Defect cluster engineering in ZnGa2−x(Mg/Ge)xO4:Cr3+ nanoparticles for remarkably improved NIR persistent luminescence

Recently, study on Cr³⁺-doped zinc gallate and zinc gallogermanate persistent phosphors has become a hot topic in persistent luminescence and bio imaging areas, because of their near infrared (NIR) emission and long afterglow. However, regulation of efficient traps and improvement of persistent luminescence through bottom-up design are the key challenge. Here, we recommend a new paradigm of chemical unit co-substitution with [Mg²⁺-Ge⁴⁺] substituting for [Ga³⁺-Ga³⁺] in ZnGa₂O₄, which contributes to the opposite charged and distorted octahedral defects of Mg_Ga′ and Ge_Ga ^· in pair around the Cr_N2 ions. The formed defect clusters of Mg_Ga′-Cr_N2-Ge_Ga ^· , which are closely related to the trap depth, can be accurately regulated through varying the doping content of Mg²⁺/Ge⁴⁺ in the resulting spinel solid solutions of ZnGa_2−x(Mg/Ge)_xO₄:Cr³⁺ (x = 0–1.25). Moreover, the defect clusters cannot only store and recharge visible and UV radiations that contributes to the long lasting NIR persistent luminescence but also can enhance the NIR emission intensity at ~695 nm. The persistent luminescence induced by UV light excitation exhibits an improvement at a deeper trap depth, but it follows an opposite law through visible light excitation. The prepared nanoparticles have the advantages of intense NIR emission, long lasting afterglow, and excellent rechargeability for visible/UV radiations, so they are the potential nanoprobes for long-term bio imaging in living animals.     

New insights into phosphorescence properties of LuAGG: Long afterglow phosphor-in-glass for optical data storage

Newly long afterglow phosphor-in-glass (PiG) plays pivotal roles in the region of optical data storage. By using solid-phase reactions and unique spectrum modulation methods, a color-tunable PiG with decent persistent phosphorescence which can be tuned from green to blue has been fabricated. Lu₃Al₂Ga₃O₁₂: Ce³⁺, Cr³⁺ (LuAGG: Ce³⁺, Cr³⁺) based on TBZNA glass could emit bright green light signal located at 350 and 420 nm ascribed to the 5d₁/5d₂-4f transitions when corresponding optical data was being loadout. The doping of Cr³⁺ increases the density of the trap and provides additional traps between the shallow trap and the deep trap to capture more electrons, further improving afterglow decay time. And the storage time and cyclic reading times are derived by the method of thermal stimulation. Thereinto, tunable emission color has been obtained via changing the concentration of Ga³⁺, using UV excitation. Moreover, the influence of the Cr³⁺/Ga³⁺ on luminescence properties of long-afterglow-PiG materials have been described in detail. Achieved results confirm that it makes LuAGG-PiG as a long afterglow PiG matrix, demonstrating its promising application in optical data storage.     

Doping and luminescence mechanisms of broadband NIR-II emitting Zn2(1−x)Ni2xGa3Ge0.75O8 nanoparticles

In this study, Zn_2(1−x)Ni_2xGa₃Ge_0.75O₈ (x = 0.0002, 0.001, 0.002, 0.010, 0.020, and 0.030) nanoparticles with broadband NIR-II emissions were synthesized by a hydrothermal synthesis combined with a vacuum annealing. For the Ni²⁺-doped ZGGO samples (x = 0–0.03), with increasing concentration, the particle shape gradually becomes spherical and the average particle size decreases from 124.4 to 74.2 nm. Meanwhile, for the ZGGO:Ni²⁺_0.01 nanoparticles, the asymmetrically broad emission peak around 1290 nm, which is the superposition of the two peaks locating at 1280 and 1450 nm, can be observed and the afterglow time exceeds 30 min. Based on the spectral data, luminescence decay curves, first-principles calculations, and Tanabe–Sugano theory, it is found that Ni²⁺ ions can occupy not only tetrahedral but also octahedral Zn²⁺ sites (locating in anti-site defects pair) in the spinel ZGGO host, and they have the contributions to the 1450 and 1280 nm emission peaks, respectively. Furthermore, the surface-modified ZGGO:Ni²⁺ nanoparticles exhibited good stability in the H₂O and HSA (5% human serum albumin, pH = 7.4) solutions and the occurred agglomeration sinking in the SLS (simulate lysosomal solution, pH = 4.7) solution. Compared to the narrow-band NIR-II emitting persistent luminescence nanoparticles (ZGGO:Cr³⁺,Er³⁺ and ZGGO:Cr³⁺,Nd³⁺), broadband NIR-II emitting persistent luminescence nanoparticles (ZGGO:Ni²⁺ NIR-II) possess stronger persistent luminescence intensity and can effectively avoid the water absorption of biological tissues. Our results suggest that ZGGO:Ni²⁺ persistent luminescence nanoparticles have a potential to become optical probes for deep-tissue autofluorescence-free bioimaging in the biomedical field.     

Near infrared persistent luminescence of transparent Zn-Ga-Ge-O:Cr3+ glass ceramic for optical information storage

Cr³⁺-doped near-infrared (NIR) afterglow phosphors have received wide recognition in the optical storage field because of the high signal-to-noise ratio and broad excitation spectra. In this article, the high-temperature TL intensity of ZnGa₂O₄:Cr³⁺ afterglow glass ceramic (ZGO:Cr³⁺ GC) was enhanced via partial hetero-valence substitution of Ge for Ga, demonstrating the tunability of the trapped electron levels in ZGO:Cr³⁺ GC. The persistent luminescence phosphor ZGO:Cr³⁺ GC exhibits a zero-phonon lines emission peaking at 698 nm, attributing to the ²E→⁴A_2g transition of Cr³⁺ ions. Moreover, the trap levels in Zn-Ga-Ge-O:Cr³⁺ glass ceramic (ZGGO:Cr³⁺ GC) are deeper than those of the Ge-free one and the captured electrons in deeper levels cannot be released only by the ambient thermal energy, thus the optical storage capacity of ZGGO:Cr³⁺ GC is much larger. By means of an additional 980 nm laser photostimulation, an intense NIR emission could be obtained. In consequence, ZGGO:Cr³⁺ GC has a promising application prospect in optical information storage field.     

Highly efficient photostimulated luminescence of Pb2+ doped SrAl2O4:Eu2+, Dy3+ borate glass for long-term stable optical information storage

Despite the transformative role in society, information storage materials remain vulnerable to the corrosion by water, oxygen and heat, while topological engineering of glass provides an attractive solution to this tricky problem. Here, a considerable discovery is reported that the doping of Pb²⁺ ions could greatly affect the luminescence behavior of SrAl₂O₄:Eu²⁺, Dy³⁺ borate glass, resulting in a controllable property between long persistent luminescence and photostimulated luminescence. Specifically, high concentration Pb doped samples featuring the deeper continuously distributed trap levels with 0.97–1.47 eV performed highly efficient photostimulated luminescence. In other words, the ultraviolet-visible photons could be “written” in the deeper traps and then “read out” under the stimulation of a 980 nm near-infrared laser. From the combined structural and luminescence characterizations, it was speculated that the deeper trap originated from the increase of oxygen vacancies at defect levels. The practical anti-counterfeiting application was successfully realized based on this material with superior photostimulated luminescence phenomenon, which rendered the SrAl₂O₄:Eu²⁺, Dy³⁺ borate glass shine in a new field such as anti-counterfeiting, yet as a promising candidate for information storage application.     

Orange-red persistent luminescence in Mn2+-Doped Sr3Y2Ge3O12 films for dynamic anti-counterfeiting

The research focus in the field of anti-counterfeiting has shifted toward the secure luminescent label technology, which has gained prominence. The exceptional luminescence properties of persistent luminescence materials are important in the achievement of effective anti-counterfeiting measures. It is in this context that Sr₃Y₂Ge₃O₁₂ can serve as an excellent matrix material. In this study, it is found that Sr₃Y₂Ge₃O₁₂: 4.00% Mn²⁺ exhibits a luminescence intensity, persistence time, and stability that meet the practical requirements for applications. It is shown that the fabricated persistent luminescence film can be used in anti-counterfeiting applications, thereby, demonstrating the possibility to broaden the application scope of persistent luminescence materials. An emission band centered at 634 nm and a high-energy inflection point at 578 nm are observed in the samples excited at 260 nm. Fluorescence emission at 634 nm is also achieved through X-ray excitation. Through thermoluminescence, photoluminescence, and phosphorescence spectroscopy, a comprehensive investigation of the trap characteristics and inherent mechanisms of the long persistent phosphorescence has been conducted. The novel orange-red Sr₃Y₂Ge₃O₁₂: Mn²⁺ phosphor is extensively examined.     

Synthesis,Crystal Structure,and Enhanced Luminescence of Garnet‐Type Ca3Ga2Ge3O12:Cr3+ by Codoping Bi3+

Garnet‐type compound Ca₃Ga₂Ge₃O₁₂ and Cr³⁺‐doped or Cr³⁺/Bi³⁺ codped Ca₃Ga₂Ge₃O₁₂ phosphors were prepared by a solid‐state reaction. The crystal structure of Ca₃Ga₂Ge₃O₁₂ host was studied by X‐ray diffraction (XRD) analysis and further determined by the Rietveld refinement. Near‐infrared (NIR) photoluminescence (PL) and long‐lasting phosphorescence (LLP) emission can be observed from the Cr³⁺‐doped Ca₃Ga₂Ge₃O₁₂ sample, and the enhanced NIR PL emission intensity and LLP decay time can be realized in Cr³⁺/Bi³⁺ codped samples. The optimum concentration of Cr³⁺ in Ca₃Ga₂Ge₃O₁₂ phosphor was about 6 mol%, and optimum Bi³⁺ concentration induced the energy‐transfer (ET) process between Bi³⁺ and Cr³⁺ ions was about 30 mol%. Under different excitation wavelength from 280 to 453 nm, all the samples exhibit a broadband emission peaking at 739 nm and the intensity of NIR emission increases owing to the ET behavior from Bi³⁺ to Cr³⁺ ions. The critical ET distance has been calculated by the concentration‐quenching method. The thermally stable luminescence properties were also studied and the introduction of Bi³⁺ can also improve the thermal stability of the NIR emission.     

Luminescence enhancement of Cr3+ doped garnet phosphor for high-performance LED towards smart NIR light source

Cr³⁺ doped phosphor shows great potential for near-infrared (NIR) light-emitting diodes (LED), but it suffers from low quantum efficiency and poor thermal stability. Herein, a novel Cr³⁺ doped broadband NIR garnet Ca₃Sc₂Ge₃O₁₂ phosphor was developed. The multisite structure of the emission band is investigated by site-selective spectroscopy and is attributed to the octahedral Cr³⁺ perturbed by defects. Moreover, we propose different strategies to enhance the luminescence of the phosphor, including enhancement of crystallinity and elimination of defects. Compared with the initial sample, the emission intensity of the optimized phosphor is improved for 8.6 times. The optimal Ca₃Sc₂Ge₃O₁₂: 0.06Cr³⁺ phosphor exhibits excellent thermal stability. At 423 K, the integral emission intensity of the optimal sample remains 94.7% of that at room temperature. Finally, high-performance NIR LED was fabricated using a blue LED and the title phosphor. The packaged LED lamp has high radiance (109.3 mW@300 mA) and photoelectric efficiency (15.96%@40 mA). Our study not only provides a boulevard for enhancing the luminescence of Cr doped NIR phosphor, but also gives a new perspective for understanding the multisite luminescence of Cr³⁺ in garnet host.     

Broadband near-infrared double-perovskite phosphor Sr2ScTaO6:Cr3+, Yb3+ for NIR pc-LED applications

The broadband near-infrared (NIR) phosphor converted light emitting diode (NIR pc-LED) has garnered unprecedented attention due to its crucial role in NIR applications. However, there remains a scarcity of efficient broadband NIR luminescence materials capable of emitting NIR light with wavelengths greater than 800 nm. This study reports the synthesis, crystal structure and photoluminescence (PL) properties for double perovskite Sr₂ScTaO₆:Cr³⁺ phosphors which exhibit a broadband NIR emission in the 650–1250 nm range, peaking at∼815 nm with the full width at half maximum (FWHM) of 161 nm. The observed broadband emission arises from two distinct Cr³⁺ centers, namely Sc³⁺ and Ta⁵⁺ octahedral sites within the Sr₂ScTaO₆ structure, as demonstrated by luminescence and decay kinetic analysis. A significant enhancement of the thermal stability and a remarkable broadening of the FWHM (from 161 to 275 nm) are achieved by employing Yb³⁺ co-doping strategy. The efficient energy transfer from Cr³⁺ to Yb³⁺ was confirmed through emission and excitation spectra, as well as luminescence decay measurements. Finally, Sr₂ScTaO₆:Cr³⁺-Yb³⁺ phosphor was integrated with a 470 nm blue LED chip to fabricate a NIR pc-LED device, and its potential application in night vision was evaluated.     

Enhanced afterglow behavior of a new Eu2+: NaBa4(BO3)3 yellow phosphor co-doped with different cations Dy3+, Ho3+and Nd3+

A new Eu²⁺: NaBa₄(BO₃)₃ phosphor, synthesized under conventional solid state approach, exhibits bright yellow persistent luminescence with the co-doping of Eu²⁺, Ln³⁺ (Ln = Dy³⁺, Ho³⁺, Nd³⁺). XRD investigation reveals that all samples are pure phase phosphors with cubic structure, indicating the doped Eu²⁺and Ln³⁺ cations were incorporated into the lattice that did not form inclusive phase in the material. Since there are two coordination forms ([EuO6] and [EuO8]) of Eu²⁺ cations in the matrix, the above yellow luminescence can be divided into two different emissions centering at 558 nm and 627 nm, confirming the crystallographic environment on the photoluminescence from Eu²⁺ center. Optimal doping concentrations for each cations were further determined as 2% atm for Eu²⁺, 2% atm for Dy³⁺, 3% atm for Ho³⁺ and 2% atm for Nd³⁺. Afterglow behaviors are also observed for samples with Ln³⁺ co-doping, which reveal typical double exponential decay model. Among the phosphors synthesized, the sample 2 at%Eu²⁺/3 at%Ho³⁺: NaBa₄(BO₃)₃ displays the best performance with higher initial brightness and longer lifetime, which can be attributed to the formation of electron traps with high concentration and suitable energy level, as confirmed by the result from thermal stimulated luminescence (TSL) analysis.     

A building-block strategy for dynamic anti-counterfeiting by using (Ba,Sr)Ga2O4:Sm3+ new red persistent luminescent phosphor as an important component

Long persistent luminescence materials developed to commercial standards are primarily concentrated in the blue and green regions, with only a few in the red region. Red, as one of the three basic colors, can be mixed in various proportions with blue and green to yield various colors. The development of red persistent phosphors has a broader application potential but remains a challenge. A solid-state reaction method was used to synthesize new red persistent luminescent materials of Ba_1-xSr_xGa₂O₄:Sm³⁺ (x = 0–0.09). In BaGa₂O₄, both Sr²⁺ and Sm³⁺ preferentially occupy the Ba²⁺ site rather than the Ga³⁺ site. When exposed to UV light at 254 nm, the phosphors emit the characteristic red emission of Sm³⁺ at wavelengths ranging from 500 nm to 750 nm. After removing the UV light source, an intense red afterglow that lasted more than 1400 s was observed. The red afterglow signal reappears after a heating process. Doping Sr²⁺ reduces the trap depth and improves the red persistent luminescence significantly. Because the escaped electrons from traps compensate for the emission loss of Sm³⁺ during the heating process, the red phosphors have unimaginably luminescent thermal stability. Thus, the emission intensity at 200 ^°C is 1.6 times that at room temperature. The prepared red persistent phosphors show multimode luminescence, with the output signal being time and temperature sensitive, indicating that they are potential luminescent materials for anti-counterfeiting applications. Finally, a building-block strategy for advanced anti-counterfeiting applications of dynamic display information is proposed, with red persistent phosphors serving as an important component combined with upconversion phosphors of NaYF₄:Yb³⁺, Tm³⁺, and green persistent phosphors of SrAl₂O₄:Eu²⁺, Dy³⁺.     

Synthesis and Persistent Luminescence Mechanism of a Novel Orange Emitting Persistent Phosphor Sr5(BO3)3Cl:Eu2+

A series of Eu²⁺‐doped Sr₅(BO₃)₃Cl phosphors were prepared successfully using a conventional solid‐state reaction method. The luminescent properties were studied systematically by utilizing photoluminescence spectra, decay curves, persistent luminescence spectra, and thermoluminescence glow curves. Energy transfer from host to emission center Eu²⁺ was affirmed. The orange persistent luminescence emission was observed for the first time. The optimal doping concentration of Eu²⁺ for persistent luminescence was experimentally to be approximately 0.5% and the orange persistent luminescence duration can persist about 15 min. On the basis of the experimental results, a model was constructed and the relevant mechanism of persistent luminescence was illustrated in detail. Two different ways of trapping the charge carriers were also discussed.     

Oxidative Dehydrogenation of Propane with CO2 Over Cr/H[B]MFI Catalysts

Abstract  

Cr/silicalite-1 and Cr/H[B]MFI catalysts were prepared by the impregnation method, and Cr/H[B]MFI were further treated by steaming. The catalysts were employed for the oxidative dehydrogenation of propane to propylene with CO₂ as the oxidant. Cr/H[B]MFI showed significantly higher catalytic activity than Cr/silicalite-1, and steamed Cr/H[B]MFI was superior in the reaction stability to Cr/H[B]MFI. The nature of the supported chromium species have been characterized by a number of physicochemical techniques, such as Raman, UV–vis and NMR. It is concluded that the steaming led to the auto-reduction of some Cr⁶⁺ to Cr³⁺, and resultant Cr³⁺ species might be located near the boron center in the borosilicate framework to counterbalance the negative charge of the framework. The transformation of Cr⁶⁺ species to Cr³⁺ species, facilitated by the steaming process and the presence of boron in the catalyst, is responsible for the enhanced stability of oxidative dehydrogenation of propane to propylene with carbon dioxide as the oxidant.     

Tuning the luminescence properties of blue and far-red dual emitting Gd2MgTiO6: Bi3+, Cr3+ phosphor for LED plant lamp

Blue and far-red light play a key role in plant growth, so it is necessary to develop blue and far-red dual emitting phosphors. However, the match between phosphors and plant pigments is not satisfactory. In this work, we synthesized a series of blue and far-red dual emission Gd₂MgTiO₆: Bi³⁺, Cr³⁺ (GMTO: Bi³⁺, Cr³⁺) phosphors and discussed the luminescence performance. The blue emission at 430 nm is ascribed to ³P₁ → ¹S₀ transition of Bi³⁺ and the far-red emission is ascribed to ⁴T₂ → ⁴A₂ and ²E → ⁴A₂ transitions of Cr³⁺. Notably, because of the energy competition between Cr³⁺ ions and host materials, the luminescence tuning realized with the content of Cr³⁺ doping. In addition, an energy-transfer performance occurred from Bi³⁺ ions to Cr³⁺ ions and the photoluminescence intensity of Cr³⁺ can be enhanced by Bi³⁺. The pc-LEDs devices were synthesized by GMTO: Bi³⁺, Cr³⁺ phosphor, and ultraviolet (UV) chips. Finally, the emission of GMTO: Bi³⁺, Cr³⁺ phosphor matched well with the absorption spectra of plant pigments which indicated the potential applications in LED plant lamp.     

Trap engineering in ZnGa2O4:Tb3+ through Bi3+ doping for multi-modal luminescence and advanced anti-counterfeiting strategy

Optical information encryption based on luminescence materials have received much attention recently. However, the single luminescence mode of the luminescence materials greatly limits its anti-counterfeiting application with high safety level. Here, a series of luminescence materials of Tb³⁺ and Bi³⁺ co-doped ZnGa₂O₄ phosphors with great correspondence in photoluminescence (PL), persistent luminescence (PersL), and thermoluminescence (TL) modes was synthesized by the conventional solid-phase method for the application in multi-modal anti-counterfeiting fields. Under the excitation of 254 nm, ZnGa_1.99O₄:0.01 Tb³⁺, yBi³⁺ (y = 0.001,0.002) sample exhibited a broad blue emission band (the transition from [GaO₆]) at 440 nm and the characteristic emission peaks of Tb³⁺ at 495 nm, 550 nm, 591 nm and 625 nm, corresponding to the transitions of ⁵D₄-⁷F_n (n = 6, 5, 4, 3), respectively. Interestingly, the co-doping of Bi³⁺ ions improve the crystallinity and particle size of the phosphor, subsequently enhanced the PL intensity of Tb³⁺ to 6 times that of Tb³⁺ singly doped ZnGa₂O₄ phosphor. Further, the flexible films with multi-modal luminescence properties have been fabricated through the unique TL and PersL characteristics of ZnGa₂O₄: Tb³⁺, Bi³⁺ phosphors, including “Optical information storage film”, “snowflake and characters” and “QR code”. Moreover, a set of optical information encryption is obtained by combining ZnGa₂O₄:Tb³⁺, Bi³⁺ phosphor and red emitting phosphor. The results indicate that ZnGa₂O₄:Tb³⁺, Bi³⁺ phosphor with multi-modal stimulus response can be expected to be potentially used in the applications of optical information storage and anti-counterfeiting fields.     

A novel far-red phosphors Li2ZnTi3O8:Cr3+ for indoor plant cultivation:Synthesis and luminescence properties

A novel far-red phosphors Li₂ZnTi₃O₈:Cr³⁺ were successfully synthesized via the conventional solid-state method. The structural characteristics, luminescence properties and concentration quenching of the Li₂ZnTi₃O₈:Cr³⁺ phosphors were investigated systematically. Under the excitation at 360 nm and 468 nm, the Li₂ZnTi₃O₈:Cr³⁺ phosphors displays the emission spectra in the range from 600 nm to 850 nm. The far-red emission centered at 735 nm was attributed to the spin-forbidden ²E→⁴A₂ transition of Cr³⁺ ions. The research results of this paper indicate that the phosphors Li₂ZnTi₃O₈:Cr³⁺ has prospective applications in indoor plant cultivation.     

Novel Self‐Activated Zinc Gallogermanate Phosphor: The Origin of its Photoluminescence

Since 2012, zinc gallogermanate has drawn interests as an excellent host phosphor for a variety of dopants (e.g., Cr³⁺, Bi³⁺ and Mn²⁺). However, the origin of its self‐activated luminescence has been largely unknown. Here, zinc gallogermanate of the composition Zn_1+xGa_2?2xGe_xO₄ (0 ≤ x ≤ 1) is prepared by solid‐state reaction, and the evolution of the crystal structure with the composition is studied. The phosphors show a broad white‐bluish emission upon excitation by ultraviolet (UV) light, and the luminescence intensity greatly increases as Ga³⁺ are substituted by Ge⁴⁺. A full spectrum of the defects and trap centers responsible for the luminescence is given by a multiple characterization methods, such as low temperature electron spin resonance, positron annihilation lifetime and thermoluminescence spectra. The results show that the zinc gallogermanate is a promising self‐activated phosphor for a variety of applications.     

Tunable trap depth for persistent luminescence by cationic substitution in Pr3+:K1−xNaxNbO3 perovskites

The development of efficient red-emitting persistent phosphor is still an ongoing challenge. In the search of persistent materials in red range, Pr³⁺ is a good candidate owing to its transitions between ¹D₂ and ³H₄ state at about 612 nm. In this paper, we investigated the red persistent properties of Pr³⁺-doped perovskite oxide ABO₃, (A: K, Na and B: Nb), which can be elaborated as large single crystal. KNbO₃:Pr³⁺ appears to have weak photoluminescence and no persistent luminescence. However, the cationic substituted compounds K _{1− x} Na _x NbO ₃ :Pr³⁺ (x = 0, 0.4, 0.5, 0.7 0.9, 1) exhibit intense persistent luminescence, which increases steadily with increase in Na content. We correlated persistence behavior with the position of Metal-to-Metal Charge Transfer (MMCT) band, which plays crucial role in tuning of the trap depth. The MMCT band position decreases with the addition of Na contents and the thermoluminescence peak shifts toward higher temperature indicating the formation of deeper traps. This is in good agreement with the enhancement of the persistent luminescence suggesting that a proper tailoring of MMCT is needed to design efficient Pr³⁺-persistent phosphors with better performance. A detailed analysis on the trap depth, bandgap energy, and persistent luminescence properties is reported tuning the composition in the K _{1− x} Na _x NbO ₃ :Pr powder.     

Order-disorder structural transition in Pr3+-doped Ba3Ga2O6 for rewritable and write-once-read-many optical data storage

The emerging challenges of the big data era, both in storage density and security, require the development of the next-generation optical data storage materials. Here, we report for the first time a photo-stimulated luminescence (PSL) material, Ba₃Ga₂O₆: Pr³⁺, for rewritable optical storage and write-once-read-many data preservation. Ba₃Ga₂O₆: Pr³⁺, with an isolated deep trap depth in the range 1.26–1.53eV, has been used for data encoding/decoding under the excitation of 254 nm UV light and by the simulation of an 808 nm NIR laser. Meanwhile, the phosphor allows for high-security write-once-read-many optical memory by taking advantage of the irreversible change of the photoluminescence (PL) color from blue to green (a binary blue ‘0’ and green ‘1’ code) irradiated by 365 nm UV light. The comprehensive investigations indicate that the irreversible PL switching is as a result of the order-disorder structural transition by thermal treatment. The new persistent luminescence material not only exhibits promising applications in sustainable rewritable data storage, but also paves the way for write-once-read-many optical information storage with a high level of security.     

Improving the luminescence and afterglow properties of Mg3Y2Ge3O12:Cr3+ by co-doping Bi3+

Generally, the emission intensity and afterglow of the near infrared phosphors can be improved by co-doping the sensitizer. In this work, Bi³⁺ ions as sensitizer are introduced into the near infrared phosphor Mg₃Y₂Ge₃O₁₂:Cr³⁺, and the luminescence properties are investigated. According to the principle of radius adaptation, Bi³⁺ ions would occupy eight coordinates in the host instead of Y³⁺ and Mg²⁺. Through structural refinement, theoretical calculation and experimental phenomena, there are two kinds of luminescent sources for Bi³⁺ ions, which come from ³P₁ → ¹S₀ (441 nm) and MMCT (330 nm), respectively. In addition, the substitution of Bi³⁺ for Mg²⁺ will result in inequivalent substitution forming defects (Bi_Mg·), and the trap depth is 0.55 eV. For Bi³⁺ and Cr³⁺ co-doped Mg₃Y₂Ge₃O₁₂, there are two factors can that can affect the luminescent properties of Cr, which are energy transfer and defects. The samples are obtained with three times the original emission intensity with the introduction of defects. At the same time, Bi³⁺ ions capture electrons to form new electron traps Bi²⁺ (Bi³⁺ + e^-) and the trap depth is 0.81 eV. Therefore, under the action of two traps Bi_Mg· and Bi²⁺ (Bi³⁺ + e^-), the afterglow characteristics of the samples are improved and the time can reach 1.5 h.