Persistent Photoluminescence Research Articles

Persistent Photoluminescence and Mechanoluminescence of a Highly Sensitive Pressure and Temperature Gauge in Combination with a 3D-Printable Optical Coding Platform.

Distinct types of luminescence that are activated by various stimuli in a single material offer exciting developmental opportunities for functional materials. A versatile sensing platform that exhibits photoluminescence (PL), persistent luminescence (PersL), and mechanoluminescence (ML) is introduced, which enables the sensitive detection of temperature, pressure, and force/stress. The developed Sr2MgSi2O7:Eu2+/Dy3+ material exhibits a linear relationship between ML intensity and force and can be used as an ML stress sensor. Additionally, the bandwidth of the PL emission band and the PL lifetime of this material are remarkably sensitive to temperature, with values of ≈0.05nmK-1 and 1.29%/K, respectively. This study demonstrates PersL pressure sensing for the first time, using long-lasting (seconds) lifetime as a manometric parameter. The developed material functions as an exceptionally sensitive triple-mode visual pressure sensor; specifically, it exhibits: i) a sensitivity of ≈-297.4cmGPa-1 (8.11nmGPa-1) in bandshift mode, ii) a sensitivity of ≈272.7cm-1/GPa (14.8nmGPa-1) in bandwidth mode, and iii) a sensitivity of 42%GPa-1 in PL-lifetime mode, which is the highest value reported to date. Notably, anti-counterfeiting, night-vision safety-sign, 8-bit optical-coding, and QR-code applications that exhibit intense PersL are demonstrated by 3D-printing the studied material in combination with a polymer.

Silica nanoparticle-reinforced polyurethane plastic immobilized with strontium aluminate nanofiller: Ultraviolet protection, superhydrophobicity and photoluminescence

A simple strategy was reported toward a possible industrial preparation of smart plastic materials with persistent afterglow, ultraviolet protection, superhydrophobic properties and photochromism. Nanoparticles of rare-earth doped aluminate (NREA) were embedded into a polyurethane plastic composite. A combination of polyurethane (bulk material), silica nanoparticles (nanofiller), and NREA (luminous agent) was prepared. Achieving a uniform distribution of NREA in a polyurethane fluid allows for the manufactured plastic to be colorless. NREA showed diameters between 12 nm and 26 nm. When excited at 365 nm, the produced photoluminescent polyurethane composite demonstrated an emission band at 519 nm. NREA contents more than 1 % were found to exhibit persistent photoluminescence, whereas pigment concentrations less than 1 % were found to exhibit fluorescence emission. The created plastic concrete exhibited photochromism, as shown by the coloration parameters and photoluminescence spectra, which proved a change in color between transparent during daylight, green under ultraviolet rays, and greenish-yellow in darkness. The static contact angle tests demonstrated effective superhydrophobic properties. Significant improvements were detected ultraviolet protection and photostability. The hardness properties, structural compositions, and morphology of the developed polyurethane plastics were also explored.

Surface-silanized glass nanofibers and aluminate nanoparticles as reinforcing agents for acrylic emulsion toward multifunctional stimuli-responsive composite coatings

Smart waterborne coatings have shown various functions, such as afterglow photoluminescence, antimicrobial activity, water resistance, ultraviolet blocking, and anti-counterfeiting properties. However, photoluminescent organic agents have shown poor photostability and high cost. Additionally, waterborne acrylic coatings have shown poor mechanical properties. Herein, nanoparticles of rare-earth strontium aluminate (NRESA) and electrospun glass nanofibers (EGN) were used to strengthen the bulk of acrylic (ACR) coatings to develop smart products with mechanical reliability, hydrophobicity, ultraviolet blocking, and persistent photoluminescence. By physically integrating nano-scaled particles of RESA, colorless smart coatings of EGN@ACR were produced. Photoluminescence spectra showed that the transparent EGN@ACR changed its appearance to greenish when exposed to ultraviolet rays. Hybrids of EGN@ACR with trace amounts of NRESA showed fluorescence emission with instant reversibility. As the phosphor concentration in the EGN@ACR hybrids increased, afterglow photoluminescence with delayed reversibility was detected. When excited at 370 nm, the hybrid coatings displayed an emission band at 519 nm. The morphological analysis of NRESA by transmission electron microscopy (TEM) displayed diameters of 9–21 nm. After being prepared using electrospinning technology, glass nanofibers were introduced into acrylic emulsion coatings as a reinforcement agent. Scanning electron microscopic (SEM) analysis of EGN showed diameters of 70–120 nm. The smart coatings had better resistance to scratches as compared to the control sample of NRESA-free acrylic paint. A higher concentration of NRESA resulted in enhanced hydrophobicity and ultraviolet blocking.

Preparation of glass nanofibers to reinforce polymethyl methacrylate toward persistent photoluminescent bricks

Polymethyl methacrylate (PMMA) was subjected to a reinforcement process by using electrospun glass nanofibers (GNF) to produce durable and transparent bricks. Photoluminescent and photochromic GNF@PMMA bricks were prepared by physical incorporation of lanthanide-activated aluminum strontium oxide (LASO) nanoparticles (NPs). Both CIE (Commission internationale de l'éclairage) Lab parameters and photoluminescence analysis were investigated to verify transparency of GNF@PMMA with the capability to change to green under UV lighting. The photochromic property was instantaneously reversible for GNF@PMMA hybrid bricks with low concentrations of LASO NPs, demonstrating fluorescence emission. GNF@PMMA with high concentrations of LASO NPs exhibited persistent photoluminescence afterglow emission with slower reversibility. An emission peak was detected at 517 nm upon excitation at 365 nm. Both hydrophobicity and ultraviolet shielding improved as LASO NPs content increased. Both of X-ray diffraction (XRD) and transmission electron microscopic analysis (TEM) were applied to examine the morphological features of LASO NPs and GNF to show diameters of 10–19 nm and 100–250 nm, respectively. Electrospinning technology was applied to prepare GNF, which were used to reinforce PMMA bricks as a roughening agent to improve their mechanical properties. Different analytical methods were utilized to analyze GNF and GNF@PMMA bricks for their morphological features. The scratching resistance of LASO NPs-containing GNF@PMMA bricks improved as compared to LASO NPs-free GNF@PMMA.

Development of glow-in-the-dark and color-tunable poly(methyl methacrylate) plastic concrete immobilized with rare-earth aluminate

A simple method is reported for the prospective industrial production of lightweight poly(methyl methacrylate) (PMMA) plastic concrete with persistent afterglow. Nanoparticles (NPs) of lanthanide activated aluminate (LAA) pigment were molded into a plastic bar. With the uniform dispersion of LAA NPs in the plastic fluid, the produced plastic bar can be made transparent. was A simple polymerization of methyl methacrylate (MMA; bulk material) blended with silica nanoparticles (filler), and LAA nanoparticles (luminous agent) was applied in the presence of 2,2-azobisisobutyronitrile (AIBN) catalyst to provide photoluminescent PMMA plastic concrete. In studies, LAA NPs were found to have sizes between 9 and 95 nm. When excited at 369 nm, the luminescent PMMA concrete displayed an emission peak at 518 nm. For pigment concentrations over 1%, persistent photoluminescence was observed, whereas fluorescence was tracked for the LAA contents equal to or below 1%. The manufactured plastic concrete was shown to exhibit photochromism from colorless under daytime light to green below UV, and greenish-yellow in the dark. By measuring the static contact angle, we were able to confirm the excellent superhydrophobic activity. Indications of enhanced UV protection and photostability were monitored upon increasing LAA ratio in the concrete bulk. Strong durability, reversibility and continuous afterglow emission were hallmarks of the photoluminescent hard composite concrete. The created plastic concrete morphology, elemental content and hardness properties were studied.

Persistent triboelectrification-induced electroluminescence for self-powered all-optical wireless user identification and multi-mode anti-counterfeiting.

Persistent triboelectrification-induced electroluminescence (TIEL) is highly desirable to break the constraints in the transient-emitting behavior of existing TIEL technologies as it addresses the hindrance caused by incomplete information in optical communication. In this work, a novel self-powered persistent TIEL material (SP-PTM) has been created for the first time, by incorporating the long-afterglow phosphors SrAl2O4:Eu2+, Dy3+ (SAOED) in the material design. It was found that the blue-green transient TIEL derived from ZnS:Cu, Al serves as a reliable excitation source to trigger the persistent photoluminescence (PL) of SAOED. Notably, the aligned dipole moment formed along the vertical direction in the bottom ferroelectric ceramics layer acts as an "optical antenna" to promote variation in the electric field of the upper luminescent layer. Accordingly, the SP-PTM exhibits intense and persistent TIEL for about 10 s in the absence of a continuous power supply. Due to such unique TIEL afterglow behavior, the SP-PTM is applicable in many fields, such as user identification and multi-mode anti-counterfeiting. The SP-PTM proposed in this work not only represents a breakthrough in TIEL materials due to its recording capability and versatile responsivity but also contributes a new strategy to the development of high-performance mechanical-light energy-conversion systems, which may inspire various functional applications.

Preparation of transparent photoluminescence plastic concrete integrated with lanthanide aluminate

A simple strategy was presented for potential industrial preparation of persistent afterglow lightweight plastic concrete toward smart hard surfaces. Rare-earth activated aluminate (REA) pigment nanoparticles (NPs) were integrated into plastic bar. The transparency of the prepared plastic bar can be achieved by consistent distribution of REA NPs in the plastic fluid. Unsaturated polyester resin (bulk material) was mixed with silica nanoparticles (filler) and REA NPs (luminescent agent) using methyl ethyl ketone peroxide as hardener. The curing process was accomplished for a few minutes at room temperature. The diameters of REA NPs were reported in the range of 6–11 nm. The phosphor-concrete composite can be industrially applied onto a variety of hard surfaces. The photoluminescent plastic concrete showed an emission band at 515 nm upon excitation at 372 nm. Persistent photoluminescence was detected for pigment concentrations higher than 1%, whereas fluorescence emission was monitored for pigment concentrations equal to 1%. Photochromism was observed for the prepared plastic concrete as different colors were detected under different light conditions, including colorless under daytime light, green underneath UV rays, and greenish-yellow under darkness as proved by luminescence spectra and CIE Lab parameters. The static contact angle measurements proved good superhydrophobic activity. An improved UV protection and photostability were detected. The photoluminescent hard composite concrete displayed highly durability and reversible persistent afterglow emission. The morphology, elemental composition and hardness features of the prepared plastic concrete were investigated.

Spin-orbital coupling and slow phonon effects enabled persistent photoluminescence in organic crystal under isomer doping

When periodically packing the intramolecular donor-acceptor structures to form ferroelectric-like lattice identified by second harmonic generation, our CD49 molecular crystal shows long-wavelength persistent photoluminescence peaked at 542 nm with the lifetime of 0.43 s, in addition to the short-wavelength prompt photoluminescence peaked at 363 nm with the lifetime of 0.45 ns. Interestingly, the long-wavelength persistent photoluminescence demonstrates magnetic field effects, showing as crystalline intermolecular charge-transfer excitons with singlet spin characteristics formed within ferroelectric-like lattice based on internal minority/majority carrier-balancing mechanism activated by isomer doping effects towards increasing electron-hole pairing probability. Our photoinduced Raman spectroscopy reveals the unusual slow relaxation of photoexcited lattice vibrations, indicating slow phonon effects occurring in ferroelectric-like lattice. Here, we show that crystalline intermolecular charge-transfer excitons are interacted with ferroelectric-like lattice, leading to exciton-lattice coupling within periodically packed intramolecular donor-acceptor structures to evolve ultralong-lived crystalline light-emitting states through slow phonon effects in ferroelectric light-emitting organic crystal.

Transient and Persistent Room‐Temperature Mechanoluminescence from a White‐Light‐Emitting AIEgen with Tricolor Emission Switching Triggered by Light

Persistent luminescence from purely organic materials is basically triggered by light and electricity, which largely confines its practical applications. A purely organic AIEgen exhibits not only persistent photoluminescence, but also transient and persistent room-temperature mechanoluminescence. By simply turning on and off a UV lamp, tricolor emission switching between blue, white, and yellow was achieved. The data from single-crystal structure analysis and theoretical calculation suggest that mechanism of the observed persistent mechanoluminescence (pML) is correlated with the strong spin-orbit coupling of the bromine atom, as well as the formation of H-aggregates and restriction of intramolecular motions in noncentrosymmetric crystal structure. These results outline a fundamental principle for the development of new pML materials, providing an important step forward in expanding the application scope of persistent luminescence.

Transient and Persistent Room‐Temperature Mechanoluminescence from a White‐Light‐Emitting AIEgen with Tricolor Emission Switching Triggered by Light

AbstractPersistent luminescence from purely organic materials is basically triggered by light and electricity, which largely confines its practical applications. A purely organic AIEgen exhibits not only persistent photoluminescence, but also transient and persistent room‐temperature mechanoluminescence. By simply turning on and off a UV lamp, tricolor emission switching between blue, white, and yellow was achieved. The data from single‐crystal structure analysis and theoretical calculation suggest that mechanism of the observed persistent mechanoluminescence (pML) is correlated with the strong spin–orbit coupling of the bromine atom, as well as the formation of H‐aggregates and restriction of intramolecular motions in noncentrosymmetric crystal structure. These results outline a fundamental principle for the development of new pML materials, providing an important step forward in expanding the application scope of persistent luminescence.

Persistent photoluminescence emission from SrTa2O6:Pr3+ phosphor prepared at different temperatures

Phosphors with persistent emission are of interest for security and emergency signage, and medical diagnosis. Three SrTa2O6:Pr3+phosphor samples with persistent emission were prepared by solid state reaction at 1200, 1400 and 1500°C. Structural crystallization was shown to improve with an increase in temperature as identified by X-ray diffraction. The scanning electron microscopy images showed that the particles of the phosphor were agglomerated and co-melting was induced by increasing the synthesis temperature. The ion distribution in the phosphors was determined using the time of flight secondary ion mass spectroscopy. The red emission was obtained from the D2→3H4 and the 3P0→3H6 transitions at 608 and 619nm, respectively. The main absorption occurred at 225nm (5.5eV), and the band gap (Eg) calculations confirmed that it corresponds to band-to-band excitation. Another excitation due to charge transfer at 300nm was also obtained which makes the phosphor suitable to be used in red light emitting diodes. The persistent emission time parameters (260–296s) were calculated from the phosphorescence decay curves using the second order exponential decay equation. The corresponding electron trapping centers were determined using the thermoluminescence spectroscopy, and the activation energy was determined using the initial rise method.

Mechanoluminescence of Persistent Luminescent SrAl$lt;inf$gt;2$lt;/inf$gt;O$lt;inf$gt;4$lt;/inf$gt;: (Eu$lt;sup$gt;2+$lt;/sup$gt;, Dy$lt;sup$gt;3+$lt;/sup$gt;) Material Prepared by Electron Beam Reduction

Long persistent luminescent SrAl2O4: (Eu, Dy) was prepared by electron beam reduction. The asprepared material was mechanically ball-milled into fine powder, and the powder was mixed with wear resistant epoxy resin. Then, the epoxy resin mixed persistent luminescent was coated on quartz glass plate by screen printing with thickness of about 1000 nm. The mechanoluminescent properties of the as-persistent luminescence film was characterized by falling ball impact technique with a homemade device for measuring mechanoluminescence intensity based on a single avalanche diode and a pico-amper meter. It is found that electron beam reduced SrAl2O4: (Eu, Dy) shows strong mechanoluminescence with high signal/background ratio of 1.25 and high signal/noise ratio. Further study found that intensity of the mechanoluminescence produced was proportional to exponential of the initial height of the ball (i.e., the final kinetic energy of the ball before impact) before falling down, and a decay curve was similar to that of persistent photoluminescence. These results indicate that mechanoluminescence is caused by impact energy of the ball which promotes electrons into traps, and then release via normal long persistent luminescent.

Ce3+/Pr3+: YAGG: A Long Persistent Phosphor Activated by Blue‐Light

The requirement of using ultraviolet light to stimulate afterglow luminescence has seriously restricted indoors/outdoors applications of most persistent materials developed hitherto. Herein, efficient blue‐light‐activated Ce3+, Pr3+: YAGG phosphors, showing optimized long‐persistent luminescence lasting for 1 h, were prepared and investigated in detail with the aid of X‐ray diffraction refinement, steady‐state/persistent photoluminescence spectra, room/low‐temperature persistent decay curves, and three‐dimensional thermo‐luminescence spectra. Notably, the afterglow properties were found highly dependent on the Ga content which greatly alters both the host band gap energy and the Ce3+: 5d level structure and thus is beneficial to the electrons' photoionization and trapping processes. Moreover, Pr3+ additive was found not only prolonged the afterglow lifetime of Ce3+ through improving concentration of carriers captured at the trap, but also served as the red‐emissive centers for color tuning. The persistent energy transfer from Ce3+ to Pr3+ was experimentally demonstrated for the first time.

Fluorescence Resonance Energy Transfer Inhibition Assay for α-Fetoprotein Excreted during Cancer Cell Growth Using Functionalized Persistent Luminescence Nanoparticles

Persistent-luminescence nanoparticles (PLNPs) are promising as a new generation of photoluminescent probes for detection of biomolecules and bioimaging. Here we report a fluorescence resonance energy transfer (FRET) inhibition assay for α-fetoprotein (AFP) excreted during cancer cell growth using water-soluble functionalized PLNPs based on Eu2+- and Dy3+-doped Ca1.86Mg0.14ZnSi2O7. Polyethyleneimine-coated PLNPs were conjugated with AFP-antibody-coated gold nanoparticles as a sensitive and specific persistent photoluminescence probe for detection of AFP in serum samples and imaging of AFP excreted during cancer cell growth. Such PLNPs do not contain toxic heavy metals. Their long-lasting afterglow nature allows detection and imaging without external illumination, thereby eliminating the autofluorescence and scattering light from biological matrixes encountered under in situ excitation.

Er3+-doped Nanoparticles for Optical Detection of Magnetic Field

A bright persistent photoluminescence has been observed in Er(3+)-doped nanoparticles prepared by selective dissolution of bulk oxyfluoride nano-glass-ceramics. A 2 orders of magnitude decrease of intensity of the (4)S(3/2)-->(4)I(15/2) green emission band of Er(3+) in these nanoparticles is observed in magnetic fields up to 50 T. This strong luminescence sensitivity to magnetic field can be used for localization and distant optical detection of magnetic field in nanovolumes with a field-resolution of 0.01 T.

GaN quantum dots doped with Eu

Molecular-beam-epitaxy growth of Eu-doped GaN quantum dots embedded in AlN has been achieved. The crucial issue of Eu location has been addressed by extended x-ray absorption fine structure measurements. By comparing the signature of the Eu short-range environment for several samples, it is concluded that Eu is mostly incorporated in GaN dots. Intense cathodoluminescence associated with Eu has been measured, with no GaN bandedge emission, evidence that carrier recombination mostly occurs through rare-earth ion excitation. Persistent photoluminescence of Eu-doped GaN quantum dots as a function of the temperature is suggested to be further confirmation of the recombination of confined carriers through Eu ion excitation.

Persistent photoluminescence in high-purity GaN

High-purity GaN grown by hydride vapor-phase epitaxy was studied by time-resolved photoluminescence (PL). Two types of samples, 6–30-μm-thick GaN layers on sapphire substrate and a 200-μm-thick freestanding template, exhibited similar PL behavior. At low temperatures, the luminescence signal from the red, yellow, blue, and ultraviolet luminescence bands could be detected at delay times up to several minutes following excitation light pulse. The persistent PL in freestanding template can be attributed solely to a donor–acceptor-pair-type recombination in very pure GaN. However, a similar slow decay of radiative transitions in apparently less-pure GaN films on sapphire raises the possibility of additional mechanisms for the observed persistent PL.

Structural and Optical Properties of GaN Quantum Dots

ABSTRACTGrowth conditions, structural and optical properties of GaN quantum dots (QDs) grown by plasma-assisted molecular beam epitaxy will be examined. It will be shown that, depending on the Ga/N ratio value and on growth temperature, the growth mode of GaN deposited on AlN can be either of the Stranski-Krastanow or of the Frank-Van der Merwe type. It will be shown that vertical correlation results in a red shift and in a narrowing of the photoluminescence spectra.Growth of Eu-doped GaN quantum dots embedded in AlN will be described. Intense photoluminescence associated with Eu has been measured, with no GaN band-edge emission, as an evidence that carrier recombination mostly occurs through rare earth ion excitation. Persistent photoluminescence of Eu-doped GaN quantum dots as a function of temperature has been put in evidence, as a further confirmation of the recombination of confined carriers through Eu ion excitation.

Strong visible photoluminescence from SiO2 nanotubes at room temperature

The optical studies of SiO2 mesoporous materials with hierarchical tubules-within-tubule structure have been investigated by photoluminescence and Fourier-transform infrared transmittance (FTIR). Our results suggest that the radiative intensity can be strongly enhanced by annealing the samples in N2 environment. From the FTIR spectra, we have pointed out that the origin responsible for the strong emission is Si–OH complexes located on nanotube surface. It has been observed that after turning off the pumping laser, the photoluminescence signal of SiO2 nanotubes can persist for several seconds, which is much longer than that of most materials performed under similar conditions. We have found that the decay of the photoluminescence signal is due to the quantum tunneling process. These are triplet and singlet states of Si–OH complexes that are responsible for the observed persistent photoluminescence.

Observation of persistent photoluminescence in porous silicon: Evidence of surface emission

We report on the observation of persistent photoluminescence (PPL) in oxidized porous silicon. The PPL decay can be well described by a stretched-exponential function, and its decay rate is not sensitive to the change of temperature. We point out that the PPL behavior can be interpreted in terms of the picture that the emission arises from the excited surface complexes, which is produced by capture of photocarriers tunneling from the nearest shallow trap in the nanocrystalline silicon. To explore the microscopic origin of the surface compounds, we performed infrared absorption, and found that the PPL intensity correlates well with Si–OH vibration mode. Further evidence is provided by the recent theoretical calculation showing that the Si–OH complex can emit the photon energy in the range observed here. We thus provide concrete evidence to support the fact that the PL signal of porous silicon does contain surface emission.