Long-lasting Phosphor Research Articles

Enhanced photocatalytic decomposition of methylene blue and toluene gas with hydrothermally coated TiO2-supported on Ag–CaAl2O4:Eu2+, Nd3+ long-lasting phosphor

Enhanced photocatalytic decomposition of methylene blue and toluene gas with hydrothermally coated TiO2-supported on Ag–CaAl2O4:Eu2+, Nd3+ long-lasting phosphor

Optical Bioimaging and Therapy

Optical Bioimaging and Therapy

Red persistent luminescent Sr3Al2O5₋xSxCl2:Eu2+, Tm3+ phosphors based on lattice engineering

Research and development of persistent luminous phosphors for longer wavelengths, especially for red, is relatively limited, despite significant achievements in persistent luminescent materials for blue and green afterglow. This study uses high-temperature solid phase reactions to successfully prepare S2− doped Sr3Al2O5Cl2:Eu2+, Tm3+ red phosphors. After incorporating S2− into the original O lattice site, Rietveld's refinement of the prepared samples revealed that the occupancy of Tm3+ in the host lattice was optimized. The photoluminescence spectra of the samples showed that the emission is significantly redshifted from 610 to 630 nm as S2− content increases. The main reason for the redshift behavior is that incorporating S2− into the lattice increases crystal field splitting, positively affecting the centroid shift. Additionally, the afterglow of the S2− doped samples are enhanced, with stronger initial brightness and increased duration. This can be attributed to deeper trap energy levels and higher trap concentrations created after incorporating S2−, as confirmed by thermally stimulated luminescence measurements. Consequently, long-lasting red phosphors with brighter afterglow and longer duration were obtained by S2−doping. Possible mechanisms and detailed processes are presented and explained.

Photoluminescence and afterglow behavior of a new orange long-lasting borate phosphor Eu2+, Dy3+: NaSr4(BO3)3

A new long-lasting phosphor Eu2+, Dy3+: NaSr4(BO3)3 was obtained by high temperature solid state process. The phosphor displays typical 5 dd-4f transition of Eu2+ upon UV illumination with a broad emission centering around 588 nm, which is orange visible to the naked eye. Such an emission can be divided into 2 single emissions since the Eu2+ cations are located in two different crystallographic sites in the forms of [EuO6] and [EuO8]. An optimal doping concentration for Eu2+ cation is determined as 2 at% due to the quenching effect with increasing Eu2+ concentration. The critical distance between the luminescence center is determined around 14 Å. Afterglow behaviors are further observed for the prepared phosphors, which can be expressed by an empirical double exponential decay model. The sample 2% Eu/Dy: NaSr4(BO3)3 displays the best afterglow performance. The reason for such an afterglow performance is revealed by thermal stimulated luminescence (TSL) that the co-doped Dy cations offer large numbers of electron traps with suitable trap depth.

Photocatalytic Reaction Properties of TiO₂-Supported on the Long Lasting Phosphor: Sr₄Al14O25:Eu2+,Dy3.

The TiO₂/Sr4Al14O25:Eu2+,Dy3+ photocatalytic composite was prepared by depositing the nano-crystalline titanium dioxide layer on the long-lasting phosphor substrate of strontium aluminate, using a low-pressure chemical vapor deposition (LP-CVD). The photocatalysis characteristic was studied by examining the photodegradation of benzene (C6H6) gas under UV, visible light illumination, and in the darkness. The photocatalytic composite of TiO₂-deposited Sr₄Al14O25:Eu2+,Dy3+ showed an active photocatalytic reactivity under UV-light as well as visible-light illumination. The mechanism of the photocatalysis reaction for the TiO₂-deposited strontium aluminate phosphor composite was interpreted in point of the energy band structure and phosphorescent emission. The coupling of nanocrystalline TiO₂ with the strontium aluminate phosphor might result in an energy band bending at the interface of TiO₂/Sr₄Al14O25:Eu2+,Dy3+, making the titanium dioxide at the junction to be photo-reactive even in a visible wavelength region. In addition, the depth profile of Auger electron spectroscopy (AES) confirmed a possible formation of oxygen vacancies at the interface between TiO₂ and Sr₄Al14O25:Eu2+,Dy3+. Then, oxygen defects create extra electrons which may excited subsequently to the conduction band and participate in a photocatalytic reaction, resulting in an enhancement of the photodecomposition of benzene. The LP-CVD TiO₂-strontium aluminate phosphor was also photoactive in the darkness because of light emission from the long lasting phosphor. Also, the TiO₂-deposited Sr₄Al14O25:Eu2+,Dy3+ long lasting phosphor was analyzed by a XRD (X-ray diffraction), TEM (transmission electron microscopy), UV/visible spectroscopy and AES.

Ultraviolet Light-Responsive Photorheological Fluid for Sensors and Actuators Realized by Phosphorescence Effects and LSTM RNN

A photo-rheological fluid (PRF) is a smart fluid which exhibits different viscosity under UV irradiation. A PRF is comprehensively presented in this work, with particular focus on its responses under UV off/on conditions. The isomeric conversion from SP to MC and vice versa under UV off and on, respectively, showed unequal rates of transformation. As a result, a complex non-linear hysteretic response was observed. To be used indifferent types of sensors and actuators which can exploit its rheological properties, it is essential the PRF have linearized hysteresis behavior. To minimize the asymmetric non-linear hysteresis characteristics under UV on and off conditions, the well-known long-lasting phosphor SAO (SrAl2O4:Eu2+, Dy3+) was incorporated. The incorporation of SAO in the PRF improved the linearity of the PRF response, although the conversion rate was not identical under UV off/on conditions. The SAO particles were observed to settle over time due to phase splitting, undermining the usefulness of the SAO-PRF composite. Instead of improving the PRF response by further adjusting the PRF composite, a software approach based on Long Short-Term Memory Recurrent Neural Networks (LSTM RNN) was employed to model and compensate the asymmetric non-linear hysteresis response, ensuring the realization of sensors and actuators that exploit PRF as hardware.

Efficient energy storage and uvioresistant perovskite solar cells through insulating Y2O2S-based long-lasting phosphor layer

Perovskite solar cells (PSCs) attract widespread attention owing to its extremely high power conversion efficiency (PCE) and low-price fabrication processing. However, the high-power output is merely limited under sunlight illumination and nearly zero at a dark atmosphere, which may potentially hinder the commercial development and outdoor applications. In this work, we introduce an efficient and stable long-lasting phosphor layer, Y2O2S: Eu3+, Ti4+, Mg2+ enabling PSCs to achieve energy-storage function owing to its persistent photoelectric conversion. When sunlight illumination is turned off, the modified devices can still keep current output for 2 h. Besides, the modified devices demonstrate a considerable improvement of PCE, suppressed hysteretic effects, and highly prolonged light stability. The optimized PCE of 20.9% is obtained through elevated light-harvesting, optimized bandgap alignment, and depressed charge recombination provided by the YOS layer. The modified PSCs maintain 83% of their original PCE after aging in UV light for 100 h and retain 78% of their original PCE after 90 days in the oxygen and humid condition. This work represents a novel strategy on obtaining energy storage and uvioresistant PSCs.

Long-lasting CaAl2O4:Eu2+,Nd3+ phosphor-coupled g-C3N4 QDs composites for the round-the-clock photocatalytic methyl orange degradation

Long-lasting phosphors are a type of important materials that can release their stored energy in form of light after tuning off the excitation light source. Due to this unique luminescent property, combining a long-lasting phosphor and a suitable photocatalyst can keep the photocatalytic activity in the absence of the excitation light source. Here, a novel round-the-clock photocatalyst, combined the CaAl2O4:Eu2+,Nd3+ (CAOED) blue long-lasting phosphor with the g-C3N4 quantum dots (QDs), is reported for the first time. Our results reveal that when the excitation light is off, the photocatalytic degradation of methyl orange (MO) in the CAOED-coupled g-C3N4 QDs composites can continue for > 3 h, and come back its initial state after several time. Although the light intensity emitted from the CAOED is decreased with the increase of the delay time, the stored energy of the obtained photocatalyst can be recharged and recovered basing on the long-lasting decay curve, exhibiting the round-the-clock behavior. Our discussion reveal that this external irradiation-free photocatalytic activity is due to the long-lasting luminescence of the CAOED caused by the crystal lattice defects and the visible-light utilization and recombination rate of photo-generated carriers in the CAOED-coupled g-C3N4 QDs photocatalyst.

Afterglow, TL and OSL properties of Mn2+-doped ZnGa2O4 phosphor

Zinc gallate (ZnGa2O4) spinel ceramics doped with Mn2+ ions was prepared by a solid-state reaction at 1200 °C in air. Manganese concentration was equal to 0.05 mol.% of MnO with respect to ZnO. Ceramics produced in this way show an efficient green emission at about 505 nm under UV or X-ray excitations, which is caused by Mn2+ ions. This green emission is observed also as a relatively long afterglow (visible to the naked eye in the dark for about one hour) after switching-off the X-ray excitation. Time profiles of the beginning of glow and afterglow have been studied together with thermally stimulated (TSL) and optically stimulated (OSL) luminescence. Experimental results demonstrate a presence of few types of shallow and deep traps responsible for the observed afterglow and TSL/OSL emission of the material. The possibility of pulsed optical stimulation and time-resolved OSL characteristics of ZnGa2O4: Mn2+ has been reported for the first time. The presented results suggest the ZnGa2O4: Mn2+ spinel as a promising material for further fundamental research and possibility of application as a green long-lasting phosphor or storage phosphor for TSL/OSL radiation dosimetry.

Luminescent properties of a new cyan long afterglow phosphor CaSnO3:Lu3.

Persistent luminescence (PPL) materials have gained lots of attention and have been widely used in traffic signs, displays, medical diagnosis and architectural decoration. Single ion doped PPL materials with stable emission are excellent for practical applications, but it is difficult to cover the entire wavelength range. Here, a new cyan long-lasting phosphor CaSnO3:Lu3+ was successfully synthesized at 1200 °C by the conventional high temperature solid state method. From the X-ray photoelectron spectroscopy (XPS), it can be concluded that the Sn2+ ions exist in the crystal lattice because the doping of Lu3+ ions changes the valence state of the Sn ions. According to the thermally simulated luminescence (TSL), the continuous afterglow of CaSnO3:Lu3+ phosphors is produced by appropriate hole or electron traps, which are caused by doping the calcium stannate host with rare earth ions (Lu3+). The long-lasting phosphorescence (LLP) properties of the cyan phosphor were first discussed and the afterglow mechanism was expounded in detail. The excitation and the emission spectra of the phosphor revealed the characteristic broad peak of the Sn2+ ion. Typical afterglow behavior of the CaSnO3:Lu3+ phosphors was exhibited after power was turned off.

Thermoluminescence of the persistent-luminescence phosphor, BaAl2O4; A stuffed tridymite

BaAl2O4 is a stuffed tridymite used as a long-lasting phosphor. The thermoluminescence of BaAl2O4 prepared by solution-combustion is reported. Analysis of the sample using X-ray diffraction shows that it formed as a single phase compound with a hexagonal structure following annealing at 1200 °C. A broad photoluminescence emission band between 300 and 650 nm was detected due to excitation at 248 nm. The phosphor showed a natural TL peak at 102 °C for measurement at 1 oCs−1 and, when beta irradiated to 100 Gy, two broad peaks at 123 and 318 °C also for heating at 1 oCs−1. The analysis of the main glow peak at 123 °C suggests that it is a combination of several collocated peaks, that is, peaks embedded within each other. We resolved four such components labelled peaks 1 to 4. The thermoluminescence decreases with heating rate in a way consistent with thermal quenching whose activation energy was determined as ∼0.65eV using peak 3. Interestingly, this value of the activation energy for thermal quenching for BaAl2O4, a stuffed derivative of silica, is similar to literature values for quartz (a silica), suggesting that the recombination centre in the two cases may be similar.

Dynamic Phosphorescent Color of the Warm-Toned Long-Lasting Phosphor Composite PMMA/RECC@SAOED

A series of warm-toned long-lasting phosphor composite PMMA/RECC@SAOED were prepared by coating various concentrations of coumarin type red-emitting color converter (RECC) on the surface of yellowish-green emitting long-lasting phosphor SrAl2O4:Eu2+, Dy3+ (SAOED) with the aid of PMMA encapsulation. The specific dynamic variation process of the phosphorescent color of PMMA/RECC@SAOED composites in darkness was systematically investigated. Results indicate that the perceived phosphorescent color of PMMA/RECC@SAOED undergoes an overall gradual shift toward blue in darkness after the removal of the excitation light, and the extent of this shift increases gradually with the increase of RECC. This work provides new perspectives in producing warm-toned emitting phosphors and investigating luminescent color.

Design, synthesis and characterization of a novel bluish-green long-lasting phosphorescence phosphor BaLu2Si3O10:Eu2+, Nd3.

Through drawing upon a solid-state reaction, a newly proposed long-lasting phosphor BaLu2Si3O10:Eu2+, Nd3+ is presented and prepared in this work. The thermoluminescence properties of the phosphor are substantially extended, and the long-lasting phosphorescence behavior is markedly intensified by virtue of the consolidation of Nd3+ ions which serve as trap centers. In line with density functional theory calculations, the conduction band is mostly composed of Lu 5d states while the Ba 5d states only have a tiny contribution. We analyzed the relationship between the phosphor’s electronic structure and its optical properties. The photoluminescence emission spectrum shows a blue emitting band with a wide asymmetric property and an extremum of 426 nm, arising from the 5d–4f transitions of the Eu2+ ions which occupy the Ba and Lu sites. It is asserted that the long-lasting phosphorescence of the Eu2+ ions which take up both Ba and Lu sites stems from the special form of conduction band and the occupying environment of the emission center. Yet, they have different contributions and induce an interesting phenomenon in which the blue emitting phosphor shows a bluish-green phosphorescence. The long-lasting phosphorescence can last in excess of 6 h at the recognized intensity level (0.32 mcd m−2) after excitation for 10 min. This work provides a new way of thinking for the development of multicolored LLP materials. This work analyzes and sheds light on the specific courses and provides a likely mechanism for the process.

Alkaline-earth metal based MOFs with second scale long-lasting phosphor behavior

Three MOFs based on alkaline-earth metals and aromatic carboxylate linkers show blue fluorescence that turns into green long-lasting phosphorescence.

A new blue long-lasting phosphorescence phosphor Mg2SnO4:Bi3+: synthesis and luminescence properties

In this article, we synthesized a new long-lasting phosphor Mg2SnO4:Bi3+ by traditional high-temperature solid-state reaction method. The structure and luminescence properties were characterized using X-ray powder diffraction, photoluminescence spectra, phosphorescence spectra, decay curves and thermoluminescence curves. The results show that the phosphor can exhibit blue emission corresponding to 3P1–1S0 transition of Bi3+ under UV light excitation. After ceasing the excitation, blue phosphorescence can be observed. For the optimal phosphor its blue phosphorescence could be observed by human naked eyes in the dark even after 3 h. The thermoluminescence analysis reveals that three kinds of trapping centers exist in the phosphor, of which the ones at 329 and 359 K are responsible for the long-lasting phosphorescence at room temperature. Bi3+ ions took the sites of Mg2+ and Sn4+ forming three different types of emitting centers, and yielding charged impurity defects which acted as charge trap centers and partly stored the excitation energy.

Tm3+ doped barium molybdate: A potential long-lasting blue phosphor

Molybdates have applications in various fields such as phosphors, optical fibers, scintillators, magnets, sensors and catalysts. Thulium ion is an excellent blue activator and plays an important role in the design of persistent luminescent materials. This paper reports the investigation of the structural and luminescent properties of Barium Thulium Molybdate (Ba1−xTmx)MoO4 microcrystals (with x = 0, 0.01 or 0.03). The scheelite-type crystalline structure was identified from XRD and Raman studies. Under ultraviolet (359 nm) excitation, photoluminescence (PL) spectra present the characteristic emission bands at 453 nm and 545 nm which are due to the D12→F34 and D12→H34,5 transitions, respectively, from Tm3+ ions. Thermoluminescence (TL) measurements were performed with powdered samples previously irradiated with beta radiation. The depth of traps, associated with trap levels located inside the band-gap, was determined from TL data using different methods of glow curve analysis. The kinetic parameters, determined from thermoluminescent glow curves, provide evidence about a possible persistent luminescence emission from the (Ba0.97Tm0.03)MoO4 sample. This is a potential blue-light or ultraviolet long-lasting phosphor, with a trapping level lifetime, at room-temperature (300 K), of about 6 days.

Designing Single-Ion Magnets and Phosphorescent Materials with 1-Methylimidazole-5-carboxylate and Transition-Metal Ions.

Detailed structural, magnetic, and photoluminescence (PL) characterization of four new compounds based on 1-methylimidazole-5-carboxylate (mimc) ligand and transition metal ions, namely [Ni(mimc)2(H2O)4] (1), [Co(μ-mimc)2]n (2), {[Cu2(μ-mimc)4(H2O)]·2H2O}n (3), and [Cd(μ-mimc)2(H2O)]n (4) is reported. The structural diversity found in the family of compounds derives from the coordination versatility of the ligand, which coordinates as a terminal ligand to give a supramolecular network of monomeric entities in 1 or acts as a bridging linker to build isoreticular 2D coordination polymers (CPs) in 2-4. Magnetic direct-current (dc) susceptibility data have been measured for compounds 1-3 to analyze the exchange interactions among paramagnetic centers, which have been indeed supported by calculations based on broken symmetry (BS) and density functional theory (DFT) methodology. The temperature dependence of susceptibility and magnetization data of 2 are indicative of easy-plane anisotropy (D = +12.9 cm-1, E = +0.5 cm-1) that involves a bistable Ms = ±1/2 ground state. Alternating-current (ac) susceptibility curves exhibit field-induced single-ion magnet (SIM) behavior that occurs below 14 K, which is characterized by two spin relaxation processes of distinct nature: fast relaxation of single ions proceeding through multiple mechanisms (Ueff = 26 K) and a slow relaxation attributed to interactions along the polymeric crystal building. Exhaustive PL analysis of compound 4 in the solid state confirms low-temperature phosphorescent green emission consisting of radiative lifetimes in the range of 0.25-0.43 s, which explains the afterglow observed during about 1 s after the removal of the UV source. Time-dependent DFT and computational calculations to estimate phosphorescent vertical transitions have been also employed to provide an accurate description of the PL performance of this long-lasting phosphor.

Luminescence properties of a novel bluish green long-lasting phosphor LiBaPO4: Eu2+, Ho3+

A novel bluish green long-lasting phosphor LiBaPO4: Eu2+, Ho3+ was synthesized by solid-state reaction. The phosphor was characterized by X-ray diffraction, photoluminescence spectra, afterglow decay curve and thermoluminescence spectrum. The photoluminescence is ascribed to the 5d-4f transitions of Eu2+ ions. There is no Ho3+ emission in the photoluminescence spectra, which means that Ho3+ is a coactivator. After irradiated with a UV light (365nm), persistent luminescence can last more than 5626s above 0.32mcd/m2, which is 100 times than the sensitivity of human eyes in dark. Thermoluminescence curves indicate that only one trap depth in the phosphor, which is ascribed to the doping of Ho3+. The possible mechanism of persistent luminescence was discussed.

Preparing, Characterizing, and Investigating Luminescent Properties of a Series of Long-Lasting Phosphors in a SrO–Al2O3 System: An Integrated and Inquiry-Based Experiment in Solid State Chemistry for the Undergraduate Laboratory

An integrated and inquiry-based experiment on solid state chemistry is applied to an inorganic chemistry lab course to provide insight into the characteristics of the solid phase reaction. In this experiment, students have the opportunity to synthesize long-lasting phosphors with formula xSrO·yAl2O3:Eu2+, Dy3+, by means of precipitation and high temperature methods, and to characterize them by powder X-ray diffractometry. The luminescent properties of the phosphors are also suitable for investigation by student research teams with the assistance of solid fluorescence analysis. With a change in the Sr/Al ratio of strontium aluminates, the phosphors show distinct emission bands, and with a change in the content of Dy in a certain range, the different data of luminescence intensity and decay time can be obtained. By analyzing the crystal structures and photoluminescence mechanism of products, students can better understand abstract concepts of luminescent solid materials, including nonstoichiometric compound...

Preparation of color tuned highly emissive long-lasting phosphor with warm-toned emitting color based on coating red-emitting coumarin fluorescent dye color converter and PMMA on SrAl2O4:Eu2+, Dy3+ phosphor

A color tuned highly emissive long-lasting phosphor PMMA/RECC@SAOED with warm-toned emitting color was prepared by coating a red-emitting coumarin fluorescent dye color converter (RECC) and PMMA on the surface of green emitting SrAl2O4:Eu2+, Dy3+ (SAOED) phosphors. After being characterized by SEM, FT-IR spectra, photoluminescence (PL) spectra, CIE color coordinates and afterglow decaying curve, the results demonstrated the feasibility of the prepared RECC as the warm-toned color converter for the green-emitting SAOED. After being coated with color converter, the PL spectra of PMMA/RECC @SAOED consisted of two broad bands with two emission peaks at 520 nm and 610 nm, and the intensity of spectra in the range of (576–700) nm increased gradually with the increase of color converter content. The emitting color of the PMMA/RECC@SAOED could be easily controlled by adjusting the concentration of color converter, and it moved to yellow, orange and reddish when the concentration of color converter was added to 0.3%, 0.5% and 0.9%.