Self-activated Luminescence Research Articles

Rare-earth-free Sr(Ca)2Ga2GeO7 phosphors with Ca-substitution-induced red-shift emission, perfectly aligned for Chlorophyll's absorption

Rare-earth-free Sr(Ca)2Ga2GeO7 phosphors exhibiting self-activated luminescence properties were synthesized by solid-state method. The incorporation of Ca in place of Sr resulted in a pronounced redshift in the emission spectrum, enabling a closer alignment with the absorption spectrum of chlorophyll. This advancement offers increased flexibility in designing blue LEDs optimized for diverse crop growth applications.

Intrinsic and defect-induced luminescence of lithium antimonate LiSbO3

Studies of investigating intrinsic and defect-induced luminescence in semiconductors can yield valuable insights into the underlying mechanisms and their significance for optoelectronic applications. This research focuses on self-activated lithium antimonate LiSbO3, synthesized through a solid-state reaction method. The as-prepared samples underwent post-annealing treatment in air and a CO atmosphere, respectively. The work investigated the phase formation, structures, elemental composition, band transition characteristics, luminescence properties, and decay lifetimes of the self-activated phosphors. LiSbO3 is identified as an n-type semiconductor with a direct allowed transition and the band gap energy of 2.97 eV. The experiment also confirmed the presence of oxygen vacancy (VO) centers during the synthesis of LiSbO3. The self-activated luminescence of LiSbO3 was found to be sensitive to the post-annealing atmosphere. Notably, post-annealing in a reducing environment significantly enhances the luminescence efficiency. The luminescence characteristics and thermal stability of LiSbO3 are closely linked to oxygen defects, which play a critical role in the color emissions of this self-activated phosphor.

Nonstoichiometry-Induced Self-Activated Phosphors for Dynamic Anti-counterfeiting Applications.

Optical signals with distinctive properties, such as contactless, fast response, and high identification, are harnessed to realize advanced anti-counterfeiting. However, the simultaneous attainment of multi-color, -temporal, and -modal luminescence performance remains a compelling and imperative pursuit. In our work, a temperature/photon-responded dynamic self-activated luminescence originating from nonstoichiometric Zn2GeO4 is developed with the modulation of intrinsic defects. The increased concentration of oxygen vacancies (VO••) contributes to an enhanced recombination of ZnGe″-VO••, ultimately improving the self-activated luminescence performance. Additionally, the photoluminescence (PL) color of the representative Zn2.2GeO4 sample changes from green to blue-white with the increased ultraviolet (UV) irradiation time. Concurrently, the emission color undergoes a variation from blue to green as the ambient temperature raises from 280 to 420 K. Remarkably, green long persistent luminescence (LPL) and photostimulated luminescence (PSL) behaviors are observed. Herein, this study elucidates a sophisticated anti-counterfeiting approach grounded in the dynamic luminescent attributes of nonstoichiometric Zn2GeO4, presenting a promising frontier for the evolution of anti-counterfeiting technologies.

Double-perovskite compound Na2ZrTeO6: Synthesis, structure and self-activated near-infrared luminescence

Perovskite compounds are always the focus in the material research field. Herein, the polycrystalline samples and single crystals of Na2ZrTeO6, a B-site ordered double-perovskite compound, were prepared successfully. Single crystal X-ray diffraction demonstrated that Na2ZrTeO6 crystallizes in the cubic space group Fm-3m (No. 225) with unit parameters of a = b = c = 7.80360(10) Å. The crystal structure of Na2ZrTeO6, formed by ZrO6 and TeO6 octahedra through sharing the corner oxygen atoms, belongs to the typical rock-salt-type perovskite structure. The density functional theory calculations show that Na2ZrTeO6 has a direct band gap with band gap of 3.21 eV, which is lower than the experimental value of 3.85 eV. Interestingly, the powder samples of Na2ZrTeO6 exhibit a self-activated near-infrared emission centered at 780 nm under ultraviolet light excitation. And a strong luminescence thermal stability was also observed. Compared to room temperature, the luminescence intensity can maintain 64 % at 200 °C.

Tailoring the structure and self-activated photoluminescence of carbonated amorphous calcium phosphate nanoparticles for bioimaging applications.

Self-activated luminescent calcium phosphate (CaP) nanoparticles, including hydroxyapatite (HA) and amorphous calcium phosphate (ACP), are promising for bioimaging and theragnostic applications in nanomedicine, eliminating the need for activator ions or fluorophores. In this study, we developed luminescent and stable citrate-functionalized carbonated ACP nanoparticles for bioimaging purposes. Our findings revealed that both the CO32- content and the posterior heating step at 400 °C significantly influenced the composition and the structural ordering of the chemically precipitated ACP nanoparticles, impacting the intensity, broadness, and position of the defect-related photoluminescence (PL) emission band. The heat-treated samples also exhibited excitation-dependent PL under excitation wavelengths typically used in bioimaging (λexc = 405, 488, 561, and 640 nm). Citrate functionalization improved the PL intensity of the nanoparticles by inhibiting non-radiative deactivation mechanisms in solution. Additionally, it resulted in an increased colloidal stability and reduced aggregation, high stability of the metastable amorphous phase and the PL emission for at least 96 h in water and supplemented culture medium. MTT assay of HepaRG cells, incubated for 24 and 48 h with the nanoparticles in concentrations ranging from 10 to 320 μg mL-1, evidenced their high biocompatibility. Internalization studies using the nanoparticles self-activated luminescence showed that cellular uptake of the nanoparticles is both time (4-24 h) and concentration (160-320 μg mL-1) dependent. Experiments using confocal laser scanning microscopy allowed the successful imaging of the nanoparticles inside cells via their intrinsic PL after 4 h of incubation. Our results highlight the potential use of citrate-functionalized carbonated ACP nanoparticles for use in internalization assays and bioimaging procedures.

Multifaceted insight into the cation-disordered self-activated luminescence of Zn3V2O8 compositions for lighting and pigment applications

Remarkable structural diversity-dependent photoluminescence and UV-vis absorption have been induced in Zn3V2O8 through several cationic substitutions (In3+, Y3+, Bi3+, and K+), which ensured potential lighting and pigment applications.

A Novel Self-activated Near-infrared Luminescence of BaLaMgTaO6 Phosphor

BaLaMgTaO6 is an excellent phosphor host with very interesting properties. In this research, we have synthesized a new near-infrared emitting BaLaMgTaO6 phosphor. Upon ultraviolet-light excitation (365 nm), the BaLaMgTaO6 host displays a broad emission ranging from 650 to 750 nm. The as-prepared samples were characterized and analyzed with temperature-dependent and time-resolved photoluminescence (PL), as well as X-ray photoelectron spectroscopy (XPS). Through the experimental design, we determined that the luminescence observed in the BaLaMgTaO6 compound can be attributed to the presence of multiple defects. These findings suggest that this material could serve as a promising platform for modeling new near-infrared phosphors and be utilized in the field of solid-state lighting.

Broadband emission characteristics and WLED application of self-activated YMZn3AlO7 (M=Ca, Sr, Ba) phosphors

In this study, a non-activated ion-doped full-spectrum emission phosphor for white light-emitting diode (WLED) lighting is proposed using oxygen defect engineering. The YMZn3AlO7 (M = Ca, Sr, Ba) phosphors with "114″ structure were prepared via a high-temperature solid-state reaction. Under excitation with 373 nm ultraviolet (UV) light, YSrZn3AlO7 in YMZn3AlO7 (M = Ca, Sr, Ba) exhibited the highest emission intensity and formed a wide yellow emission band centred at 563 nm. The full width at half maximum of the YSrZn3AlO7 phosphor was 172.6 nm. A theoretical model based on the designed oxygen vacancies was proposed to determine the self-activated luminescence mechanism. Density functional theory calculations revealed that oxygen vacancies lead to the generation of new energy levels. Electron paramagnetic resonance experiments further confirmed that the luminescence originated from oxygen vacancies. Eventually, a warm WLED device ((x, y) = (0.4057, 0.4359)) with a correlated color temperature of 3814 K and a relative color rendering index of 83 was successfully prepared using the YSrZn3AlO7 phosphor and a 365 nm UV LED chip. These results suggest that YSrZn3AlO7 is a promising WLED phosphor and provide new insights into the application of self-activated phosphors in WLED.

Nd3+ emission in the garnet structure of LiCa3ZnV3O12 phosphor

Nd3+ doped vanadate phosphors are well known, mainly for their suitability for solid-state laser applications. Garnet structures are also explored for such purposes. LiCa3ZnV3O12 is one of them. Luminescence in this host has not yet been investigated. The luminescence characteristics of LiCa3ZnV3O12:Nd3+ are reported here. Two types of emissions have been observed. The self-activated luminescence could be observed under UV excitation. The characteristic emission of Nd3+ is also observed. Apart from the f–f excitation, an efficient host sensitization of Nd3+ luminescence is observed. The LiCa3ZnV3O12:Nd3+ phosphor showed an intense Near Infrared emission at 1068 nm due to the transition of 4F3/2 → 4I9/2, for 350 nm excitation.

Intrinsic- and Rare Earth Ion-Activated Luminescence in NbAlO4 with Wide Structure Channels.

Compounds with ordered and interconnected channels have versatile multifunctional applications in technological fields. In this work, we report the intrinsic- and Eu3+-activated luminescence in NbAlO4 with a wide channel structure. NbAlO4 is an n-type semiconductor with an indirect allowed transition and a band-gap energy of 3.26 eV. The conduction band and valence band are composed of Nb 3d and O 2p states, respectively. Unlike the common niobate oxide Nb2O5, NbAlO4 exhibits efficient self-activated luminescence with good thermal stability even at room temperature. The AlO4 tetrahedron effectively blocks the transfer/dispersion of excitation energy between NbO6 chains in NbAlO4, allowing for effective self-activated luminescence from NbO6 activation centers. Moreover, Eu3+-doped NbAlO4 displayed a bright red luminescence of 5D0 → 7F2 transition at 610 nm. The site-selective excitation and luminescence of Eu3+ ions in a spectroscopic probe were utilized to investigate the doping mechanism. It is evidenced that Eu3+ is doped in the structure channel in NbAlO4 lattices, not in the normal cation sites of Nb5+ or Al3+. The experimental findings are valuable in developing new luminescent materials and improving the understanding of the material's channel structure.

Synthesis and characterization of luminescent Cu2+-doped fluorapatite nanocrystals as potential broad-spectrum antimicrobial agents.

Nanomaterials based on metal-doped fluorapatite (FAP) have attracted considerable interest as potential next-generation antimicrobial agents. In this study, Cu2+-doped FAP nanocrystals have been successfully synthesized by a neutralization method at room temperature. Their structural, optical, antimicrobial, and hemcompatible properties have been investigated. XRD, FTIR, FESEM, and N2 adsorption-desorption studies indicate the formation of single-phase FAP mesoporous nanopowders, composed of rod-like particles. TEM images confirmed the formation of nanorodes with a length of 60nm and a width of about 18nm. Rietveld analysis shows that the Cu2+ ions preferentially substitute Ca2 (6h) sites in the hexagonal fluorapatite crystal structure. Fluorescence spectroscopy accompanied by MCR-ALS method confirms substitution of Cu2+ ions in FAP crystal lattice with extracting additional d-d band transition at green color from FAP broadband self-activated luminescence in violet-blue color. Antimicrobial studies conducted on Staphylococcus aureus, Escherichia coli and Micrococcus lysodeikticus showed that FAP nanopowder with the highest Cu2+ content have strong bacteriostatic action on Staphylococcus aureus bacterial strain in mediums containing nutrition matters. In addition, this sample in comparison to pure FAP achieved a high percentage of relative reduction of bacterial population for all three species, being >90% in most cases. Fungistatic action is noticed too, throwgh the slowing down mycelium growth of fungus Aspergillus niger, Aspergillus flavus and Penicillium roqueforti and reduction of sporulation of Aspergillus niger species. Cu2+-doped FAP nanocrystals shows a synergistic antimicrobial effect with Cu2+ and F- ions. Concerning the potential biomedical applications, the hemolysis ratios of the Cu2+-doped FAP samples were below 5%. The obtained results pointed out the possible use of the synthesized nanocrystals as broad-spectrum antimicrobial agents for various biomedical and health care preparations.

Self-activated rare-earth free phosphor prepared by propylene glycol-modified silane

A facile wet-chemistry method can be applied to produce efficient rare-earth-free LED phosphors. In this study, self-activated Ca2SiO4 phosphor was developed using a propylene glycol-modified silane (PGMS) as a silicate source. The structural and luminescence properties of samples were characterized using synchrotron X-ray powder diffraction and photoluminescence (PL) spectroscopy, respectively. The PGMS phosphor consists of mixed crystal phases of α′L, β, and γ, whereas the solid-state reaction (SSR) phosphor only has a β phase. The synthesized PGMS phosphor with distinctive crystal defects shows self-activated luminescence, while the SSR phosphor has no PL properties.

Improvement of self-activated luminescence properties of Ca2KZn2(VO4)3 down-conversion materials by SSR method based on co-doped Eu3+,Dy3+ rare earth ions concentrations

In this study, a self-activated and co-doped Eu, Dy with Ca2KZn2(VO4)3 (CKZVO) phosphors were synthesized by conventional solid state reaction method. The powder X-Ray diffraction study confirm the formation of single phase cubic crystal structure with space group Ia3̅d. The surface morphology of as-synthesized phosphor was verified by SEM analysis. The FTIR spectrum shows characteristic bonds, for bending vibration and asymmetric stretching vibration. In photoluminescence under the UV excitations the CKZVO phosphor display greenish blue emission due to the VO4 transitions ions in host matrix. The PL characteristic of CKZVO: Dy3+ phosphors exhibits intense emission centred at 480 nm (blue) and 573 nm (yellow color). Moreover, CKZVO: Eu3+ phosphor exhibits strong emission at 500 nm (green) and 615 nm (Red) under UV excitation. Further co-doping of Dy3+, Eu3+ in the host matrix reveals a strong emission in blue, green, yellow and red region. The chromaticity coordinates of the samples were in near white region. All the results exhibit that CKZVO: Dy3+, Eu3+ phosphor might be a potential material for NUV-based white light-emitting diodes.

Amorphous calcium phosphate nanoparticles allow fingerprint detection via self-activated luminescence

Herein, stable activator-free photoluminescent nanoparticles based on amorphous calcium phosphate (ACP) were obtained for the first time, and their performance for latent fingerprint imaging was investigated. ACP nanoparticles with irregular rounded shape and diameters in 10–40 nm range were prepared by a rapid and simple chemical precipitation followed by heat treatment at 400 °C for 4 h. Notably, diffuse reflectance spectroscopy, photoluminescence excitation and emission measurements reveal a high density of localized energy states within the wide optical band gap of heat-treated ACP (Eg = 5.25–5.42 eV). This behavior allowed the excitation of ACP in near-ultraviolet region (λexc = 450 nm, 2.75 eV), leading to an intense defect-related broadband (490–890 nm) photoluminescence emission centered at 540 nm (2.30 eV), 50 times more intense than untreated nanoparticles. The effect of lattice shrinkage due to structural water elimination, the presence of ionic vacancies (VCa and VO in PO43-) and carbonate groups (CO32-), on the luminescent properties of ACP were discussed in detail, as well as investigated after aqueous-mediated ACP crystallization into hydroxyapatite (HA). ACP nanoparticles were non-cytotoxic, as determined by MTT assay in Human Dermal Fibroblast neonatal (HDFn) cell line, with cell viabilities superior to 95% in all tested concentrations (20–320 μg/mL), after incubation for 24 and 48 h. Latent fingerprint images were obtained using the ACP nanoparticles under near-ultraviolet irradiation (λexc = 450 nm) in tweezers and LCD smartphone and successfully validated by the Integrated Automated Fingerprint Identification System used by Scientific Police in Spain. The present results evidenced that the new luminescent ACP nanoparticles are safe to be used and agree with the forensic requirements for future legal actions.

A novel self-activated ultraviolet persistent luminescence material and its anti-counterfeiting application based on intensity and time resolution from persistent luminescence

Recently, the ultraviolet (UV) persistent luminescence material (PLM) has attracted extensive attention. However, the design and development of new UV PLM and exploring their promising advanced application remain challenges. Here, we developed a new dopant-free self-activated UVA PLM, Zn2Al2SiO7, which could be applied in anti-counterfeiting field. Zn2Al2SiO7 shows UVA persistent luminescence (PersL) peaking at 380 nm after 254 nm UV lamp excitation. Addition of Yb3+, the UVA PersL intensity and time are raised obviously, and the UVA PersL time lasts more than 24 h. In addition, Yb3+-doped Zn2Al2SiO7 exhibits photostimulated properties with different light source. Finally, we design anti-counterfeiting pattern based on intensity and time resolution from PersL of Zn2Al2SiO7, showing its advantages in the anti-counterfeiting field.

Improvement of Self-Activated Luminescence Properties of Ca2kzn2(Vo4)3 Down-Conversion Materials by Ssr Method Based on Co-Doped Eu3+,Dy3+ Rare Earth Ions Concentrations

Improvement of Self-Activated Luminescence Properties of Ca2kzn2(Vo4)3 Down-Conversion Materials by Ssr Method Based on Co-Doped Eu3+,Dy3+ Rare Earth Ions Concentrations

The synergism between self-activated and impurity-related emissions of LiCa3ZnV3O12: lattice distortion, energy transfer and temperature sensing effect.

Some of the metal vanadates have special self-activated luminescence. In order to further enrich its luminous color, luminescent impurity ions can be introduced into its lattice. The interaction between the self-activated emission and the impurity-related emission remains to be studied. In this work, the synergism between the two kinds of emission in LiCa3ZnV3O12 was explored from these three aspects: lattice distortion, energy transfer and temperature effect. Eu3+ ions replace Ca2+ ions in the lattice of LiCa3ZnV3O12, leading to a lattice contraction of the LCZV host, which depresses the self-activating emission around 500 nm. The characteristic linear emissions of Eu3+ ions are also observed benefiting from the energy transfer from [VO4]3- to Eu3+. Since the temperature quenching effect is more sensitive for the self-activated emission than that for the Eu3+-related ones, the phosphor can be applied as a luminescent temperature sensor, with the absolute and relative temperature sensitivities of 0.012 K-1 and 1.56% K-1, respectively.

Synthesis and properties of Sm<sup>3+</sup> doped NaLa(WO<sub>4</sub>)<sub>2</sub> single matrix white phosphors

<sec>Single ion doped single phase white emitting phosphors have some special advantages and great potential applications in the field of high quality LED lighting. This type of phosphors can effectively solve the problem of uneven particle dispersion and sedimentation in the white light scheme obtained by UV chip plus trichromatic phosphor, and solve the problems of the luminescence and reabsorption between phosphors and the regulation of trichromatic ratio. A comparison of the single-ion doping luminescent material with the multi-ion doping system shows that the single-ion doping luminescent material is simpler in both preparation process and luminescence color adjustment, which can achieve higher color rendering index, more easily controlled color temperature and closer to the color coordinates of white light. </sec><sec>According to the principle of colorimetry and luminescence, light of two or more wavelengths may be combined to obtain white light emission. Under the UV excitation, the Sm<sup>3+</sup> ions emit relatively strong green, yellow, orange and red light at 580–670 nm. Under UV excitation, the broadband spectrum of <inline-formula><tex-math id="Z-20210831172528">\begin{document}${\rm{WO}}_{4}^{2-} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20210493_Z-20210831172528.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20210493_Z-20210831172528.png"/></alternatives></inline-formula> self-activated emission covers almost the whole visible region, but the blue-green light is strong in the short wavelength region and the yellow-orange-red light is weak in the long wavelength region. When Sm<sup>3+</sup> ions are doped into tungstate, Sm<sup>3+</sup> ions’ luminescence can effectively supplement the weak luminescence intensity of tungstate in the long-wave region, and white light can be obtained. Under the excitation of 250 nm, the phosphor emits cold white light, and warm white light under the excitation of 403 nm. The experimental results show that Sm<sup>3+</sup> ions have a significant effect on the correlated color temperature adjustment of self-activated luminescence of NLW phosphors. All the prepared samples are crystallized into the tetragonal crystal phase structures and that their morphologies present rhombic sheet. By analyzing the experimental data, the type of energy transfer between Sm<sup>3+</sup> ions is determined to be electrical dipole–electrical dipole interaction. The NLW: <i>x</i>Sm<sup>3+</sup> phosphor has high stability and can be effectively excited by ultraviolet/near-ultraviolet light, which can be used as a potential candidate of single matrix single-ion doped white phosphors.</sec>

KCa2Mg2V3O12: A novel efficient rare-earth-free self-activated yellow-emitting phosphor

The development of efficient near-ultraviolet (near-UV) excitable inorganic phosphors is highly important for application in near-UV-pumped white light-emitting diodes (LEDs). Herein, we reported on a novel efficient rare-earth-free yellow-emitting KCa2Mg2V3O12 vanadate phosphor. These phosphors were prepared by using a conventional high-temperature solid-state reaction method. Photoluminescence study revealed that KCa2Mg2V3O12 phosphor exhibited a broad excitation band in the 250−420 nm wavelength range with a peak at 346 nm, owing to the absorption of [VO4]3− groups. Upon 346 nm excitation, KCa2Mg2V3O12 phosphor showed bright yellow emission in the 400−800 nm range with a maximum at 540 nm and a full width at half maximum of 161 nm. Such self-activated broadband yellow luminescence was attributed to the 3T2→1A1 and 3T1→1A1 transitions of [VO4]3− groups. The Commission Internationale de l´Eclairage (CIE) color coordinates were calculated to be (0.3741, 0.4679), which were located in the yellow region in the CIE chromaticity diagram. Impressively, the internal quantum efficiency of KCa2Mg2V3O12 phosphor was measured to be as great as 41 %. In addition, the temperature-dependent emission spectra were recorded, and the activation energy Ea was determined to be 0.366 eV. The newly developed KCa2Mg2V3O12 phosphor might have application potential as color converter in white LEDs.

Strategy to modify intrinsic luminescence via post-annealing treatment and impurity doping in SbNb3(PO4)6

Self-activated luminescence of a phosphor has unique advantages such as natural homogeneity, wide wavelength, without rare-earth dopant, easy preparation, etc. However, its luminescence efficiency usually is not satisfied. This work reports several strategies to modify the intrinsic luminescence intensity of SbNb3(PO4)6 synthesized via the sol–gel method. XRD measurements were conducted to verify phase formations and structural characteristics. The transition natures and band energy were determined on the basis of the optical absorption. SbNb3(PO4)6 shows a broad self-activated luminescence (400–750 nm) peaked at 485 nm. Impurity ion V5+ doping improves the intrinsic luminescence of SbNb3(PO4)6. The optimal efficiency of 31.63% was observed in 7.0 mol% V5+-doped SbNb3(PO4)6. Post-annealing of as-prepared SbNb3(PO4)6 in the air can enhance the luminescence, while, annealing in CO atmosphere deteriorates the intensity. The luminescence thermal stabilities and activation energies were evaluated via the temperature-dependent emission intensities and decay lifetimes. The intrinsic defects such as oxygen vacancies (VO••) were confirmed via XPS measurements, which exerted great influences on the emission and thermal stabilities of the emission. The abnormal blue-shift of the emission spectra was presented from 10 to 350 K. The luminescence mechanism was proposed for the self-activated emission based on the dynamic emission spectra, decay time, and multiple color centers.