Preparation and characterization of new red luminescent fibers based on a multilayer structure

Abstract

Composite red luminescent material SMED/LCA (Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/light conversion agent) is a phosphor with long afterglow, which was prepared by LCA and SMED at a certain mass ratio. It has excellent characteristics, such as high lightness and emitting red light, but poor stability properties because LCA falls off easily from the surface of SMED. Here, SiO₂ (Al₂O₃ or MgF₂) was coated on the surface of SMED/LCA through the heterogeneous deposition method to prepare a stable composite phosphor, adding coated phosphor into a polyacrylonitrile (PAN) fiber-forming polymer and wet spinning to form SMED/LCA-PAN (composite red light-emitting fiber). The surface element distribution, phase structure and luminescence properties of SMED/LCA-PAN were characterized. The results show that SiO₂ (Al₂O₃ or MgF₂) is successfully coated on the surface of the material, and the coating has no effect on the phase of SMED in the fibers. The intensity red/blue ratio (Int.600 nm versus Int.470 nm) of coated SMED/LCA fiber in the afterglow emission spectrum increases by about 1.9 times; the increase in energy conversion efficiency indicates the enhancement of the red light effect. In addition, the afterglow initial brightness is up to 0.148 cd/m² after 15 min of ultraviolet light excitation, and the luminous fiber still has high afterglow brightness.

Keywords

luminescent fiber light conversion agent polyacrylonitrile

Fiber doped with rare-earth luminescent materials is a type of photoluminescent fiber, which has excellent characteristics of high luminescent efficiency, long afterglow, no harmful radiation, non-toxicity and chemical stability. These fibers can be luminous in the dark for more than 10 h after excited by ultraviolet (UV) or visible light for a few minutes.¹^–4 Because the emission color of most commercial rare-earth luminescent materials is mainly restricted from the blue to the green region, the afterglow color of the fibers is mainly green and blue. There are no excellent red-emitting persistent luminescent materials applied in fibers.⁵^–7 A major concern in luminescent fibers today is to expand the spectral range, as they are widely used in transportation, architectural decoration, toys, embroidery, warning signs, fabrics, etc.⁸,⁹ In recent years, warm color luminescent materials have been prepared through changing the substrate, selecting different rare-earth activators and adopting new methods. The results show that the fluorescence intensity was too weak to meet the requirements of fiber applications in most cases.¹⁰^–15

A color conversion concept is developed to expand persistent luminescence color, utilizing commercial phosphors as persistent luminescence donor phosphors, and a kind of red conversion material is used to tune the persistent luminescence spectra from blue or green to red.¹⁶^–20 Chen et al.²¹ regulated the weight ratio of CaAl₂O₄:Eu²⁺,Nd³⁺ and Y₃Al₅O₁₂:Ce³⁺ microparticles, and successfully generated long persistent luminescence color tuned linearly from blue to yellow. Zhang et al.²² grafted silica precursors to Sr₄A1₁₄O₂₅:Eu²⁺,Dy³⁺ via the silicon–oxygen bond, then a bonded light conversion agent (LCA) to SiO₂–Sr₄A1₁₄O₂₅:Eu²⁺,Dy³⁺ by a silane coupling agent. Zhu and Ge²³ reported a new luminous fiber that can emit red light at the wavelength of 600 nm by SrAl₂O₄:Eu²⁺,Dy³⁺/LCA. Chen et al.²⁴ introduced a multicolored polyamide 6 (PA6) luminous fiber with warm-toned luminescence prepared by a SrAl₂O₄:Eu²⁺,Dy³⁺/SiO₂-coated red-emitting coumarin color converter. Transferring the radiative energy from commercial phosphors to red conversion material, a composite phosphor with the red color of persistent luminescence was successfully obtained. However, phosphor and LCA are dispersed in the fiber substrate separately in the spinning process due to the unstable combination. The luminescent fiber prepared from the composite phosphor shows a weak conversion efficiency.

In order to improve the conversion efficiency of composite luminescent materials, and optimize the red light-emitting properties of luminescent fibers, a stable composite phosphor was prepared based on a multilayer structure. In this paper, Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ SMED and LCA were combined by an aluminate coupling agent to prepare composite red luminescent materials, which were coated by SiO₂, Al₂O₃ and MgF₂ individually through the heterogeneous deposition method to improve its stability in fibers,²⁵^–30 then the coated composite phosphors was added into a polyacrylonitrile (PAN) fiber-forming polymer and wet-spun to form SMED/LCA-PAN.³¹,³² The surface element distribution, phase structure and luminescence properties of the fibers were characterized by scanning electron microscopy (SEM), an X-ray diffractometer (XRD), a fluorescence spectrometer and an afterglow luminance meter, and the results were discussed.

Experimental details

Preparation of SMED/LCA-PAN fiber

We have previously described the method used to prepare the raw SMED and LCA.³³,³⁴ To prepare composite phosphor SMED/LCA and improve the conversion efficiency of SMED/LCA in the fiber substrate, SMED was utilized as a persistent luminescence donor phosphor, while the LCA was chosen to tune the persistent luminescence spectra from blue to red. SiO₂, Al₂O₃ and MgF₂ were used as coating materials to improve the stability of SMED/LCA. Coated SMED/LCA was prepared by the following method prior to wet spinning.

LCA, SMED and C₂H₆O were added into a beaker and stirred constantly for 30 min, then the aluminate coupling agent was added into compound above, stirring and heating in a water bath at 40–50°C for 30 min, followed by ultrasonic treatment for 15 min (frequency: 100 kHz). Then the samples were stirred and heated at 60–70°C until the alcohol was evaporated and then the samples were placed in the oven at 70°C for 2 h; the products were then milled and sieved to get the desired samples of SMED/LCA.

Na₂SiO₃ and deionized water were added into a beaker and stirred for 30 min, then SMED/LCA was added into the compound and stirred constantly for 1 h, while HNO₃ was dripped gradually to adjust the pH to 9. SiO₂-coated SMED/LCA samples were prepared after filtration and drying. NH₄F and deionized water were added into a beaker and stirred for 30 min, then SMED/LCA was added into the compound and stirred constantly for 1 h, while MgCl₂ was dripped gradually. MgF₂-coated SMED/LCA samples were prepared after filtration and drying. Al(NO₃)₃ and deionized water were added into a beaker and stirred for 30 min, then SMED/LCA was added into the compound and stirred constantly for 1 h, while HNO₃ was dripped gradually to adjust the pH to 5. Al₂O₃-coated SMED/LCA samples were prepared after filtration and drying.

PAN was used as the spinning substrate to prepare luminous fiber. PAN and dimethyl sulfoxide (DMSO) were accurately weighed by a mass ratio of 19:100. Then they were added into a beaker, stirring and heating constantly in a water bath at 60–70°C for 4 h to prepare the PAN fiber-forming polymer. The coated SMED/LCA samples were added into the PAN fiber-forming polymer and wet-spun to form SMED/LCA-PAN fiber. The ratio of doped composite luminescent materials to PAN fiber-forming polymer in the samples was 10:100. The coagulation bath was an aqueous solution.

Characterization

The microstructures of the samples were observed using SEM on a scanning electron microscope (Quanta200, the Netherlands), at an accelerating voltage of 5 kV. In order to investigate the distribution of SiO₂, Al₂O₃, MgF₂ and SMED/LCA in the luminescent fibers, the fibers were observed using SEM on a scanning electron microscope at an accelerating voltage of 20 kV. An energy-dispersive X-ray spectroscopy (EDS) instrument (7353, Oxford, UK) with 133 eV resolution was used for elemental analysis of the samples. All samples were dried and coated with gold before scanning. X-ray diffraction patterns were recorded on a D8 Advance XRD (Bruker AXS, Germany) with Cu Kα radiation (λ = 0.15406 nm) at a voltage of 40 kV and current of 30 mA. Samples were scanned over the range of diffraction angle 2θ = 5°–90°, with a scan speed of 0.2(°)/s at room temperature. The excitation and emission spectrum of all the samples were measured by a fluorescence spectrophotometer (HITACHI650-60, Japan) at room temperature with an Xe flash lamp as an excitation source; the scan speed was 120 nm/min. Chromaticity coordinates were tested and chromaticity diagrams were obtained by a fluorescence spectrophotometer. Afterglow decay curves were tested using a PR-305 afterglow brightness tester (excitation illumination: 1000 lx, excitation time: 15 min) at room temperature. Before testing, samples were placed in darkness for more than 15 h to ensure that the afterglow illumination had been attenuated completely. The digital pictures of all the samples were taken by using a SLR (single-lens reflex) camera with an Xe flash lamp as the excitation source.

Results and discussion

SEM analysis

Figure 1 shows the SEM images of the luminescent fibers. It can be seen from Figures 1(a) and (b) that the diameter of the fiber is about 120 µm, and irregularly shaped particles of SMED are clearly visible. Figure 1(c) shows a cross-section of fiber containing SMED/LCA. We can see many round LCA particles are distributed around SMED in the fiber. The LCA falls off the surface of SMED during the spinning process due to the bond fastness being too low. Figures 1(d)–(f) show cross-sections of coated SMED/LCA fibers. Compared with SMED/LCA fiber, LCA particles dispersed in the fiber become sparse and hardly visible in the Al₂O₃-coated SMED/LCA fiber. This indicates that the LCA is still attached to the surface of SMED, thus ensuring high efficiency light color conversion. Schematic diagrams of phosphor and its distribution in the fibers are shown in Figure 2, where the large blue particles are SMED and the small red particles are LCA. The red particles adhere to the surface of the blue particles through an aluminate coupling agent as an intermediate bridge. The large blue particles absorb sunlight and store it, then release blue light. The small red particles convert most of the blue light into red light to achieve the conversion of light color. The fiber in Figure 2(a) contains SMED, which has a blue afterglow. The fiber in Figure 2(b) contains SMED/LCA, and we can see that the red particles fall off from the blue particles and are dispersed in the fibers alone, resulting in low conversion efficiency of the LCA, so that the fiber in Figure 2(b) shows a poor red light effect. The fiber in Figure 2(c) contains coated SMED/LCA, where SiO₂, Al₂O₃ and MgF₂ are coated on the surface of SMED/LCA like a protective shell to maintain its stability in fibers; the LCA is well distributed on the surface to ensure a high conversion efficiency.

Figure 1.

Scanning electron micrographs of fibers containing different luminescent materials: (a) fiber containing Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ (SMED); (b) cross-section of fiber containing SMED; (c) SMED/light conversion agent (LCA); (d) SiO₂-coated SMED/LCA; (e) MgF₂-coated SMED/LCA; (f) Al₂O₃-coated SMED/LCA.

Figure 2.

Coating process for Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ (SMED) and its distribution in the fibers. LCA: light conversion agent. (Color online only.) (a) Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ (b) SMED/LCA and (c) coated SMED/LCA.

EDS analysis

To analyze the component of coated phosphor in the fiber, a random and repeated SEM-EDS scan was carried out on the fibers. Figures 3(a) and (b) show the EDS spectrum and the weight% of the elements of fibers containing SMED/LCA and SiO₂-coated SMED/LCA. As can be seen from Figure 3(a), a characteristic energy-dispersive peak of Si is observed at 1.8 eV, which belongs to the Si elements in SMED materials. The relative content of Si is about 25%. However, for the SiO₂-coated SMED/LCA fibers in Figure 3(b), the relative content of Si is about 44.74%. Obviously, the increase in the contents of Si is observed due to surficial SiO₂ coating of phosphor particles. Because the LCA on the surface of SMED falls off easily, the SiO₂ coating was used to improve the stability of the SMED/LCA in application. After the complicated spinning process, the still existing SiO₂ coating on the surface of SMED/LCA means that the coating can maintain the stability of the SMED/LCA in solution spinning. EDS spectra and the weight% of the elements for MgF₂-coated SMED/LCA and Al₂O₃-coated SMED/LCA are shown in Figures 3(c) and (d). The relative contents of F and Al distributing on the coated phosphors surface are about 24.17% and 14.47%, respectively, which provides evidence for the presence of MgF₂ and Al₂O₃ on the particle surfaces.

Figure 3.

Energy-dispersive X-ray spectroscopy (EDS) spectrum of fibers containing different luminescent materials: (a) EDS spectrum of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/light conversion agent (SMED/LCA); (b) EDS spectrum of SiO₂-coated SMED/LCA; (c) EDS spectrum of MgF₂-coated SMED/LCA; (d) EDS spectrum of Al₂O₃-coated SMED/LCA.

XRD analysis

The crystal phase of the prepared luminescent materials in fibers was determined by an XRD. As indicated in Figure 4(a), pure monoclinic diffraction peaks of luminescent fibers are predominant in the XRD patterns, which are similar to commercial Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphors. The diffraction pattern of SMED corresponds well to that of tetragonal Sr₂MgSi₂O₇ (PDF card no.75-1736) and hexagonal SiO₂ (PDF card no.86-1629). It might be that the excess SiO₂ of raw materials did not react completely. The XRD patterns of SMED/LCA contain sharp peaks at 17.5°, 28.5°, 30.7°, 35.8 and 43.5° 2θ, which agree with the diffraction peaks of SMED, indicating that the manufacturing process and the LCAs did not destroy the phase of SMED in the fiber. Figure 4(b) shows XRD patterns of coated SMED/LCA fibers, which are in good agreement with SMED/LCA without any impurity peaks. Obviously, the coating has no effect on the phase of SMED in the fibers. We believe that the characteristic XRD peaks of MgF₂ and Al₂O₃ in the XRD patterns of coated samples were not found because the coating MgF₂ and Al₂O₃ was amorphous. In summary, in the composite material, the crystal structure of the luminescence center is well preserved, which ensures the luminescence performance of the fiber.

Figure 4.

X-ray diffractometer (XRD) patterns of fibers and PDF card no.86-1629 and no.75-1736: (a) XRD patterns of fibers containing Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ (SMED) and SMED/light conversion agent (LCA) and PDF card no.86-1629 and no.75-1736; (b) XRD patterns of fibers containing SiO₂-coated SMED/LCA, Al₂O₃-coated SMED/LCA and MgF₂-coated SMED/LCA.

Fluorescence spectrum analysis

Figure 5 summarizes the photoluminescent properties of fibers containing different luminescent materials. The fluorescence emission spectrum of luminescent fibers was observed with 365 nm excited light, as shown in Figure 5(a). The fibers exhibit am emission peak at around 470 nm that overlaps with a broad emission band extending from 400 to 525 nm, which belongs to the typical 4f⁶5d¹–4f⁷ transition of Eu²⁺ in SMED. This indicates that SMED fiber can emit blue light.³⁵,³⁶ Under UV light excitation, the ground state electrons of Eu²⁺ ions are promoted to excited states. The excited electrons are subsequently trapped by electron traps through the conduction band. In the persistent luminescence process, the electrons trapped by shallow traps escape thermally via the conduction band and recombine with Eu²⁺, accompanied by blue long persistent luminescence. The LCA converts UV light and part of the blue light into red light. With the addition of the LCA, the emission peak intensity at 470 nm decreased, accompanied by an intense emission peak at 600 nm. The LCA has many conjugated structures, which absorb blue light and promote ground state electrons of conjugated structures to excited states, and emission peaking at 600 nm appears when the electrons return to the ground. The emission intensity of coated SMED/LCA fibers decreased, but the position of the emission peak is the same as that before coating. It may be concluded that the coating process does not destroy the phase of composite materials, as discussed earlier during study of the XRD patterns. The intensity ratio of red/blue shown in Figure 5(b) indicates the spectral color of fibers. The higher the intensity ratio, the redder the visual color. The high red/blue ratio indicates a successful color conversion process. The SMED fiber has a red/blue ratio of 0; because the phosphor has only one emission peak at 470 nm, the SMED/LCA fiber has a red/blue ratio of 4.2. We know that there will be a great loss in energy conversion when the spatial distance between the two materials is too large. The presence of the coated layer controls the spatial distance, ensuring that more blue light is converted into red light. So, the intensity ratio of Al₂O₃-coated SMED/LCA fiber is 5.8, which is an increase of about 1.4 times compared with SMED/LCA.

Figure 5.

Fluorescence emission spectrum and red/blue ratio (Int.600 nm versus Int.470 nm) of fibers containing different luminescent materials: (a) fluorescence emission spectrum of fibers; (b) red/blue ratio of fibers under ultraviolet excitation. SMED/LCA: Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/light conversion agent.

Afterglow spectrum analysis

Figure 6(a) shows the afterglow emission spectrum of fibers after UV excitation (365 nm) for 3 min. The fibers possess a bright afterglow persistent luminescence in the dark. SMED fiber possesses a blue peak at about 470 nm that comes from the typical afterglow emission of Eu²⁺ in SMED. SMED/LCA fiber exhibits two emission bands located at around 470 and 600 nm. The decrease in emission peak intensity at 470 nm can be attributed to the addition of the LCA; most of the light energy emitted by SMED is absorbed and reflected by the LCA to some extent, and there is energy loss between the two materials in the conversion process. It can be observed that the emission peak intensity decreases at 470 nm but increases at 600 nm with coated SMED/LCA fibers, indicating that more blue light is converted into red light. The closer the distance between the LCA and SMED, the greater the amount of light reaching the surface of the LCA. The coated layers realize the improvement of light energy conversion by reducing the shedding of the LCA from the surface of SMED. It can be seen from Figure 6(b) that the intensity ratio of MgF₂-coated SMED/LCA fiber increased by about 1.9 times compared with SMED/LCA fiber. To sum up, the coated layer can effectively reduce the shedding of the LCA from SMED during the spinning process, which improves the conversion efficiency of light color.

Figure 6.

Afterglow emission spectrum and red/blue ratio (Int.615 nm versus Int.470 nm) of fibers containing different luminescent materials: (a) afterglow emission spectrum of fibers; (b) red/blue ratio of samples under afterglow. SMED/LCA: Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/light conversion agent.

Decay of the afterglow

The afterglow decay curves of fibers containing SMED, SMED/LCA, SiO₂-coated SMED/LCA, Al₂O₃-coated SMED/LCA and MgF₂-coated SMED/LCA are shown in Figure 7(a). The afterglow decay of the luminescent fibers consists of a fast attenuation process in the first 300 s and a slow decay process later, which is determined by trap levels in different depths within SMED. The constant afterglow attenuation characteristics indicate to a certain extent that the LCA and the coated layer do not damage the structure of the phosphor. Figure 7(b) shows the afterglow initial brightness of the luminescent fibers. SMED fiber has an afterglow initial brightness of 0.2 cd/m²; however, for SMED/LCA fiber, the afterglow initial brightness is about 0.14 cd/m². Because the LCAs absorb and reflect part of the UV light energy and light energy emitted by SMED, there is energy loss between the SMED and LCAs in the conversion process. Besides, the afterglow brightness of coated SMED/LCA fibers also fluctuates slightly, which indicates that the coated layer has little effect on the afterglow characteristics of the SMED/LCA.

Figure 7.

Afterglow initial brightness and afterglow attenuation diagram of fibers containing different luminescent materials: (a) afterglow attenuation diagram of fibers; (b) afterglow initial brightness of fibers. SMED/LCA: Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/light conversion agent.

Figure 8.

CIE chromaticity diagram of luminescent fibers containing different materials. SMED/LCA: Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/light conversion agent.

Colorimetric analysis

Figure 8 shows the CIE 1931 chromaticity diagram for luminescent fibers under UV excitation (365 nm) and afterglow. Under the UV excitation, SMED fiber is located in the blue area; however, SMED/LCA fiber is located in the orange–red area because the LCA converts the blue light and exciting light into red light. In addition, the emission color of luminescent fibers is closer to a red color as the luminescent materials were coated by SiO₂, Al₂O₃ and MgF₂. After the UV excitation (365nm) for 3 min, the color coordinate of SMED/LCA fiber is located in the purple area, which is because the excitation light source of the LCA changes from two (UV light and blue light) to one (blue light), and the afterglow emission color of luminescent fibers has an obvious red shift as the luminescent material SMED/LCA has a coated layer. As mentioned above, the coated layer improves the light energy transmission of the LCA and SMED in the fiber, which increases the amount of red light. To observe the color tuning obtained from fibers directly, Figure 9 shows digital pictures of samples under indoor light and afterglow. We can see that the color of fibers under indoor light changes from white to red with the addition of the LCA component, while the afterglow color of samples changes from blue to purple. The color of SMED/LCA coated by SiO₂, Al₂O₃ and MgF₂ is basically unchanged under indoor light compared with SMED/LCA, but the afterglow color turns redder.

Figure 9.

Digital pictures of luminescent fibers containing different materials. SMED/LCA: Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/light conversion agent.

Conclusions

The light color of luminescent fiber is limited to the blue–green region due to the limitation of luminescent materials. In order to enrich the afterglow color and application range of luminescent fiber, we successfully prepared red luminescent fibers: SMED/LCA-PAN based on a multilayer structure. The surface morphology, phase structure and luminescence properties of the luminescent fibers were characterized.

Analysis of SEM and EDS demonstrates that a continuous and uniform SiO₂ (Al₂O₃ or MgF₂)-coated layer on the red phosphor surface is obtained, which means the coated layer can improve the stability of SMED/LCA in the fiber. The XRD pattern of the coated samples corresponds well with tetragonal Sr₂MgSi₂O₇ (PDF card no.75-1736), indicating that the coating process has no effect on the phase of SMED in the fibers. The CIE chromaticity diagram shows that the afterglow emission color of luminescent fibers has an obvious red shift as the luminescent material SMED/LCA has a coated layer. The color coordinates are located in the purple–red area, which means that the fiber has a purple–red long afterglow.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This work was supported by the Natural Science Foundation of Jiangsu Province (No. BK20171140, No. BK20180629), the National Natural Science Foundation of China (No. 51803076, 51803096) and the Open Project Program of the Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University (No. KLET 2004).

ORCID iDs

Zhu Yanan

Li Jing

References

Finley

Cobb

Duke

, et al. Optimizing blue persistent luminescence in (Sr1-delta Ba delta)(2) Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ via solid solution for use in point-of-care diagnostics. ACS Appl Mater Interface 2016; 8: 26956–26963.

Chen

, et al. Multidirectional effects of Sr‑, Mg‑, and Si-containing bioceramic coatings with high bonding strength on inflammation, osteoclastogenesis, and osteogenesis. ACS Appl Mater Interface 2014; 6: 4264–4276.

Zhang

Zhou

, et al. Fabrication and study of properties of the PLA/Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ long-persistent luminescence composite thin films. Mater Sci Semicond Proc 2015; 40: 130–135.

Qian

Liu

, et al. Three-dimensional printing of hybrid organic/inorganic composites with long persistence luminescence. Opt Mater Expr 2018; 8: 2823.

Zhu

MQ.

Effect of y/x ratio on luminescence properties of xSrO·yAl₂O₃:Eu²⁺,Dy³⁺ luminous fiber. J Rare Earth 2014; 32: 598–602.

Cui

Yang

Zhang

, et al. Round-the-clock photocatalytic hydrogen production with high efficiency by a long-afterglow material. Angewandte Chemie Int Ed 2019; 58: 1340–1344.

Ojha

Trautvetter

Norrbo

, et al. Sintered silica bodies with persistent luminescence. Scripta Materialia 2019; 166: 15–18.

Indermühle

Puzenat

Dappozze

, et al. Photocatalytic activity of titania deposited on luminous textiles for water treatment. J Photochem Photobiol A Chem 2018; 367: 67–75.

Jiang

Wang

Zhou

, et al. Optimization of strontium aluminate-based mechanoluminescence materials for occlusal examination of artificial tooth. Mater Sci Eng C 2018; 92: 374–380.

10.

Shi

Shen

Zhu

, et al. Excitation wavelength-dependent dual-mode luminescence emission for dynamic multicolor anticounterfeiting. ACS Appl Mater Interface 2019; 11: 18548–18554.

11.

Wang

Zhao

Moller

, et al. Interfacial reaction-driven formation of silica carbonate biomorphs with subcellular topographical features and their biological activity. ACS Appl Mater Interface 2015; 7: 23412–23417.

12.

Yang

Liu

, et al. Enhancement of luminescence properties of SrAl₂Si₂O₈: Eu³⁺ red phosphor. Ceram Int 2020; 46: 17376–17382.

13.

Zhu

Yang

Wang

, et al. Additive-free Y₂O₃:Eu³⁺ red-emitting transparent ceramic with superior thermal conductivity for high-power UV LEDs and UV LDs. J Eur Ceram Soc 2020; 40: 2426–2431.

14.

Tealdi

Chiodelli

, et al. Ionic conductivity in melilite-type silicates. J Mater Chem A 2013; 2: 907–910.

15.

Temperature dependent fluorescence properties and mid-infrared random lasing emission in Ho³⁺ and Tm³⁺ co-doped lead lanthanum zirconate titanate ceramics. Ceram Int 2020; 46: 19425–19430.

16.

Cheng

Wang

, et al. Wide-spectrum manipulation of triboelectrification-induced electroluminescence by long afterglow phosphors in elastomeric zinc sulfide composites. J Mater Chem C 2019; 7: 4567–4572.

17.

Zhu

Pang

Wang

, et al.

Research on the afterglow properties of red-emitting phosphor:SrAl₂O₄: Eu²

⁺,Dy³⁺/light conversion agent for red luminous fiber. J Mater Sci Mater Electron 2016; 27: 7554–7559.

18.

Tian

Wen

Fan

, et al. A thermochromic luminous polyurethane based on long persistent luminescent phosphors and thermochromic pigment. New J Chem 2018; 42: 5066–5070.

19.

Xia

, et al. Efficient blue to red afterglow tuning in a binary nanocomposite plastic film. Nanomaterials 2018; 8: 260.

20.

Zhang

Red long-lasting phosphorescence based on color conversion process.

Opt Mater 2013; 35: 451–455.

21.

Chen

Wang

Zeng

, et al. Long persistent composite phosphor CaAl₂O₄:Eu²⁺,Nd³⁺/Y₃Al₅O₁₂:Ce³⁺: a novel strategy to tune the colors of persistent luminescence. New J Chem 2016; 40: 485–491.

22.

Zhang

Tao

, et al

. Preparation and luminescent properties of SiO₂–Sr₄A1₁₄O₂₅:Eu²

⁺, Dy³⁺/light conversion agent phosphor for anti-counterfeiting application. J Mater Sci Mater Electron 2018; 29: 10762–10768.

23.

Zhu

MQ.

Effect of light conversion agent on the luminous properties of rare earth strontium aluminate luminous fiber.

J Mater Sci Mater Electron 2015; 27: 580–586.

24.

Chen

Cheng

, et al. Preparation and luminescent properties of multicolored SrAl₂O₄:Eu²⁺, Dy³⁺/SiO₂-coated red-emitting coumarin color converter/polyamide 6 luminous fiber with warm-toned luminescence. Text Res J 2020; 90: 1783–1791.

25.

Kumar

Kedawat

Kumar

, et al. Sunlight-activated Eu²⁺/Dy³⁺doped SrAl₂O₄ water resistant phosphorescent layer for optical display and defense applications. New J Chem 2015; 39: 3380–3387.

26.

Karacaoglu

Ozturk

Uyaner

, et al. Atomic layer deposition (ALD) of nanoscale coatings on SrAl₂O₄ based phosphor powders to prevent aqueous degradation. J Am Ceram Soc 2020; 103: 3706–3715.

27.

Yang

Liu

, et al. Rapid combustion method for surface modification of strontium aluminate phosphors with high water resistance. Appl Surf Sci 2012; 258: 6814–6818.

28.

Jaberi

Movahed

Ahmadpour

The study on titanium dioxide-silica binary mixture coated SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor as a photoluminescence pigment in a waterborne paint. J Fluores 2019; 29: 461–471.

29.

Rojas-Hernandez

Rubio-Marcos

Serrano

, et al. Boosting phosphorescence efficiency by crystal anisotropy in SrAl₂O₄:Eu,Dy textured ceramic layers. J Eur Ceram Soc 2019; 40: 1677–1683.

30.

Gagnidze

Walfort

, et al. Direct-epitaxial growth of SrAl₂O₄:Eu,Dy thin films on Al₂O₃ substrate by pulsed laser deposition. Appl Surf Sci 2019; 491: 53–59.

31.

Zhang

Tao

, et al. Spectral characteristics of Sr₂ZnSi₂O₇:Eu²⁺, Dy³⁺/PAN spectrum-fingerprint anti-counterfeiting fiber. Mater Res Expr 2018; 5: 085303.

32.

Jin

Shi

, et al. Preparation and luminescence studies of thermosensitive PAN luminous fiber based on the heat sensitive rose red TF-R1 thermochromic pigment. Dyes and Pigments 2017; 139: 693–700.

33.

Luo

Gao

Zhang

, et al

. Structure and luminescent properties of luminous polypropylene fiber based on Sr₂MgSi₂O₇:Eu²

⁺, Dy³⁺. J Rare Earth 2014; 32: 696–701.

34.

Xue

Shen

, et al

. Luminous properties of skin–core structure new luminous fiber: SrAl₂O₄:Eu²

⁺,Dy³⁺-PET/light conversion agent-PET. J Mater Sci Mater Electron 2018; 29: 18045–18050.

35.

Jorma

Taneli

Mika

, et al

. Defect aggregates in the Sr₂MgSi₂O₇ persistent luminescence material.

J Rare Earth 2011; 29: 1130–1136.

36.

Tshabalala

Swart

Dejene

, et al. Structure, surface analysis, photoluminescent properties and decay characteristics of Tb³⁺-Eu³⁺ co-activated Sr₂MgSi₂O₇ phosphor. Appl Surf Sci 2016; 360: 409–418.