5 °C/min on a METTLER TOLEDO TGA1 analysis system. CCD Images were captured by the SONY DSC-RX10III digital camera. The simulation was conducted based on the Ansys Lumerical 2020 r2 finite software.
Journal
Jul. 13, 2025
