Optical Storage Applications Research Articles

Reversible simulation and digital information storage and anti-counterfeiting applications in CaHfO3:Ho3+ photochromic materials

In the context of rapid development of the information age, photochromic (PC) materials have attracted significant interest due to their promising applications in erasable optical information storage and anti-counterfeiting technologies. This study presents a novel CaHfO3:Ho3+ PC material with a perovskite structure. Upon irradiation with ultraviolet (UV) light, the powder undergoes a color change from white to brown, and the resulting colored CaHfO3:Ho3+ can subsequently be bleached either by exposure to 365 nm light or through heat treatment. The incorporation of Ho3+ ions within the CaHfO3 matrix facilitates luminescence modulation via the PC effect. Information can be encoded through UV light irradiation, read using 254 nm light, and erased by 365 nm light or thermal processes. Notably, the stored information demonstrates remarkable stability over multiple cycles of "writing," "reading," and "erasing," exhibiting excellent fatigue resistance and reversibility. The coloration state can be maintained for at least 284 days, indicating that CaHfO3:Ho3+ materials possess significant potential for multifunctional applications in optical information storage and anti-counterfeiting technologies.

Multi-color photochromic waterborne polyurethane with high color fastness from hydroxyl-functionalized trichromatic spiropyrans

With advancements in smart materials, photochromic polyurethane (PU) shows considerable promise for applications in anti-counterfeiting, optical storage, and colorimetric sensing. However, significant challenges remain, such as reliance on solvent-based PU, poor color fastness due to blending methods, and limited color options, hampering its broader application. In response, this study selected trichromatic spiropyrans (SPs, SP-R, SP-Y, and SP-B) from preparing 14 hydroxyl-containing SPs. Under UV irradiation, SP-R, SP-Y, and SP-B can colorless transform to red, yellow, and blue, respectively. The photochromic waterborne polyurethanes (WPUs) were synthesized by incorporating trichromatic SPs as end-capping agents into WPU chains (denoted as CWPU-R/Y/B), exhibiting excellent photochromic performance. Unlike simple blending, the CWPU-R/Y/B process superior photochromic fatigue resistance (50 cycles), emulsion stability (6-month storage), solvent resistance, and color fastness (achieving the highest grade of 5), due to the covalent bonding effect. Furthermore, CWPU films with various colors were achieved through simple color mixing, providing a broader spectrum to meet diverse application needs. The potential application of CWPU in the anti-counterfeiting field was preliminarily explored, showing the gratifying results. This study presents a novel material applicable to the next generation of smart packaging, electronic information, and coatings.

Tunable and polarization-dependent electromagnetically induced transparency analogy in graphene-based terahertz metasurfaces

In this paper, we theoretically and numerically demonstrate a tunable and polarization-dependent electromagnetically induced transparency analogy based on graphene terahertz metasurfaces. The unit cell of the metasurface consists of three-layer graphene strips embedded in a silicon grating. The dynamic adjustment of the transparent window can be achieved by changing the coupling distance between the graphene layers and the polarization direction of the incident lights. The operation mechanism behind the phenomenon can be attributed to the near-field interaction and electromagnetic coupling of modes in graphene strips. Furthermore, the full wave electromagnetic simulations obtained by the finite-difference time-domain method agree well with the theoretical fitting results based on the three-harmonic oscillator model. In addition, by changing the Fermi levels, it can not only realize the outstanding slow-light effects with a maximum group index of 3750 but also obtain the four-frequency asynchronous optical switch function in terahertz regions. Therefore, our proposed metamaterial device may have potential applications in image switching, optical switches, slow-light device, optical communication, and optical storage.

Deep-trap ultraviolet persistent phosphor for advanced optical storage application in bright environments

Extensive research has been conducted on visible-light and longer-wavelength infrared-light storage phosphors, which are utilized as promising rewritable memory media for optical information storage applications in dark environments. However, storage phosphors emitting in the deep ultraviolet spectral region (200–300 nm) are relatively lacking. Here, we report an appealing deep-trap ultraviolet storage phosphor, ScBO3:Bi3+, which exhibits an ultra-narrowband light emission centered at 299 nm with a full width at half maximum (FWHM) of 0.21 eV and excellent X-ray energy storage capabilities. When persistently stimulated by longer-wavelength white/NIR light or heated at elevated temperatures, ScBO3:Bi3+ phosphor exhibits intense and long-lasting ultraviolet luminescence due to the interplay between defect levels and external stimulus, while the natural decay in the dark at room temperature is extremely weak after X-ray irradiation. The impact of the spectral distribution and illuminance of ambient light and ambient temperature on ultraviolet light emission has been studied by comprehensive experimental and theoretical investigations, which elucidate that both O vacancy and Sc interstitial serve as deep electron traps for enhanced and prolonged ultraviolet luminescence upon continuous optical or thermal stimulation. Based on the unique spectral features and trap distribution in ScBO3:Bi3+ phosphor, controllable optical information read-out is demonstrated via external light or heat manipulation, highlighting the great potential of ScBO3:Bi3+ phosphor for advanced optical storage application in bright environments.

Highly efficient and thermally stable photonic ceramic by controllable and full crystallization from glass

Polycrystalline ceramics are promising for a diverse range of applications in solid state laser, lighting, scintillator and optical storage. Unfortunately, current ceramic elaborations involves strict and complex synthetic procedures such as ultra-high pressure and vacuum processing. Here, we realize the tune of MgAl2Si4O12 and Mg2Al4Si5O18 phase formation in a glass by controlling the two crystal nucleation and growth individually, and obtain a polycrystalline non-stoichiometric Mg2-x/2Al4-xSi5+xO18:Eu2+ translucent ceramic by virtue of complete and congruent crystallization of the glass. Microstructural characterizations verify that the resulting ceramic exhibits dense and closely stacked micrometer-scale crystallites with very thin grain boundary structure. Chemical composition analysis by energy dispersive X-ray spectrometry revels the grain's composition is highly deviated from the stoichiometric Mg2Al4Si5O18, with atomic ratio Mg/Al/Si of 1.00: 1.46: 2.70. The precipitated non-stoichiometric Mg2-x/2Al4-xSi5+xO18, structurally having infinite channels z = 0.25 or 0.75 sites that run parallel to the c-aix, provides an robust crystal-field environment for Eu2+ 5d-4f transition. As a consequence, the ceramic produces intense emission with photoluminescence quantum yield (PLQY) up to 90 %, and excellent thermal stability emission with 70.1 % emission intensity at 420 K relative to that at room temperature, demonstrating it can be applied in high power lighting application with improved light quality by employing the ceramic as a color converter. Moreover, the ceramic also exhibits thermally stimulated luminescence at temperature reaching up to 700 K, originating from the deep electronic traps in Mg2-x/2Al4-xSi5+xO18 lattice with estimated trap depth of 0.73eV and 0.97eV. We also demonstrate the ceramic is hopeful for optical information storage application as the storage information can be retain well without vulnerable by the fluctuations of external environments due to the deep traps.

Multimodal anti-counterfeiting and optical storage application based on luminescence reversible modification and color change of photochromic phosphor

Reversible upconversion luminescence (RUCL) modification based on photochromism has received considerable interest due to its potential applications in optical storage and invisible optical anti-counterfeiting. Herein, white β-Ba2ScAlO5: Yb3+, Er3+ (β-BSAO-YE) phosphor was irradiated with 254 nm light, which caused the phosphor to turn blue due to the increase of oxygen vacancy. The blue β-BSAO-YE phosphor returns to its original color upon stimulation with 808 nm laser light or 125 °C, exhibiting a double photo-induced reversible photochromic change. The green and red upconversion luminescence (UCL) of the β-BSAO-YE were reversibly modified according to their photochromic properties. The UCL modification changes the luminescence color of the pattern, indicating that β-BSAO-YE phosphor is an ideal compound anti-counterfeit agent. The light information recorded on the β-BSAO-YE binary photochromic dot matrix can be read under ultraviolet (UV) and near-infrared (NIR) excitation, demonstrating the potential application of β-BSAO-YE phosphors as optical data storage media. In addition, the cyclic experiment showed good photochromic and UCL modulation repeatability. The new luminescent β-BSAO-YE not only proposes a new way to exploring upconversion red light materials, but also provides new materials for optical storage, optical information and optical anti-counterfeiting.

Observation of coupling interaction between surface plasmons and Tamm plasmons.

The optical effect analogous to electromagnetically induced transparency (EIT) in atomic systems has attracted broad attention in the field of photonics due to its promising applications in optical storage and integrated devices. Herein, we firstly report the experimental observation of the EIT-like effect generated from the coupling between surface plasmons (SPs) and Tamm plasmons (TPs) in a hybrid multilayer system at the near-infrared band. This multilayer system is composed of a nanofabricated silver grating on a silver/Bragg mirror with a SiO2 spacer. The experimental results show that a narrow reflection peak can appear in the wide reflection spectral dip due to the coupling between the SPs in the silver grating and TPs in the silver/Bragg mirror, which agree well with the finite-difference time-domain (FDTD) simulations. It is also found that the dip position of the EIT-like spectrum presents a redshift with the increase of the silver grating width. These results will provide a new way, to the best of our knowledge, for the generation of the EIT-like effect and light spectral manipulation in multilayer structures.

UV and X-ray induced photochromic material based on defect state exchanges

Inorganic photochromic (PC) materials are gaining increasing recognition as promising candidates for applications in optical storage and information display. However, conventional photochromic materials exhibit sluggish coding rates and a deficiency in intelligent response for writing and erasing under multiple excitation sources. This deficiency contributes to suboptimal readout/decoding efficiency and storage security. Here, we show a Ba2NaNb5O15:Er3+ photochromic material with photoluminescence reversible modulation that can fast respond to both ultraviolet light and 532 nm laser within about 1 s, which accompanied by thermal bleaching. The PC mechanism which is based on defect state exchanges between oxygen vacancy defects and color centers is attributed to the structural flexibility of Nb-O systems and oxygen vacancy increased under irradiation. More importantly, it shows differential PC decay behavior in response to X-ray and UV light due to the difference in the number of trapped carriers. Therefore, a simple strategy based on different self-recovery levels induced by double excitation is constructed to develop an encrypted optical memory model. This fast and differential excitation source response behavior hopefully stimulates the development of new encrypted optical memory.

Switchable image displays in tri-channel phase-change metasurfaces

Optical metasurfaces enable to manipulate light fields across multiple physical dimensions, significantly enhancing information density, security, and system integration. Here, we propose a general platform of multi-functional phase-change metasurfaces for dynamic image displays in the visible range, enabled by active manipulation of optical spectrum, amplitude, and phase, leading to threefold dynamic exhibition functions. Through elaborately encoding the tri-channel information using a single-cell metasurface composed of Sb2S3 nanobricks, three distinct functions are integrated and the flexibility of dynamic switch is allowed. Leveraging the tunable properties of Sb2S3 between amorphous and crystalline states, the switchable displays are realized, including a structural-color image, and grayscale and holographic images with independent-encryption polarization freedom. The proposed metasurfaces open new avenues in multi-functional meta-devices for optical storage, displays, and security applications.

Amorphous to Crystalline Phase Transformation Enables Tunable Persistent Luminescence for Multi‐Mode Optical Information Storage

AbstractMulti‐mode luminescence tuning through in situ crystallization of topological glass holds significance for photonics applications. Here, NaAlSiO4:Eu2+‐based glass ceramics are presented as stable persistent luminescence (PersL) materials by controlling the phase transformation in Eu2+ doped Na2O‐Al2O3‐SiO2 from amorphous glass to crystalline nepheline phase. X‐ray and UV excited PersL colors from blue to yellow are realized by adjusting the crystallization duration time, and trap statuses reveal the dynamic PersL process with a trap redeployment from 0.83 to 1.09 eV during the transformation. Optical information storage model is constructed with a structure of stacked emitting layers to enhance storage capacity. X‐ray excited luminescence time‐lapse imaging is further demonstrated with optical memory longer than 5 days. These findings advance the development of superior stable PersL glass ceramics and offer optical manipulation tactics for multi‐mode optical information storage applications.

Single femtosecond laser pulse-induced valence state conversion in BaFCl: Sm3+ nanocrystals for low-threshold optical storage.

Femtosecond laser-induced valence state conversion (VC) in solid materials has attracted significant research attention due to its potential application in ultra-high density optical storage, boasting advantages such as ultra-high recording speed, easy reading, and high signal-to-noise ratio. However, identifying appropriate materials and technological solutions conducive to efficient single-laser-shot recording remains a pivotal challenge for practical applications. In this work, we report single femtosecond laser pulse-induced VC in BaFCl: Sm3+ nanocrystals utilizing a 4F-configuration optical imaging system comprising two-dimensional scan galvo mirrors. For the first time, we experimentally reveal the luminescence mechanisms and channels of multiphoton absorption-induced Sm2+ ions under both single and multiple 800 nm fs laser pulses. Leveraging the highly efficient single femtosecond laser pulse induced VC, we demonstrate a prototype optical storage experiment by sweeping the recording laser pulse. Remarkably, a threshold pulse energy as low as ∼100 nJ for effective single-laser-shot recording in BaFCl: Sm3+ nanocrystals is obtained under the current experimental conditions. Our investigations offer profound insights into the physical mechanisms underlying femtosecond laser induced VC in solid materials, thereby promoting the prospects of VC based optical storage toward practical applications.

Manipulation of Upconversion Luminescence in Heavily Lanthanide‐Doped Halide Double Perovskites for Optical Information Storage

AbstractUpconversion (UC) process involves diverse energy levels and photoluminescence modes, however, it faces the challenge of concentration quenching of the doped lanthanide ions with multiple luminescence centers. Herein, Yb3+/Ho3+ and Yb3+/Tm3+ are heavily codoped into the lead‐free halide double perovskite single crystal Cs2NaErCl6, enabling the controlled energy transfer UC process, and accordingly, the UC materials exhibit anti‐concentration‐quenching owing to the defect tolerance characters. Depending on different doping couples, the UC materials show green and red emissions under the 980 nm laser excitations. Moreover, the green‐to‐red emission ratio in Yb3+/Tm3+ codoped Cs2NaErCl6 changes dynamically with the increasing pumping intensity due to the different sensitivities of the excited energy levels. This study provides a renewed direction of the lanthanide ions heavily‐doped halide double perovskites toward UC materials and facilitates the development of new smart luminescence materials for optical information storage applications.

Relationship between photochromism and persistent luminescence in barium-magnesium silicates

Photochromism and persistent luminescence (PersL) are two fascinating light-responsive effects in phosphors, both of which have found widespread applications in optical switching, optical anticounterfeiting and information storage. However, the relationship between photochromism and PersL has not been clarified, thus greatly limiting the use and design of the light-responsive materials in multifunctional applications. Herein, taking BaMgSiO4:Eu2+, TM (TM = transition metal: Fe, Co and Cr) as model materials, we first reveal that photochromism and PersL could be two independent photophysical effects, although they are both related to the charge carrier trapping/detrapping processes. Notably, photochromism and PersL show have different responses to light wavelengths, and the depth of traps involved in the two effects is also quite different. Moreover, by codoping different transition metal elements, we obtain the largest reflectance difference of ∼71 % among inorganic photochromic materials reported thus far, and demonstrate interesting multicolor photochromism, including magenta, golden and pink. Based on their distinct response to light and temperature, a multi-functionalized optical anticounterfeiting technology is proposed, which may open up a new avenue for applying the light-responsive materials in flexible electronics and wearable devices.

NIR regeneration and visible luminescence modification in photochromic glass: A novel encryption and 3D optical storage medium

AbstractPhotochromic glass shows great promise for 3D optical information encryption and storage applications. The formation of Ag nanoclusters by light irradiation has been a significant development in the field of photochromic glass research. However, extending this approach to other metal nanoclusters remains a challenge. In this study, we present a pioneering method for crafting photochromic glass with reliably adjustable dual‐mode luminescence in both the NIR and visible spectra. This was achieved by leveraging bimetallic clusters of bismuth, resulting in a distinct and novel photochromic glass. When rare‐earth‐doped, bismuth‐based glass is irradiated with a 473 nm laser, and it undergoes a color transformation from yellow to red, accompanied by visible and broad NIR luminescence. This phenomenon is attributed to the formation of laser‐induced (Bi+, Bi0) nanoclusters. We achieved reversible manipulation of the NIR luminescence of these nanoclusters and visible rare‐earth luminescence by alternating exposure to a 473 nm laser and thermal stimulation. Information patterns can be inscribed and erased on a glass surface or in 3D space, and the readout is enabled by modulating visible and NIR luminescence. This study introduces a pioneering strategy for designing photochromic glasses with extensive NIR luminescence and significant potential for applications in high‐capacity information encryption, optical data storage, optical communication, and NIR imaging. The exploration of bimetallic cluster formation in Bi represents a vital contribution to the advancement of multifunctional glass systems with augmented optical functionalities and versatile applications.image

Tunable effect on persistent luminescence via lithium-to-niobium ratio in LiNbO3: Pr polycrystals

This study has demonstrated that lithium niobate doped with praseodymium (LiNbO3:Pr), which initially did not exhibit persistent luminescence(PersL), can display significant PersL performance through the modulation of the lithium-to-niobium ratio (RLN). By adjusting the RLN to 1, LiNbO3:Pr achieved enhanced PersL, lasting several minutes, with the afterglow's duration further influenced by the RLN. Thermoluminescence (TL) assays and energy diagram analyses have elucidated that the presence and depth of oxygen vacancy defects are critical for both the emergence and longevity of PersL LiNbO3:Pr polycrystals. These insights enhance the understanding of PersL mechanisms in lithium niobate crystals and highlight their potential for application in optical information storage.

Reversible Multi-Mode Optical Modification in Inverse-Opal-Structured WO3: Yb3+, Er3+ Photonic Crystal.

Reversible optical regulation has potential applications in optical anti-counterfeiting, storage, and catalysis. Compared to common power materials, the reverse opal structure has a larger specific surface area and an increased contact area for optical regulation, which is expected to achieve higher regulation rates. However, it is difficult to achieve reversible and repeatable regulation of the luminescent properties of photonic crystals, especially with the current research on the structural collapse of photonic crystals. In this work, WO3: Yb3+, Er3+ inverse photonic crystals were prepared by the template approach, and reversible multi-mode optical modification was investigated. Upon heat treatment in a reducing atmosphere or air, the color of the photonic crystals can reversibly change from light yellow to dark green, accompanied by changes in absorption and upconversion of luminescence intensity. The stability and fatigue resistance of this reversible optical modification ability were explored through cyclic experiments, providing potential practical applications for photocatalysis, optical information storage, and electrochromism.

Improved optical contrast of plasmonic phase change memory using a Fabry-Perot cavity

As a promising technology to realize multilevel, non-volatile data storage and information processing, optical phase change technologies have attracted extensive attention in recent years. However, existing phase-change photonic devices face significant challenges such as limited switching contrast and high switching energy. This study introduces an innovative approach to tackle these issues by leveraging Fabry-Perot (F-P) cavity resonance and plasmon resonance techniques to enhance the modulation effect of phase change materials (PCMs) on the light. To the best of our knowledge, a novel device structure is proposed, featuring an elliptic nano-antenna placed on an F-P cavity waveguide composed of symmetric Bragg grating. This design exploits the enhanced electric field to achieve low power consumption and high contrast. The device enables crucial functions, including read, write, and erase operations, under all light conditions. Through the synergistic utilization of plasma and F-P cavity effects, an ultra-high switching contrast of around 70.6% is achieved. By varying the pulse power or duration, the proportion between the crystalline and amorphous states of the PCMs is altered, consequently modifying its refractive index. With its wide range of applications in optical storage and computing, the device holds significant potential for advancing these fields.

Ultraviolet-B and Near-Infrared Dual-Band Luminescence in Bi3+/Bi2+ Codoped Persistent Phosphor for Optical Storage Application.

Discovering multifunctional luminescent materials to meet the demands of modern spectroscopy is of great significance. However, it is a standing challenge to enable multiple luminescence properties in a single material system via single metal ion doping. Here, we report the inherently Bi3+/Bi2+ codoped Ca3Ga2Ge3O12 persistent phosphor where Bi3+ is in situ reduced to Bi2+. This phosphor can act as an efficient multimodal luminescence material, which simultaneously exhibits long-lasting (>12 h) ultraviolet-B (UVB) and near-infrared (NIR) dual-band persistent luminescence after irradiation by 254 nm ultraviolet (UV) light. UVB and NIR afterglow are ascribed to the distinct Bi3+ and Bi2+ emitters, respectively, proven by comprehensive spectroscopic investigations including X-ray absorption near-edge structure spectra and X-ray photoelectron spectroscopy. Besides, this phosphor also exhibits exceptional photochromic features, accompanied by a rapid body color transformation from white to brown in response to 254 nm UV light within 60 s and excellent recovery capacity upon thermal or blue/white light stimulation. The combination of UVB persistent luminescence of Bi3+ and NIR afterglow of Bi2+ coupled with reversible white-to-brown photochromism phenomenon offers one type of promising multifunctional luminescence material, showing potential to be used for optical storage and anti-counterfeiting applications.

Development of High-Performance Polyindole/Silicon Carbide Nanocomposites for Optoelectrical and Sensing Applications.

In this study, silicon carbide (SiC)-reinforced polyindole (PIn) nanocomposites were prepared by a simple in situ polymerization method. The successful reinforcement of the nanofiller within the host matrix was characterized using different analytical techniques. The chemical bonding of SiC in the polymer was identified by the characteristic peak around 800 cm1 using Fourier transform infrared spectroscopy (FT-IR). The increment in intensity of the absorption and enhanced crystallinity of the samples upon the addition of nanofillers were analyzed using UV-vis spectroscopy and X-ray diffraction (XRD). The prepared specimens showed reduced optical bandgap energy (3.188 eV) and Urbach energy (2.315 meV) with an improved refractive index (2.348). The effect of nanoparticles on the surface morphology of the nanocomposites was studied using scanning electron microscopy (SEM), and a uniform dispersion of fillers in the matrix was found for PInSiC7. A high-resolution transmission electron microscopy (HR-TEM) revealed the shape and average particle size of the sample. X-ray electron spectroscopy (XPS) measurements confirmed the formation of the nanocomposite by exhibiting the presence of all elements in the corresponding spectra. The thermal stability and glass transition temperature of the nanocomposites were significantly improved with the addition of SiC. The temperature-dependent AC conductivity, dielectric parameters, complex impedance, and electrical modulus were also evaluated using an impedance analyzer. The increased electrical characteristics of the PInSiC7 sample can be attributed to the uniform spread and strong synergetic interaction of SiC with PIn. The results thus showcased the potential of the samples for use in optical and energy storage applications. This study was also extended to understand the ammonia sensing properties, which make it possible to design and develop gas sensors using the PInSiC nanocomposites.

Designing Photochromic Materials La2MgSnO6:Er,Fe with Dynamic Luminescence Modulation for Dual‐mode Optical Information Reading

AbstractInorganic photochromic luminescent materials hold immense promise as potential candidates for optical information storage applications. Unfortunately, static and single reading mode of photochromic luminescent materials in bright and dark environments pose a security threat to the stored information. Here, a novel material La2MgSnO6:Er3+,Fe3+ is developed, possessing both reversible photochromic and adjustable upconversion/downconversion photoluminescent (PL) properties. Upon exposure to 275 nm ultraviolet (UV) light, the sample changes in color from white to brown. And this transformation rapidly reverses when exposed to 365 nm UV light, resulting in a corresponding alteration in luminescence intensity. Notably, when combined with photochromic, the 980 nm excited upconversion PL maintains stable luminescence, while the 365 nm excited downconversion PL exhibits significant intensity changes. Inspired by this unique feature, a dark‐field selective dual‐mode reading is proposed that depends on the excitation wavelength, including static decrypt in long‐time cases and dynamic reading in time‐limited situations. These findings have the potential to revolutionize high‐security data storage applications and drive advancements in the field.