Understanding continuous wave laser-induced chemical reactions at micro- and nano-diamond-glass interface under infrared excitation

This work addresses the issue of laser-induced white light generation by nano- and micro-diamond powder and the accompanying redox processes occurring at the surface of the particles. The broadband white light is generated by near infra-red continuous wave laser (975 nm) on micro and nano-diamond powders sealed in lightbulb-like devices. It is shown that the emission from diamond samples is a highly nonlinear process with apparent saturation close to 1 W of the optical excitation power. Multiband mechanism and mixed hybridization at particle surface are further discussed as a possible origin of the white light emission. Changes in the sp2/sp3 ratio upon the laser excitation are here discussed in terms of molecular dynamics simulations. Observed surface changes related to diamond graphitization are considered further as possible pathways for chemical reactions at the interface of the glass and diamond samples. Obtained results bring relevant physical premises according to the possible mechanism responsible for the white emission from diamond-like carbon materials, its mechanisms, and an essential figure of merit considering the diverse applicability of this phenomenon in various electronic devices.


Introduction
Observation of laser-induced white light emissions (LIWE) from oxide materials by Tanner's and Wang's in 2010 caused an extensive increase in scientific interest in this field and the potential applicability of the phenomenon materials, including lanthanide oxides [1, 2], semiconductors [3], metals [4], and at least two different allotropic forms of carbon, i.e., diamonds [5,6], graphene and graphene-based composites [7,8].There are several features of the phenomenon that are worth to be noted.Firstly, LIWE is a nonlinear process characterized by a clear threshold point usually dependent on the excitation photon energy.This indicates the universal nature of the phenomenon itself, which is more closely related to interface processes than the composition-dependent properties of a material.
Despite extensive research in recent years, there is still no comprehensive description of the process caused by the complexity and multiplicity or mechanisms involved in its build-up.Regarding the temporal characteristics, the rise time for LIWE is moderately slow, ranging at 1 s and, after ignition, stable under fixed conditions.However, these parameters may vary quantitatively between different materials; the process is immutable.Further, LIWE is observed only for samples placed in a vacuum, which decays rapidly with increasing pressure.
Recent studies strongly indicate that LIWE is a surface-related phenomenon.Even if the excitation beam can penetrate the sample and excite color-center emission from its interior, white light emission occurs only on the surface towards the exterior [9].It has already been shown that LIWE is associated with an electron emission from the sample's surface on the matter-vacuum interface [10].Such emission is commonly associated with a photon-enhanced thermionic emission mechanism [10,11].Recent results show that photoionized electrons form a space charge region on the surface of the sample.Depletion of electrons on the surface of the materials may further be responsible for bond breaking and hybridization change leading to photoinduced phase transitions [6].
Interestingly, several studies have also reported an increase in LIWE intensity with increasing pressure [5,12,13]; thus, the vacuum necessity for the emission must be a case-specific situation.Moreover, recent experiments performed on LIWE generation on graphene foam immersed in alcohol revealed very efficient hydrogen generation [14,15].This indicates that chemical reactions may occur at the interface sample/medium during LIWE generation catalyzed by a high photoionized electron cloud density.Diamond, as a highly crystalline carbon material with mixed hybridization on the surface, has demonstrated interesting properties regarding photoinduced structural changes [6,16,17].This work investigates the effects on sample/medium interface during LIWE generation on samples enclosed in glass.Diamond powders of two sizes were then chosen as representative samples for LIWE generation in both vacuum and glass matrices.The possible existence of mixed hybridization at the material's surface is considered critical for efficient electron ionization.One may expect that the space charge-induced reactions on the sample/glass interface may influence the stability of LIWE and hence the performance of future devices.

Materials
The nanosized diamond powder used in the study was obtained commercially and synthesized through a detonation method, which is similar to the method described by K Iakoubovskii et al [18].It is important to note that nanosized diamonds synthesized through this method typically have various functional groups present on the surface of the grains [19,20].More information on this specific synthesis method can be found in the supplementary information of the research paper and in publications by [21,22].The micro-diamonds used in the study were also obtained from an external source.The synthesis of these micro-diamonds was performed using a high-pressure, high-temperature (HPHT) sintering method [23,24].Additional details regarding the synthesis process can be found in the supplementary information of the paper.The characterization of the samples is described in more detail in previous work [25].

Device preparation
The two diamond samples were placed under a vacuum in glass bowls and then sealed.The glass matrix covered the samples from the outside, forming a kind of optical fiber filled with diamond particles.Next, the quartz glass (SiO 2 ) was heated up to the point of melting glass (1600 °C) and pulled downwards t.o create thin capillaries, to which the diamonds were then engrafted inside to form a light bulb-like device.The μD capillaries are visually maximum of 3 mm in diameter, with micro-diamonds located loosely inside the SiO 2 .The nD capillaries, on the other hand, have a form of a thin film covered in a glass matrix, and they are slightly wider.The film mentioned above has changed color due to touching the melted silica.In order to evaluate the level of surface phase transition-both samples were then cut in half and wiped clean.Then the material was poured out easily to extract the material from the sample mechanically.

Spectroscopic measurements
The LIWE spectra taken from the glass-sealed diamond powder were compared to the results from pure diamond powder kept in the vacuum chamber.The EXT75DX Turbo Molecular High Vacuum Pump with a connected TIC controller (Edwards) was used to perform the measurements at low-pressure conditions (ca. 10 −4 MPa).The power dependence was measured with an AVS-USB2000 Spectrometer (Avantes).The 2 W of optical power, 975 nm CW (continuous wave) diode laser with a lasing threshold at 400 mA was used as the excitation source.The size of the spot was measured on the sensor to be 0.017 mm 2 .Half of the total laser optical power is contained in this focal spot, which is 1.5 W. Derived from that, the power density of the focused laser beam was determined to be 8.7•10 6 W m −2 at maximum, accordingly to the FWHM definition of the focal spot.More details on the experimental setup and video recording of one of the trials may be found in the supplementary information.

XRD measurements
Powder x-ray diffraction patterns were gathered using an X'Pert PRO x-ray diffraction system that was equipped with a PIXcel ultrafast line detector.The measurements were performed in the reflection mode, utilizing CuKα radiation; the x-ray tube settings were 40 kV and 30 mA.

Electron microscopy
The structure and morphology of diamond samples were examined before and after embedding them into the capillaries.Both samples were characterized by Scanning Electron Microscopy (SEM) using the Helios G4 PFIB CXe DualBeam FIB/SEM microscope.The nDs were also analyzed using Transmission Electron Microscopy (TEM) using a Philips CM-20 SuperTwin TEM microscope operating at 160 kV.

MD simulations
Molecular dynamics calculations were performed in LAMMPS [26] package using bond-order AIREBO potential [27].The simulated system consisted of 1916 carbon atoms in periodic boundary conditions on the XY plane.Simulations were conducted in the NVE ensemble at 0 K.The coordination number of carbon atoms was investigated using the algorithm checking the distances between the center points of the atoms.The cut-off that the C-C bond can extend is fixed at 1.65 Å because the minimum bond length in a diamond is 1.54 Å, and the maximum diamond bond length for the AIREBO force field is 1.7 Å.The details on how this algorithm works can be found in LAMMPS manual.

Results and discussion
Diamond powders were selected for a study on photoinduced phenomena at the interface between the sample and the glass matrix.Notably, micro-diamonds (μDs) and nano-diamonds (nDs) appear visually distinct due to the latter's higher specific surface area [20,28,29].Micro-diamonds can be distinguished from each other, some of which are transparent with a faint green hue caused by nitrogen substitutions during synthesis [30].In contrast, nDs undergo a structural phase transition during the enclosing process in glass capillaries, resulting in a blackened surface.This transition occurs at a temperature close to the thermal graphitization of diamonds, approximately 1600 °C.After exposure to molten glass, the collected samples were analyzed to assess the extent of the aforementioned process through a detailed examination of the ordered structures.

XRD
To characterize the structure of the samples, x-ray diffraction (XRD) analysis was conducted.The reference pattern (figure 1(a)), along with the experimental data (COD 9008564), was included.Figures 1(b) and (c) show the diffraction patterns of μDs before and after embedding in silica glass, respectively.The most prominent diamond reflection, associated with (111) planes, was located at 43°for 2θ, while the other at 75°was associated with (220) diamond planes.Minor peaks observed at 30°to 40°were attributed to nitrogen [23,31] and metals remaining in the structure were residues of the catalysts used in the synthesis [32,33].Figures 1(d) and (e) display representative x-ray diffraction (XRD) outcomes obtained for nDs.The amorphic phase gives rise to a broad peak ranging from 10°to 25°.Additionally, the nD samples exhibit slight graphitic reflections at 26°attributed to (002) planes.The XRD pattern of the nDs that were enclosed in glass (figure 1(e)) is akin to that of the sample before the encapsulation process (figure 1(d)).However, slight alterations in the reflection from (111) planes imply that the nDs experienced thermally induced amorphization to some extent.
The size of the grains calculated from the Scherrer equation [34], with the shape factor for the carbon materials based on the work of Biscoe and Warren [35] was 7.8 nm averaged for the nano-diamonds.

SEM analysis
In figure 2, scanning electron microscope (SEM) images were utilized to determine the average size of μD grains, which measured between 100-200 micrometers in diameter.Grain boundaries were visible in the samples, as well as slight ledges and terraces on the surface of each grain, yet overall the grains appeared to be wellcrystallized.No discernible alterations were visible on the surface presented in figure 2(d) compared to figure 2(c), which represents the sample before heating.The SEM image of the nDs (figure 2(b)) depicted a surface that was highly elevated.However, no distinguishable grains were evident, necessitating further investigation of the sample.

TEM analysis
High-resolution transmission electron microscope (HRTEM) images were taken of the nDs both before (figures 3(a)-(c)) and after (figures 3(d)-(f)) their introduction to molten glass.The captured images revealed that the size of the grains rarely exceeded 10 nm.The nDs particles were found to be agglomerated, forming chain-like structures similar to those described by Stehlik and Baitinger [36][37][38].Analysis of interplanar distances (figure 3(e)) confirmed the nDs diamond structure, as evidenced by a d-spacing of 0.2 nm corresponding to the (111) planes of the diamond lattice.Electron beam diffraction from the selected area also showed clear reflections from (111), (220), and (311) planes, further confirming the presence of sp 3 hybridization in the core of the grains.

Spectroscopic measurements
The power dependencies in figure 4 were derived from subsequent excitation of the samples with 975 nm of continuous wave (CW) laser diode, and has been presented without radiometrical calibration.Both samples manifested broadband LIWE spectra centered at about 670 nm.The observed intensity of the LIWE increased exponentially with the excitation power.Additionally, Raman spectra presented in the supplementary information were measured to assess structural changes of the samples in a vacuum.Micro-diamonds embedded in capillaries manifested strong emission with a pulse-like behavior.The emission experiments were repeatable, and throughout the whole irradiation period, the capillary emitted bright pulsating light, which often faded quickly to almost complete absence.However, several times during the experiment, the emission started spontaneously again, only to disappear after a few seconds.A video of such an event can be found in the supplementary information.Additionally, after some time of the nDs sample irradiation, visible marks of the laser beam were present on the sample, without the diamond powder inside the capillary.
A commonly accepted description of stimulated white light emission spectra from luminescent materials in the convention of the strong electromagnetic field photoionization is a theory proposed by Keldysh [8].However, it is essential to notice that the formalism mentioned above is correct for the strong-intensity regime, where a static electromagnetic field enables the electron tunneling effects.The value of N is the order parameter of the process, as shown in figure 4. It is well scalable with the multiphoton absorption rate and may be described by the µ I P , N where P is the power of the incident laser.Parameter N from the preceding formula is usually considered the indicator of the number of photons absorbed in this process.However, as shown in previous works, in the LIWE generation from carbon materials, it may instead be interpreted as the corresponding electronic density accumulation in the avalanche ionization process [8,39].A LIWE threshold at 0.25 and 0.3 W for nDs and μDs, respectively, uphold this approach since it cannot be directly associated with multiphoton absorption.

Surface phase transition
The chemical activity of the space charge accumulated at the interface diamond/glass through the LIWE mechanism may be well examined experimentally by looking at the glass-sealed diamond powders (figure 5).One may note the formation of gas bubbles inside the capillary wall after LIWE generation (figure 5(b)).Another significant result of CW IR treatment is visible discoloration of the diamond grains.Usually, this is caused by the sample graphitization, which, together with the heat applied through IR irradiation and the gas bubbles on the surface of the grains, can indicate the reaction of carbon oxidation in the presence of silica dioxide [40].Interestingly, the LIWE generation from the nDs capillaries created visible brighter marks with a lack of carbon material (figure 5(d)) compared to the samples before irradiation (figure 5(c)).The degradation can influence the absence of particles in irradiation spots because of the mentioned above reaction with the matrix.Another explanation for the material not being present in the irradiated spots is the electrostatic repulsion of the grains, as  the diamond particles are considered novel semiconducting material for manufacturing laser-driven FETs [41,42].
After generating LIWE, blackening the diamond grains becomes an important physical factor in relation to the surface graphitization of the diamond.Our previous work [6] has already shown similar outcomes.The blackening of the diamond grains can be undoubtedly attributed to a change in hybridization, i.e., sp 3 to sp 2 , caused by the intense IR irradiation and ionization of electronic charge located in the surface states.It is worth noting that ionization of electrons localized at surface is much more likely than interbond excitation of valence band electrons, as non-bonding electrons and electrons involved in surface charge minimization due to the interface's presence are energetically unfavorable.Once ionized by intense IR laser irradiation, surface carbon atoms undergo structural relaxation.It is reasonable to assume that the returning electron will have different conditions than those present before the laser irradiation, and it will be less probable for such an electron to return to the diamond's structure.As a result, a more favorable phase with a predominance of sp 2 hybridization will be formed.Such reasoning seems to support the claim that the blackening is attributed to surface graphitization.

Decay time
To further investigate the interaction with the environment, the integral intensity of the emission was measured over time and compared to samples without a glass coating.Figures 6(a) and (b) illustrate the decay time for the diamonds alone in a vacuum and the glass-coated diamond capillaries, respectively.The emission intensity shows a noticeable decay over time, particularly within 2 s, for the capillaries.In contrast, compared to the samples in a vacuum, the emission remains relatively stable, with a slight increase at the beginning of the irradiation.However, in the case of the capillaries, despite their stability, the emission is associated with the degradation of the samples, leading to a more pronounced decay in the emission.This highlights the importance of a vacuum environment for fabricating durable devices.

MD simulation
To further investigate the interaction with the environment, the integral intensity of the emission was measured over time and compared to samples without a glass coating.Figures 6(a) and (b) illustrate the decay time for the diamonds alone in a vacuum and the glass-coated diamond capillaries, respectively.The emission intensity shows a noticeable decay over time, particularly within 2 s, for the capillaries.In contrast, compared to the samples in a vacuum, the emission remains relatively stable, with a slight increase at the beginning of the irradiation.However, in the case of the capillaries, despite their stability, the emission is associated with the degradation of the samples, leading to a more pronounced decay in the emission.This highlights the importance of a vacuum environment for fabricating durable devices.
In a similar manner, the latter can be divided into three regimes, which are indicated by colored lines in figure 7. The violet line represents the energy level below the threshold for the hybridization switch.Similar to the case shown in figure 4, there is an energy level from which the number of broken bonds starts to increase rapidly, depicted by the red line.Above this range, the green line indicates the energy levels at which the diamond surface reaches full saturation of this process.As demonstrated earlier, the number of excited states grows exponentially with the incident laser power.However, the number of excited states also acts as a limiting factor, causing the process to eventually stop.In the LAMMPS package, the kinetic energy is derived from the system's temperature, which stands in line with the thermionic processes as the driving force of the ionization.Formula describing avalance ionization process, mentioned during the interpretation of power dependence spectra (figure 4) can be correlated to the catalytic activation energy.For the surfaces of monocrtstaline solids it can be wrote in a conventional Arrhenius term [44][45][46], and in this sense the emission intensity it may be correlated as such: where T -is the system temperature, k B -is Boltzmann constant and E A accounts for the activation energy- the energy added to the system in the simulation to replicate the graphitization process.The plot's shape bears resemblance to the power dependence of LIWE, implying a potential correlation between emission and hybridization change on the surface of the diamond grains.The amount of energy introduced to the surface in the simulation is increased to simulate the change in power of the incident laser in an experimental setting.In theory, this statistical description of photo-controllable sp 2 /sp 3 switching could be extended to larger diamond systems, allowing for the prediction of technical conditions required for laser-driven fabrication of carbon materials with mixed hybridization [11,[47][48][49].However, to fully understand the energetic limits of the process, it would be necessary to adjust the system size, as the results obtained from a system of slightly less than 2000 atoms can only theoretically correspond to the energy changes within the simulated system.

LIWE mechanism
Previous studies have made several attempts to elucidate the mechanism behind Laser-Induced White Emission (LIWE).In one particular study [11], the authors discussed technological advancements possible to achieve by transforming single crystal diamond into a composite material with mixed hybridization through graphitization.The authors main focus is on the femtosecond (fs) laser fabrication of electrodes for innovative photon-enhanced thermionic emission solar cells, however various experimental reports have been published on laser-driven graphitization [16,[50][51][52].
Indeed, the thermalization of electrons plays a significant role in the graphitization process.Previous studies on LIWE generation from carbon materials have provided evidence of infrared continuous wave (CW) excitation incandescence [6-8, 14, 53-55].Therefore, the influence of temperature cannot be overlooked when considering the mechanisms responsible for the various interconnected effects during LIWE.Mechanical stress exerted on the surface, which leads to surface relaxation, is closely linked to non-radiative electron-hole recombination processes.During such processes, the energy of electrons is converted into phonons.This effect is responsible for heating the sample at the surface and at the glass-diamond interface.The temperature recorded under 1.5 W of 975 nm excitation reached a maximum of 900 K for the graphene ceramics [7].Initially, the black body radiation theory was dismissed as the thermal white light emission occurred at much higher temperature levels.In the mentioned work, low temperature (10 K) emission measurements were also conducted, further confirming the complexity of the process beyond mere incandescence.However, it is important to acknowledge that an appropriate level of heat increase does result from the white light emission of carbon-based materials.Son et al [56] proposed the fabrication of single-layer graphene photoemitting devices within a photonic cavity regime, where emission occurs due to Joule heating.The temperature levels in such experiments ranged from 1500 to 2500 K, which aligns with the melted quartz glass observed in figure 6(b).
The graphitization process is commonly considered to be irreversible [11,49] due to the slightly lower potential energy of the graphite phase, which is only 0.02 eV/atom higher compared to diamond.However, it requires fifteen times more energy to surpass the threshold for the phase transition process [6,57].Nevertheless, previous studies have demonstrated structural transformations occurring when carbon atoms are excited by femtosecond lasers, even resulting in the creation of sp 3 -bonds between two layers of highly oriented pyrolytic graphite (HOPG) [53,55,58].In one experiment, a new stable phase of carbon called diaphite, with mixed sp 2 /sp 3 hybridization.This suggests the existence of a hidden metastable state between graphite and di [53,55,58].In one experiment, a new stable phase of carbon called diaphite, with mixed sp 2 /sp 3 hybridization.This suggests the existence of a hidden metastable state between graphite and diamond, where electronic excitation can cause an electron to transition from the π to π * band at approximately 2.2 eV [6], generating an electron-hole pair.This initial event leads to the generation of mechanical stress and the breakdown of symmetry.Consequently, more diaphite domains are formed, and the structure may ultimately create so many sp 3 bonds to be considered as diamond.This effect is analogous to the intervalence charge transfer (IVCT) mechanism proposed by Seijo et al [1,59] in lanthanide oxide compounds.
A similar effect to the intervalence charge transfer (IVCT) can be achieved through continuous wave (CW) excitation on the surface of initially defected diamonds.In this process, an electron is transferred from the valence band to the conduction band.The band gap of pure diamond crystal is approximately 5.5 eV, and the measured work function of diamond films is around 4.6 eV [60].In theory, for bulk diamond to become conductive under photoexcitation, it would require the absorption of around 3-5 photons with a wavelength of 975 nm, which is significantly higher than the observed experimental results.However, in the specific case being discussed, the emission likely occurs on the surface, where the atoms have different bonding structures [20,28,29].The surface region is rich in structural defects such as steps, vacancies, or ledges, which provide electron states with sp 2 hybridization, acting as trap states for carriers [61][62][63][64].
Surface electrons are more easily excited, making them responsible for the electron cloud on the surface.During this process, electron-phonon coupling leads to the relaxation of surface states and photoluminescence.When a sample is excited by a laser, the abundance of surface effects facilitates the movement of electrons from the valence to the conduction band.However, due to the lack of neighboring atoms in the crystal lattice, some valence electrons are unable to form bonds. Partially filled electron orbitals on the surface act as recombination centers.The N parameter values (shown in figure 4) for the integral intensity of the emission, which correlates with the photoionization energy, range from 2.16 for the nDs sample to 1.89 for the μDs sample.
The mechanism of ionization on the diamond surface is attributed to the aforementioned electron transfer from π to π * orbitals [6].This process is directly related to the number of surface defects and π states, as they play a crucial role in non-radiative recombination processes.The diamond structure, being covalent with a wide band gap, requires a significant amount of energy for purely electronic anti-Stokes emission.However, impurities from the metallic catalyst used in synthesis can act as active centers for exciting the diamond structure.Any surface anomaly or defect can serve as a trigger for avalanche ionization, effectively reducing the energy threshold required to generate free electrons [6,39].This threshold is even lower for diamonds without a glass coating since it is easier to maintain the vacuum conditions necessary for more efficient LIWE generation [65].Excited surface electrons, induced by CW energy, transition to a near-free state, forming an electron cloud and emitting visible photons.
Figure 8 illustrates the proposed mechanism of electronic diamond emission, which has been previously mentioned in other studies [6][7][8]57].In order for the conduction electron of bulk diamonds to overlap the forbidden band, it would need to absorb 5.5 eV of energy (figure 8(c)).However, the surface emission phenomenon is likely attributed to nonadiabatic electron transfer between potential wells with different hybridizations.This occurs due to the presence of surface trap states, represented as E ,

∆
on the diagram, which effectively lower the energy threshold E I (∆ )required for efficient emission.Multiphoton absorption can transition surface electrons from the ground state to an ionized near-free state, which then relaxes into a sp 2 -geometry initiating the avalanche graphitization of the entire grain.During this relaxation process, anti-Stokes emission of photons occurs.It should be noted that while a transition from sp 2 to sp 3 geometry is possible [55, 57, 66, 67], the reverse direction of this process is more favorable [11,49] due to the lower energy of the graphite structure.This statement is supported by experimental evidence, as the samples demonstrate some level of saturation after long periods of irradiation.
Nano-diamond (nDs) samples exhibit more rapid degradation compared to micro-diamond (μDs) samples.This can be attributed to the higher specific surface area of nDs, which lowers the threshold energy required for electron-hole recombination.Additionally, the synthesis route of nDs introduces functional groups on the surface of the particles, which can further affect the energy dynamics.Another factor contributing to the degradation is the excess energy from laser irradiation.The combination of heat and electrostatic repulsion can induce thermal movements in the sample, causing the material to move out of the focal plane of the laser diode.Similarly, this thermal displacement may be responsible for the pulsating emission observed in the μDs sample, as it pushes grains out of the focal plane.
The presence of bubbles on the surface of diamonds suggests carbon oxidation, likely resulting in the formation of CO 2 .As there was no oxygen present in the system during the encapsulation process, it is believed to have originated from the silica oxide on the ionized diamond surface.Nagamori et al [40,68] discussed various competing phases in the Si-C-O system thermodynamics.The oxidation reaction can be seen as the degradation of the sample, as the resulting products are no longer considered photoluminescent materials.
Mahoney et al [69] proposed similar mechanisms for the ionization of diamonds, which can be schematically represented as nD + N• n  → nD * + - e , occurring concurrently with the hybridization switch mentioned earlier [6].In this context, the primary chemical reaction taking place at the diamond-silica interface would involve the photocatalyzed single replacement process, resulting in the formation of carbon dioxide and metallic silicon.This type of reaction, albeit heat-activated, is commonly employed in the manufacturing of silicon using graphite or amorphous carbon as carbon sources [70].In this case, photoexcited diamonds can be regarded as an electron source, acting as a catalyst for the aforementioned reaction [71].Similar mechanisms can also be observed in the photocatalytic splitting of water or organic solvents using graphene-based materials [14,72].

Conclusions
This study aimed to investigate the generation of laser-induced white emission (LIWE) in carbon-based materials with a diamond structure and assess the feasibility of a glass-diamond light-emitting device.The analysis focused on micro-diamonds (μDs) and nano-diamonds (nDs), comparing their LIWE before and after encapsulation in glass capillaries.
The results revealed intense white light emission from both confined and unconfined diamond samples.However, the nDs exhibited rapid degeneration, making it challenging to measure their emission within the capillaries.Conversely, the μDs showed pulsating emission, which was highly intense when confined in the capillaries.The N parameter, indicating integral intensity of emission, was more easily measurable for samples without glass coating, suggesting better vacuum conditions.
During the experimental analysis, visible degradation marks caused by the laser beam and gas bubbles at the glass interface were observed.Molecular dynamics simulations were employed to investigate the hybridization change at the surface interlayer bond, revealing a correlation between the change in carbon atom hybridization and the emission intensity profile.This implies a relationship between the hybridization state of carbon atoms and LIWE occurrence.
However, material degradation inside the glass capillaries emerged as a significant hindrance in the manufacturing of glass-diamond devices.This degradation poses limitations to the long-term stability and functionality of such devices, necessitating further research and development efforts to optimize the manufacturing process and address these challenges.
The prototype of a glass-diamond light bulb or optic fiber requires revision due to material degradation and the negative impact of phase mixing on photoluminescence.However, the presence of a hybridization switch on the sample's surface and the potential for anti-Stokes emission offer technological possibilities.Exploring alternative matrix materials, such as monocrystalline hexagonal boron nitride (hBN), may overcome these limitations, enabling more stable emission without the need for a vacuum environment.
Although the specific application of a glass-diamond device may face challenges, diamonds can still be employed as laser-induced white light sources in other applications.For example, they can be utilized in LiFi devices for wireless communication or in optical memory storage based on nanosized carbon, taking advantage of the hybridization switch saturation.
Moreover, the presence of an electron cloud suggests that diamonds, like other carbon materials, possess efficient photocatalytic properties, opening doors to advancements in various technological applications.

Figure 1 .
Figure 1.The upper part depicts a reference pattern (a) for a diamond structure (COD 9008564).Below are x-ray diffraction patterns from the samples before (b, d) and after (c, e) the process of planting them inside the glass.The insets next to the diffractograms are a magnification of the 30°-40°and 70°-80°sections coloured accordingly.

Figure 2 .
Figure 2. SEM images of diamond samples.Images show the bulk of the μDs (a) and nDs (b) samples.nDs surface area development is much more apparent than μDs.The images below represent close-ups of the μD surface before (c) and after (d) introducing them to molten glass.

Figure 3 .
Figure 3. HRTEM images and electron diffraction patterns from nDs samples before (a b c) and after (d e f) exposing them to molten glass.Figures (c) and (f) are electron diffraction patterns from the diamond lattices.

Figure 4 .
Figure 4. 975 nm excitation power dependence and integral intensity with slopes marked of the LIWE from the μDs (a), (b) and nDs (c), (d) samples in vacuum, insets showing the emission.

Figure 5 .
Figure 5. Glass capillaries filled with micro-diamonds before (a) and after (b) laser excitation.The second picture shows gas bubbles and discoloration on the diamond surface.Close-ups are shown on the nDs capillaries before (c) and after (d) laser irradiation, marked by brighter spots where the carbon material is absent.

Figure 6 .
Figure 6.The decay time for the emission of nano (a) and micro (b) diamonds in a vacuum and in glass coating are presented, respectively.Samples confined in capillaries show rapid degeneration; slightly longer nDs capillaries emission time suggests this is a surface-related phenomenon.Insets showing the emission accordingly.

Figure 7 .
Figure 7. Molecular dynamics simulation graph showing the percentage of sp 3 /sp 2 carbon atoms that had undergone hybridization change depending on the kinetic energy added to the interlayer bond on the diamond surface.The energy values of the energy are adjusted to the simulated model of the 1916 atoms.The surface snapshots (a), (b), (c), and (d) are taken at the specific energy values added to the system visualized in OVITO [43].

Figure 8 .
Figure 8. Simplified illustration of emission from diamonds with (a) and without glass confinement (b).A schematic diagram describing the mechanism of the 975 nm CW laser multiphoton absorption and local geometry recombination (c).