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.     

Mn2+/Pr3+/Tb3+ single-doped Mg4Ga4Ge3O16 persistent luminescence materials for optical information storage application

Persistent luminescence (PersL) phosphors are considered as promising candidates for the next generation of information storage medium. Mg₄Ga₄Ge₃O₁₆ (MGG) is an electron trapping material which exhibits defect luminescence, and the luminescent properties are easily tuned via doping various activated ions. In this work, undoped and Mn²⁺/Pr³⁺/Tb³⁺ single-doped MGG phosphors were synthesized via high temperature solid phase reactions. X-ray diffraction and scanning electron microscope results confirm that the activated ions tend to occupy Mg²⁺ sites. Excited at 265 nm, the MGG host exhibits a defect emission band peaked at 450 nm. Red, pink and green emissions are observed in the Mn²⁺/Pr³⁺/Tb³⁺ single-doped MGG samples, which are ascribed to the Mn²⁺: ⁴T₁(G) → ⁶A₁(S), Pr³⁺: ¹D₂ → ³H₄ and Tb³⁺: ⁵D₄ → ⁷F₅ transitions, respectively. All the samples exhibit bright PersL for minutes after the cessation of excitation. The energy transfer, concentration quenching, luminescence decay and afterglow mechanisms are also discussed in detail. The phosphors exhibit efficient thermal and optical stimuli response, showing great potentials in the optical information storage.     

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⁺.     

Polarization‐Induced Photoluminescence Quenching in (Ba0.7Ca0.3TiO3)–(BaZr0.2Ti0.8O3):Pr Ceramics

Pr³⁺‐doped (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)TiO₃ ceramics were prepared by a solid‐state reaction method. The effects of doping concentration, sintering temperature, and ferroelectric remanent polarization on photoluminescence (PL) properties of samples were systematically investigated. The PL spectra of samples exhibit strong green and red emissions with a broad blue excitation band ranging from 430 to 500 nm, in a good agreement with all commercial blue LEDs emission wavelength. Except for the concentration and temperature PL quenching, the polarization‐induced PL quenching was obviously observed, and the degree of PL quenching changes with Pr³⁺ concentrations, the origin of the change is well interpreted by field‐induced structural phase transitions between rhombohedral (R3m) and tetragonal (P4mm) for BCZT: xPr ceramics near the morphotropic phase boundary.     

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.     

Long persistent and photo‐stimulated luminescence in Pr3+‐doped layered perovskite phosphor for optical data storage

As the time for big data is coming, the demand for data's storage density and capacity exerts explosive growth. However, traditional optical storage is hard to get rid of the bottleneck of optical diffraction limit. The persistent luminescence materials could be used for optical data storage based on the photon trapping and de‐trapping mode. Herein the performance of thermoluminescence (TL), photo‐stimulated luminescence, and photoluminescence of Pr³⁺‐doped Ca₄Ti₃O₁₀ were studied in order to explore the optical storage property of this material. The TL glow curves show that the deep‐trap in Ca₄Ti₃O₁₀:0.01Pr³⁺, Y³⁺ has a narrow distribution from 0.9 to 0.98 eV, which is qualified for maintaining the recorded data at RT for a long duration time. NIR photo‐stimulated red persistent luminescence (NIR‐to‐red mode) as presented in the Y‐containing Ca₄Ti₃O₁₀:Pr³⁺ phosphor could be a promising technique for optical data storage.     

Site occupancy and enhanced luminescence of broadband NIR gallogermanate phosphors by energy transfer

Super broadband near-infrared (NIR) La₃Ga₅GeO₁₄(LGGO): Cr³⁺ phosphor is in urgent needs for food testing. Unfortunately, it suffers from poor luminescence intensity in applications. Herein, the enhanced NIR luminescence performance can be realized in LGGO: Pr³⁺, Cr³⁺. The preferential crystallographic site of Cr³⁺ is validated on the basis of EPR spectrum, Rietveld refinement, and the first-principles DFT calculations. It is of great importance that the as-prepared phosphors can be excited by blue light (460 nm), which is beneficial to the application of blue-pumped LEDs. The critical distance of Pr³⁺ in LGGO host has been calculated by concentration-quenching method. For co-doped sample, it is observed that Cr³⁺ luminescence intensity enhancement by a factor of 3 can be achieved by doping Pr³⁺ owing to the energy transfer from Pr³⁺ to Cr³⁺. In addition, the introduction of Pr³⁺ can also improve the Cr³⁺ luminescence intensity at elevated temperature. Furthermore, using the optimized phosphor, a blue-based NIR phosphor-converted LEDs (NIR pc- LEDs) is fabricated, the forward voltage and the intensity of LED hardly change after thermal aging for 500 hours under high temperature/ high humidity condition, indicating its great reliability for NIR pc-LEDs. Therefore, LGGO:Pr³⁺, Cr³⁺ has great potential to serve as an attractive candidate in the application of blue light-excited NIR pc-LEDs in view of its capability for blue to enhanced broadband NIR conversion.     

Structure and Luminescence Characteristics of Eu3+‐Activated Trigonal Layered Perovskite Ba2La2ZnW2O12

Eu³⁺‐doped tungstate Ba₂La₂ZnW₂O₁₂ phosphors with perovskite‐structure were prepared by the high temperature solid‐state reaction. The X‐ray powder diffraction (XRD) patterns and structure refinements indicate that the phosphors crystalized in the trigonal layer‐perovskite. The luminescence properties of the phosphors were investigated such as photoluminescence (PL) excitation and emission spectra, decay lifetimes, and color coordinates. It was found that the pure host shows self‐activated emission excited by the UV light. Moreover, Ba₂La₂ZnW₂O₁₂ also shows scintillation characteristics under the X‐ray irradiation. The near‐UV and blue light can efficiently excite Eu³⁺‐doped Ba₂La₂ZnW₂O₁₂ phosphors inducing the strong orange–red luminescence. The optimal Eu³⁺ doping concentration in this host is 40 mol%. The luminescence spectra and the luminescence color of the phosphors strongly depend on the doping levels and excitation wavelength. The different luminescence features were discussed on the base of crystal structure. Eu³⁺ ions have two possible substitutions on A or B sites in this trigonal layered perovskite. The phosphor could act as a candidate for the potential application in near‐UV excited white‐LEDs lighting.     

Tunable ultra-wideband NIR emission and irradiation resistance in novel Er3+/Tm3+/Pr3+ tri-doped La2O3- Ga2O3-Ta2O5 glasses synthesized using aerodynamic levitation method

Glasses with ultra-wideband near-infrared emission and superior irradiation resistance are important for the potential applications in optical communications under harsh environments. Here, transparent 35La₂O₃-(65-x)Ga₂O₃-xTa₂O₅ (LGT) and Er³⁺/Tm³⁺/Pr³⁺ tri-doped LGT glasses are fabricated using the levitation method. LGT glasses exhibit a wide glass-formation region, low largest vibration energy, high refractive indices, and excellent mechanical properties. Additionally, Er³⁺/Tm³⁺/Pr³⁺ tri-doped LGT samples with varying Pr³⁺ contents are characterized by possessing good thermal stability (T_g>849°C), wide transparent optical window, strong radiation resistance, excellent compatibility between low wavelength dispersion (v_d>31.2), and large refractive index (n_d>2.048). By optimizing the doping content of Er³⁺, Tm³⁺, and Pr³⁺ in an appropriate ratio, the ultra-wideband near-infrared luminescence ranging from 1250 to 1640 nm (FWHM = 251 nm) has been acquired under 808 nm pumping. Furthermore, decay curves are measured to reveal the fluorescence dynamics, and then the related emission mechanism is elaborated systematically. Meanwhile, the effects of gamma irradiation doses on microstructure, transmittance spectra, and fluorescence characteristics are studied. This work may offer a valuable reference for doping optimization and new design strategy of multifunctional materials.     

A New Blue‐Emitting Phosphor of Ce3+‐Activated Fluorosilicate Apatite Ba2Y3[SiO4]3F

Blue‐emitting phosphor of Ce³⁺‐activated fluorosilicate apatite Ba₂Y₃[SiO₄]₃F was prepared via conventional solid‐state reaction method. The X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) excitation and emission spectra, and the decay curves (lifetimes) were applied to characterize the phosphors. The effects of Ce³⁺ activator concentration on the luminescence properties were investigated. Ba₂Y_2.85Ce_0.15[SiO₄]₃F exhibits the brightest blue emission with CIE coordinates of (x = 0.231, y = 0.301). The crystallographic site of Ce³⁺ ions in Ba₂Y₃[SiO₄]₃F lattices was identified. Two kinds of crystallographic Ce³⁺ occupying MI and MII sites in Ba₂Y₃[SiO₄]₃F lattices result in two distinct emission centers. The internal PL quantum efficiency, the temperature‐dependent luminescence, and the activation energy of thermal quenching were investigated to evaluate the potential application. This is a new kind of blue‐emitting phosphor based on apatite structure.     

Luminescent thermometry based on Ba4Y3F17:Pr3+ and Ba4Y3F17:Pr3+,Yb3+ nanoparticles

New effective luminescence thermometers based on novel host Ba₄Y₃F₁₇ doped with Pr³⁺ and Pr³⁺/Yb³⁺ in 80–320 K temperature range were studied. The absolute temperature sensitivity (S_a) of both Ba₄Y₃F₁₇: Pr³⁺(0.1 mol %) and Ba₄Y₃F₁₇: Pr³⁺(0.1 mol.%): Yb³⁺(10.0 mol.%)nanothermometers based on luminescence intensity ratio (LIR) between two Pr³⁺ emission bands (³P₁-³H₅ and ³P₀-³H₅) demonstrate a notable value (0.011 K⁻¹ at 300 K) in the 200–320 K range. The Ba₄Y₃F₁₇: Pr³⁺(0.1 mol.%): Yb³⁺(10.0 mol.%)nanothermometers based on LIR between ³P₀→³H₄ of Pr³⁺ and ²F_5/2→ ²F_7/2 of Yb³⁺ emission bands demonstrate high S_a into the 80–200 K range with maximal S_a = 0,0778 K⁻¹ at 100 K. The stability of the phosphors was revealed by thermo-cycling experiments.     

A multicolor persistent luminescent phosphor Sr2Ga2GeO7:Pr3+ for dynamic anticounterfeiting

Persistent luminescence (PersL) phosphor is a glow-in-the-dark material that has been widely applied. Here, we report a multicolor PersL phosphor Sr₂Ga₂GeO₇:Pr³⁺. The PersL color can be tuned from deep red to blue. It reveals that the luminescent color modulation of the Sr₂Ga₂GeO₇:Pr³⁺ phosphor is essentially associated with the cross-relaxation effect of Pr³⁺ in the host with low-phonon assistance energy. The PersL lifetime of the multicolor phosphors can be also tuned. Based on the unique features of Sr₂Ga₂GeO₇:Pr³⁺ phosphor, some simple PersL images are fabricated to emit dynamic multicolor information, and it shows that the PersL image even depicts dynamic multicolor anticounterfeiting.     

Li2SrSiO4:Ce3+, Pr3+ Phosphor with Blue,Red, and Near‐Infrared Emissions Used for Plant Growth LED

Ce³⁺/Pr³⁺ codoped Li₂SrSiO₄ (LSS) phosphors with blue, red, and near‐infrared (NIR) tri‐emission have been prepared via a high‐temperature solid‐state reaction method. Under the excitation of 200 to 400 nm near‐ultraviolet (n‐UV), the photoluminescence (PL) spectra of phosphors are composed of visible and NIR two parts. The former exhibits blue and red emission bands centered at around 428 nm from 5d–4f transition of Ce³⁺ and 611 nm from ¹D₂ → ³H₄ transition of Pr³⁺, those overlap with photosynthesis action spectra of plants and absorption spectra of chlorophylls and carotenoids. While the later presents a broad NIR emission band peaking near 1039 nm caused by the ¹G₄ → ³H₄ of Pr³⁺, matching with the absorption of bacteriochlorophyll. Their emission intensity ratios (B: R: NIR) could be tuned by altering the relative ratios of Ce³⁺ and Pr³⁺ concentration in the phosphors to meet the requirements of multifarious plants and bacteria. The efficient energy transfer from Ce³⁺ to Pr³⁺ takes place in the LSS host, which ascribed to an exchange interaction according to PL spectra and decay curves of phosphors. Results suggest that the present LSS: Ce³⁺, Pr³⁺ phosphors have great potential applications in plant growth n‐UV LED.     

Structural and spectroscopic analysis of green glowing down-converted BYO:Er3+ nanophosphors for pc-WLEDs

An energy efficient solution combustion technique was selected for fabricating a series of energy-efficient novel down-converted Ba₃Y₄O₉:Er³⁺ nanoparticles with green emission. Crystal structure engineering along with the morphological aspects was investigated via certain advanced characterizations such as Rietveld refinement and powder X-ray diffractometry (PXRD) procedure, microscopic practices like scanning and transmission electron microscope techniques, photoluminescence and diffuse reflectance spectroscopic analysis. Average crystallite size (65.71 nm–74.15 nm) and micro strain (0.0012) of the optimum powder nanomaterial were analyzed from high quality XRD data using Williamson-Hall (W–H) plot method. Alluring spectroscopic features were realized by photoluminescent (PL) spectra recorded upon excitation via near ultraviolet (NUV) source of 381 nm; displaying an intense emission peak (562 nm) situated in the visible region that is solely responsible for the green glow of the prepared phosphor. PL analysis witnessed a bright green emission via a reliable emanation transition (⁴S_3/2 → ⁴I_15/2) of Er³⁺ ions. Excellent colorimetric parameters of optimized nanophosphor like CIE coordinates (0.3420, 0.6064), 5356K CCT and 79.02% color purity validated its advanced photonic and optoelectronic applications for cool light emitting WLEDs, lasers, optical sensors, solar and photovoltaic cells.     

Trap distribution and photo-stimulated luminescence in LaSrAl3O7:Eu2+ long-lasting phosphors for optical data storage

Here, a green emission persistent luminescent phosphor LaSrAl₃O₇:Eu²⁺ which is chargeable by UV light, was synthesized by solid-state reaction method. Elemental mapping and fluorescence microscopy photoluminescence of the sample demonstrated the homogeneous distribution of La, Sr, Al, O, and Eu in the phosphor. Rietveld refinement shows that the as-prepared sample belongs to the tetragonal crystalline structure with space group of P42₁m. The Eu²⁺:5d-4f broad persistent luminescence with maximum emission peaking at 518 nm can be effectively obtained after irradiating in the UV light. A series of excitation temperature-dependent thermoluminescence measurements were conducted to gain some insight into the information of traps. Additionally, to verify its feasibility of optical data storage, specific information letters were encoded on the LaSrAl₃O₇:Eu²⁺ phosphor films using the laser of 405 nm, then the stored information could indeed be read out by thermal stimulation as expected. Meanwhile, NIR photo-stimulated red persistent luminescence was also obtained, which holds great potential for optical information storage. Finally, combined with the experimental and density functional theory calculation results, we proposed a tentative schematic diagram to account for the PersL and photo-stimulated persistent luminescence mechanism in LaSrAl₃O₇:Eu²⁺ phosphor.     

Spectroscopic Studies of Nanopowder and Nanoceramics La2Hf2O7:Pr Scintillator

Sintered nanoceramics of Pr‐doped lanthanum hafnate, La₂Hf₂O₇:Pr, were prepared by means of a high‐pressure sintering technique using nanopowders made by Pechini method. Structure, morphology, and spectroscopic properties of the ceramics compared to the starting powder are presented and discussed. Emission and excitation spectra recorded at room temperature as well as at 7 K using synchrotron radiation are presented together with results of luminescence kinetics measurements. In ceramics, at 7 K, the Pr³⁺ luminescence from ³P₀ (blue‐green, green, and red region) and ¹D₂ (red) levels is accompanied by a broad‐band emission located in the 380–530 nm range of wavelengths, whereas powders gives only the Pr³⁺‐related luminescence. Depending on the excitation wavelength, the broad‐band emission maximum moves between 430 and 470 nm indicating superposition of at least two components. In sintered nanoceramics, the lifetimes of Pr³⁺ emissions from ³P₀ and ¹D₂ levels were by 10%–20% shorter compared to the powder. The existence of different luminescence centers was proved by the selective emission decays examination. The fast 5d → 4f luminescence of Pr³⁺ was not observed from either of the two types of La₂Hf₂O₇:Pr materials.     

Developing "smart windows" for optical storage and temperature sensing based on KNN transparent ceramics

Smart windows have attracted considerable attention due to their wide applications in optical data storage, switchable sunroof and temperature sensing. The development strategy for smart windows is focused on performance design, enhancement and integration. However, developing integrated multi-functional smart windows in a single material remains a challenge. In this work, we have successfully prepared (K_0.5Na_0.5)_0.95Ba_0.04Er_0.01NbO₃ (4Ba-1Er-KNN) transparent ceramics for potential applications of temperature detection and optical information storage in smart windows. With alternating ultraviolet (UV) illumination and 300 °C thermal stimulation, the prepared 4Ba-1Er-KNN ceramics can not only achieve non-destructive luminescence readout, but also exhibits an ultra-high photochromic (PC) contrast with rapid response time of 1 s. Furthermore, based on the up-conversion (UC) photoluminescence (PL) intensity ratio of Er³⁺: ²H_11/2/⁴S_3/2 thermally coupled levels, excellent low-temperature sensing performance with the maximum relative sensitivity of 0.023 K⁻¹ at 213 K is obtained. The integration between UC PL, PC response and temperature sensing performance makes it possible to develop multi-functional smart windows.     

Self-activated persistent luminescence from Ba2Zr2Si3O12 for information storage

Till now, many doped persistent luminescence (PersL) phosphors have been investigated and found various applications in such as bioimaging, photocatalysis and information storage, but introducing PersL emitters into a proper host is mostly complex. In this research, a self-activated PersL phosphor Ba₂Zr₂Si₃O₁₂ (BZSO) is prepared by solid state reaction. By adding NH₄Cl, the self-activated PersL intensity is evidently enhanced. The trap depths and concentrations are examined by thermoluminescence spectra. Meanwhile, Bi³⁺ ions are introduced into BZSO and show wide band photoluminescence (PL) from 300 to 600 nm. Moreover, the PL of Bi³⁺ is tunable under excitation by 265-350 nm lights. Furthermore, as a proof-of-concept design, we designed a patterned quick response (QR) code based on the self-activated PersL of BZSO, and the information of “South China University of Technology (SCUT)” can be read out by the code scanning technology. Bi³⁺-doped BZSO phosphors are suggested to provide potential applications in information storage by its self-activated PersL, and to excite researchers to study the tunable PL in Bi³⁺-doped phosphor.     

Fatigue-resistant,temperature-insensitive strain behavior and strong red photoluminescence in Pr-modified 0.92(Bi0.5Na0.5)TiO3–0.08(Ba0.90Ca0.10)(Ti0.92Sn0.08)O3 lead-free ceramics

An electric-field-induced large strain and strong photoluminescence was achieved by introducing trivalent Pr³⁺ as the activator into 0.92(Bi_0.5Na_0.5)TiO₃ − 0.08(Ba_0.90Ca_0.10)(Ti_0.92Sn_0.08)O₃ (BNT−8BCST) ceramics. Around a critical composition of 0.4 mol% Pr³⁺, a large strain of ∼0.39% with a relatively small hysteresis compared with existing lead-free Bi-perovskite ceramics was obtained. In particular, the strain is very resistant to field cycling and thermal shock, giving the materials attractive for its exceptionally good fatigue resistance and high temperature stability. Besides the excellent electrical properties, Pr³⁺-modified BNT−8BCST host exhibits a strong photoluminescence with a bright red emission at 610 nm assigned to ¹D₂ → ³H₄ transitions of the Pr³⁺ ions upon a blue light excitation of 400–500 nm. The photoluminescence can be enhanced through poling treatment of the samples. Moreover, samples have a superior water resistance property which almost maintaining the same photoluminescence intensity after 40 h water immersion time. These results suggest the material may have potential application as a multifunctional device such as “on-off” actuator and electric field-controlled photoluminescence devices by integrating its excellent luminescence and electrical properties.     

Reversible and color controllable emissions in Er3+/Pr3+-codoped K0.5Na0.5NbO3 ceramics with splendid photochromic properties for anti-counterfeiting applications

It is highly significant to develop multi-mode optical anti-counterfeiting materials to efficiently fight against counterfeit products. In this study, we chose ferroelectric K_0.5Na_0.5NbO₃ (KNN) with excellent photochromism properties as the host and rare-earth Er³⁺ and Pr³⁺ ions as dopants to prepare the Er³⁺/Pr³⁺-codoped KNN ceramics. The color-tunable emissions can be obtained from red-orange-yellow to green by controlling the excitation wavelength. Upon 980 nm excitation, the synthesized ceramics does not only have superior upconversion (UC) emission behaviors but also have good luminescence modulation properties based on the photochromism properties. It is found that the KNN:0.003Er³⁺/0.003Pr³⁺ sample with the optimal UC emission features shows a highest ΔR_t value of 74.52% when irradiated by 390 nm light for 5 min, whereas the KNN:0.005Er³⁺/0.003Pr³⁺ ceramics also exhibit a high ΔR_t value of 66.81% under 395 nm light irradiation. According to the XPS and EPR results, one knows that the mechanism of luminescence modulation is closely related to defects and traps caused by the oxygen vacancies. Furthermore, the optical information writing and erasing test is conducted, exhibiting a good reproducibility and fatigue resistance. These results reveal that the designed ceramics are appropriate for the anti-counterfeiting applications.