Conversion Luminescence Research Articles

Luminescent converters based on nanocellulose + K3Tb(PO4)2:Eu composite films

The advantages of cellulose and its derivatives as the latest materials for devices that generate, store, and convert electricity are their low cost, environmental friendliness, ease of recycling and the ability to be manufactured in various ways and from various raw materials, including agricultural waste. This predetermines the relevance of their study as materials for modern technology and electronics. The research aims to determine the luminescent characteristics of composite films made based on nanocellulose and polycrystalline oxide K3Tb0.9Eu0.1(PO4)2. Optical microscopy and the spectral-luminescence method were used to characterise the films and their initial components. It was found that crystallites with an average size of about 50mm are distributed quite evenly in the film “nanocellulose+K3Tb0.9Eu0.1(PO4)2”. A Raman scattering band with a maximum of 564 nm under laser excitation at 473 nm was observed for the investigated samples in the form of suspensions. The intensity of photoluminescence of nanocellulose in suspension and films is low compared to the luminescence of oxide as a filler. The luminescence of Eu3+ ions is intense in the red region of the spectrum. The calculated values of the degree of asymmetry indicate low symmetry of the positions occupied by europium ions in the oxide and the contribution of Tb3+ ion emission to the overall spectrum of the composite film. The study results show that the luminescence of Eu3+ ions is sensitised by Tb3+ ions, which absorb the excitation light and then transfer energy to europium ions. The position of the absorption bands of Eu3+ and Tb3+ ions in the ultraviolet region of the spectrum and the intense emission of Eu3+ in the red region indicates the prospects of using nanocellulose+ K3Tb0.9Eu0.1(PO4)2 films to improve the efficiency of solar panels. Testing of the films under the excitation of luminescence by ultraviolet radiation of an LED (λex=375 nm) showed the possibility of developing white LEDs on their basis. In particular, the chromaticity coordinates of the uncoated LED were (x=0.214; y=0.079), and the use of a film composite as a coating causes a shift in the coordinates to the red region: x=0.304, y=0.196. The obtained results on the morphology and luminescent properties can be used to optimise the composition and manufacturing conditions of composite films of the following types “nanocellulose+K3Tb0.9Eu0.1(PO4)2” for use as fluorescent converters in LEDs or solar panels

Deep‐Red Ca3Al2Ge3O12:Eu3+ Garnet Phosphor with Near‐Unity Internal Quantum Efficiency and High Thermal Stability for Plant Growth Application

AbstractTrivalent europium (Eu3+) doped phosphors usually radiate orange or red light owing to distinct transitions from the 5D0 excited level to the ground states of 7F1 and 7F2. However, Eu3+ activated phosphors with a dominant deep‐red emission due to 5D0→7F4 transition are relatively rare. In this work, the synthesis and photoluminescence properties of Ca3Al2Ge3O12:Eu3+ deep‐red phosphor with an intense 5D0→7F4 transition are reported. Irradiating this new garnet phosphor with 394 nm near‐ultraviolet light generates a dominant deep‐red emission band centered at 707 nm. The phosphor has a high internal quantum efficiency of 98.4% and excellent luminescence thermal stability, maintaining 78.8% of the room temperature emission intensity at 150 °C. Based on the unique spectral feature of this new compound, a phosphor‐converted deep‐red LED prototype device is fabricated, producing an output power of 27.3 mW with a photoelectric conversion efficiency of 4.0% at 200 mA. Plant growth experiments are also conducted to demonstrate the obvious positive effects of the fabricated deep‐red LED on plant growth, further indicating that the as‐prepared Ca3Al2Ge3O12:Eu3+ deep‐red phosphor can act as a promising luminescence converter for plant growth LED bulbs.

Enhanced Luminescent Performance via Passivation of Surface Undercoordinated Pb Atoms in a CsPbBr3 Microplate

AbstractPerovskite materials are widely used in the fields of luminescence and light energy conversion with the advantages of low cost and outstanding optoelectronic properties. However, abundant surface lattice defects heavily affect the performances of perovskite optoelectronic devices. Here, by treating surface defects with oleylamine molecules in situ, the surface trap states are significantly decreased in a CsPbBr3 microplate, enabling photoluminescence intensity and carrier lifetimes to be dramatically enhanced and prolonged, respectively. These interesting phenomena can be attributed to the binding of undercoordinated Pb atoms with N atoms on the surface of perovskite microplate. The strong binding energy of lead‐halogen bonds inhibits the photodegraded reactions of the crystal, leading to the significant improvement of luminescent stability for the microplate correspondingly. The results not only provide experimental guidance for passivating lattice defects but also pave the way for improving the efficiency of wide materials and optoelectronic devices.

Multicolor and multimode luminescence regulation and anti-counterfeiting application of lanthanide ions doped Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> phosphors

Multicolor and multimode luminescence materials have important applications in the field of information security encryption. However, the design and synthesis of multicolor multimode luminescent materials is still a challenge, and only several materials have been reported. In this paper, a series of single doped and double doped Li<sub>1–<i>x</i></sub>K<sub><i>x</i></sub>NbO<sub>3</sub>:Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup> phosphors are prepared by high temperature solid state method. The structure, morphology, optical properties and thermoluminescence (TL) spectra are characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), luminescence spectrometer and self-made heating device. Firstly, the effects of different values of K<sup>+</sup> content on the luminescence and trap distribution of LiNbO<sub>3</sub> materials are studied. The results show that the ionic lattice is distorted when a small quantity of K<sup>+</sup> ions replace Li<sup>+</sup>. With the addition of K<sup>+</sup>, the photoluminescence excitation (PLE) spectra monitored emission of 620 nm shows that the ratios of the absorption peaks from matrix (200–310 nm) to absorption peaks from the intrinsic transition of Pr<sup>3+</sup> ions 4f→5d (310–430 nm) change significantly, showing a double-peak characteristic. When the concentration of K<sup>+</sup> ions is 0.5, the absorption peak from the matrix disappears, which may be due to the phase transition of the matrix lattice caused by excessive K<sup>+</sup> ions or the introduction of a large number of defect energy levels into the matrix lattice. Moreover, K<sup>+</sup> ion doping can regulate the density and distribution of traps. TL curves show that a small quantity of K<sup>+</sup> doping increases the trap density of shallow traps. When a large quantity of K<sup>+</sup> is doped, the phase changes of matrix lattice and the defect density decrease. Secondly, the doping of Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> matrix by different luminescent centers (Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup>) is studied. The results show that the multicolor luminescence emission in red, blue and green bands and the tunable multimode luminescence (up/down conversion luminescence, afterglow luminescence and photo-stimulated luminescence) are realized by the selective excitation. According to the multicolor and multimode characteristics of the phosphors, a butterfly-shaped anti-counterfeiting pattern is designed. Owing to the different energy level positions of the luminescence centers, dynamic multicolor photoluminescence is realized by selective excitation at different wavelengths. Based on the upconversion luminescence characteristics of Er<sup>3+</sup> and the excellent afterglow characteristics of Pr<sup>3+</sup> in Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> material, the designed anti-counterfeiting pattern shows the dynamic color change and multicolor, multimode high-order anti-counterfeiting application.

Blue-light-excitable pure and efficient short-wave infrared luminescenceviaCr3+→ Yb3+energy transfer in a KYbP2O7:Cr3+phosphor

A novel KYbP2O7:Cr3+inorganic phosphor that emits pure and efficient SWIR photoluminescence upon blue light excitation has been developed, and can be used as a stable luminescence converter for a SWIR emitter.

Based on triphenylamine-imidazole skeleton electrofluorochromic small organic molecules: Synthesis and electrofluorochromic properties

Five donor–acceptor (D-A) small organic molecule compounds were designed and synthesized by using triphenylamine (TPA) as the donor and imidazole as the acceptor. Through introducing different substituent groups at the para position of TPA, the excited state characteristics were adjusted, and a reversible and stable color change was obtained. These compounds exhibited good thermal properties. All five compounds were evaluated as small organic molecule materials for electrofluorochromism (EFC) and achieved luminescence conversion from blue to yellow at low voltages, and the compound 4e realized electroluminescence conversion at only 0.6 V due to the introduction of –OCH3. The stability of the EFC devices was demonstrated by the CV curves for 400 cycles. The color-changing voltages of EFC can be effectively reduced by adjusting the characteristics of ICT. This rational structural design of small organic molecules provides a new design strategy for the preparation of EFC materials.

Enhancement of the frequency conversion film imaging effect based on a cascade material fusion method.

Frequency conversion imaging technology can provide an effective way for infrared detection against the limitations of conventional infrared detectors, such as expense and cooling requirements, but the converted luminescence intensity of frequency conversion materials limits the application of this technology. In this paper, a cascade material (CM) fusion method is proposed to improve the conversion luminous intensity and thus enhance the frequency conversion imaging effect at 1550 nm near infrared (NIR) excitation. First, we derived from the energy level transition mechanism of CM that the CM fusion method can achieve three excitations of substrate materials (SMs). It can improve the conversion luminescence intensity of SM in CM. Then, we experimentally prepared CM and SM films and simultaneously measured the frequency conversion imaging effect of the two films at 1550 nm NIR excitation. It was found that the weight ratio of doped material (DM) to SM affects the imaging enhancement of CM films. Therefore, we compared the imaging grayscale value intensity of CM films with different weight ratios under the same detection conditions. Finally, it was concluded that the best enhancement of frequency conversion imaging was achieved with a DM to SM weight ratio of 0.25 for this mechanism. The enhancement was about 3.11 times compared to SM films.

Near-infrared quantum cutting in NaYF4:Ce3+,Yb3+ nanocrystals for luminescent solar concentrators

A series of Ce3+-Yb3+ ions codoped NaYF4 nanocrystals were prepared by hydrothermal method. The structure, morphologies, photoluminescence properties and fluorescence dynamics were studied systemically. In Ce3+-Yb3+ ions codoped NaYF4 nanocrystals, strong near-infrared (NIR) emission at 900–1100 nm was observed under the excitation of 5d level of Ce3+ ions. The lifetime of Ce3+ ions decreased increases with increasing Yb3+ ions concentration. The back energy transfer from Yb3+ ions to Ce3+ ions in NaYF4 nanocrystals does not occur. As a near-infrared luminescent convertor, the kinds of materials have potential to be applied in luminescent solar concentrators (LSCs) and efficient NIR emitters.

PH-responsive hybrid materials with dynamic photoluminescence for anti-counterfeiting, encryption and biogenic amines detection

Thanks to the superior performance and convenience for preparation and operation, programmable memory materials have drawn extensive attention as the ever-higher requirements for anti-counterfeiting. In this work, a lanthanide-doped pH-responsive luminescent sensor (MMT@[Eu(Phen)2]-PFX, MMT = montmorillonite, PFX = pefloxacin) was prepared to achieve reversible multicolor luminescence conversion (from blue to red) by changing the pH of the solution, and thus brought about the designation of a portable test strip for biogenic amines detection. Moreover, multiple encryption and decryption of confidential information can be materialized by combining the sensor with digital code and Morse code. Additionally, the optical memory device MMT@ [Eu(Phen)2]-PFX@CS (CS = chitosan) enabled reversible switching of sol-gel and emission colors synchronously during acid-base conversion. Hence, this smart fluorescent material can be widely applied in the fields of information security and biogenic amines detection for the future.

In-situ oriented Sc-Co3O4 nanowire arrays for highly efficient ethanol detection

Improving the response of gas sensors has always been a hot research topic. Due to their unique electronic energy level structure, the compositing rare-earth (RE) element materials display unique properties in many fields such as catalysis, luminescence, and energy conversion. Along these lines, combining materials with the RE element of scandium (Sc) is considered a new method to optimize the performance of sensors based on the employment of ZIF-67 derived Co3O4 nanowire arrays. In this work, the Sc element was uniformly distributed on the surface of the Co3O4 nanowires, which were grown by enforcing hydrothermal and chemical bath-based methods. Based on the 30 % Sc composite Co3O4 nanowire array, the sensors show a maximum response of 32–100 ppm ethanol at a lower operating temperature (110 °C). The variation of the response was small range even after 35 days. Interestingly, the extracted response has increased more than three times that of the pure Co3O4 nanowire array devices. In addition, we tested the ethanol concentration range of 10–500 ppm and showed good performance. The gas-sensing properties of the sensors were systematically tested towards volatile organic compounds, including ethanol, acetone, methanol, etc. Based on the 30 % Sc composite Co3O4 nanowire array, the sensors still exhibit excellent selectivity to ethanol. The enhanced sensing performance is attributed to the strong catalytic effect of Sc and the modification of the surface morphology of Co3O4 by Sc. Our work provides an effective and promising method for improving the ethanol sensing performance of the ZIF-67 derived Co3O4 nanowires at low-temperature values.

An excitation wavelength-dependent color-tunable La4GeO8: Bi3+, Er3+ phosphor for multicolor anticounterfeiting

Stimulation-responsive luminescent materials have attractd intense attention due to their excellent optical properties in the anticounterfeiting application. At present, most the anticounterfeiting materials are based on single luminescence and fixed excitation patterns, resulting in a poor anticounterfeiting effect. Therefore, developing multimodal anticounterfeiting materials that change their luminous color under different wavelength stimuli has become a significant challenge. In this work, we reported a multimodal luminescent La 4 GeO 8 : Bi 3+ , Er 3+ phosphor, which could emit white, blue-green, baby blue and orange-yellow light at the excitation wavelength of 250–430 nm. Moreover, it also showed green upconversion (UC) luminescence when irradiated with near-infrared (NIR, 980 nm and 808 nm) lasers. Notably, the material exhibited good humidity resistance and stability. Based on these integrated features, we designed an anticounterfeiting device. The results suggested that the anticounterfeiting device could quickly realize multimodal anticounterfeiting using common light source {NIR (808 nm or 980 nm) laser and ultraviolet (UV) lamp}. These combined characteristics will be difficulty to forge and show high security in anticounterfeiting applications. A multimodal luminescent La 4 GeO 8 : Bi 3+ , Er 3+ phosphor • An advanced tunable multimodal luminescent La4GeO8: Bi3 + , Er3 + is developed. • The material could tune colors from white, blue-green, baby blue and orange yellow light under the increased excitation wavelength from 250 nm to 420 nm. • The phosphor also realizes successfully up conversion luminescence under the NIR (980 nm and 808 nm) laser irradiation. • The anticounterfeiting devices was easily detected by using a portable ultraviolet lamp or NIR (808 nm or 980 nm) laser and it was impossible to counterfeit by any substitute so far, which provided a high level of security.

State Filling and Stimulated Emission by Colloidal InP/ZnSe Core/Shell Quantum Dots

AbstractColloidal InP‐based quantum dots (QDs) are widely studied for luminescent color conversion or electroluminescence, yet the nature of the emitting state remains a matter of debate and reports on stimulated emission by these materials are nearly absent. Here, the properties of photo‐excited InP/ZnSe QDs are investigated using femtosecond transient absorption spectroscopy. It is shown that the evolution of the band‐edge bleach with increasing exciton number can be interpreted as state filling of the conduction‐ and valence‐band edge states by delocalized electrons and holes. In line with this interpretation, net stimulated emission is observed once the average exciton number exceeds 1. The authors account for this lower‐than‐expected gain threshold and the spectral properties of the gain band by reckoning that the Stokes shift between band‐edge absorption and emission is the dominant spectral shift. The underlying exciton–phonon coupling leads to a stimulated emission mechanism, where also single excitons can lead to net optical gain. To fully profit from this advantageous stimulated emission scheme, it is argued that InP/ZnSe QDs with more narrow emission lines are needed and spurious trapping of electron–hole pairs at high exciton numbers must be suppressed, for example, by better controlling the composition of the core/shell interface.

Full-Spectrum InP-Based Quantum Dots with Near-Unity Photoluminescence Quantum Efficiency

Photoluminescent color conversion by quantum dots (QDs) makes possible the formation of spectrum-on-demand light sources by combining blue LEDs with the light generated by a specific blend of QDs. Such applications, however, require a near-unity photoluminescence quantum efficiency since self-absorption magnifies disproportionally the impact of photon losses on the overall conversion efficiency. Here, we present a synthesis protocol for forming InP-based QDs with +90% quantum efficiency across the full visible spectrum from blue/cyan to red. The central features of our approach are as follows: (1) the formation of InP core QDs through one-batch-one-size reactions based on aminophosphine as the phosphorus precursor, (2) the introduction of a core/shell/shell InP/Zn(Se,S)/ZnS structure, and (3) the use of specific interfacial treatments, most notably the saturation of the ZnSe surface with zinc acetate prior to ZnS shell growth. Moreover, we adapted the composition of the Zn(Se,S) inner shell to attain the intended emission color while minimizing line broadening induced by the InP/ZnS lattice mismatch. The protocol is established by analysis of the QD composition and structure using multiple techniques, including solid-state nuclear magnetic resonance spectroscopy and Raman spectroscopy, and verified for reproducibility by having different researchers execute the same protocol. The realization of full-spectrum, +90% quantum efficiency will strongly facilitate research into light-matter interaction in general and luminescent color conversion in particular through InP-based QDs.

Solar-absorbing energy storage materials demonstrating superior solar-thermal conversion and solar-persistent luminescence conversion towards building thermal management and passive illumination

Nowadays, building energy consumption accounts for more than 50% of the total energy consumption. Exploiting advanced solar energy strategy is of great significance to achieve the building energy saving by spontaneously providing energy for a building. Herein, novel solar-absorbing energy storage materials constructed by solar-thermal conversion material, phase change material gel and persistent luminescence material are proposed to efficiently utilize the full spectrum of renewable solar energy towards the building thermal management and passive illumination. A flow chemical synthesis strategy is designed to continuously prepare the solar-thermal conversion material N, S-co-doped conjugated polybenzobisthiazole towards the robust solar energy harvesting (solar absorbance of 94.1%) and considerable thermal energy production (solar-thermal conversion efficiency of 88.3%). The liquid phase blending and sol–gel transition are proposed to fabricate the phase change material gels demonstrating high latent heat of 192.12 Jg−1 and self-supporting capacity, which can store the heat generated by N, S-co-doped conjugated polybenzobisthiazole and release the heat in the night. The persistent luminescence materials can absorb the ultraviolet–visible light in the solar spectrum in the daytime and emit the multicolour luminescence in the night. Taking advantages of the synergistic effect of the functional components, the proposed solar-absorbing energy storage materials demonstrate full spectrum utilization of solar energy (total solar absorbance of 91.93%) towards the building thermal management and passive illumination with a solar-light conversion efficiency of 1.65% and a solar-thermal conversion efficiency of 10.52%. The solar-absorbing energy storage materials create a state-of-the-art alternative for the next-generation energy saving buildings.

Upconversion photoluminescence and radiative properties of Ba2CaWO6: Er3+ phosphors for photonic applications

Trivalent erbium doped Ba2CaWO6 phosphors were synthesized by the solid-state reaction method. Nephelauxetic ratio and bonding parameter were calculated from the absorption spectrum in order to understand the nature of Er3+ ion-ligand bonds in the prepared phosphor samples. The phenomenological Judd-Ofelt (JO) analysis has been implemented to the recorded absorption spectrum of Ba2CaWO6: Er3+ phosphors for evaluating the JO parameters. Under 980 nm laser diode excitation, Ba2CaWO6: Er3+ phosphor exhibits strong green (4S3/2 →4I15/2) and weak red (4F9/2 →4I15/2) upconversion (UC) emissions centered at 566 and 680 nm and an intense downconversion NIR emission at 1.5 μm. The UC process were assessed on the basis of power dependence of upconversion emission intensity. The significant luminescence features observed from the photoluminescence spectra of Ba2CaWO6: Er3+ phosphors that comprise of both up conversion and down conversion luminescence were discussed in detail with the aid of partial energy level diagram. The better values of radiative properties, luminescence features and CIE color coordinates suggest the suitability of Er3+ doped Ba2CaWO6 material for various photonic applications.

Thermoinduced structural-transformation and luminescent conversion in hybrid manganese halides

We report here the synthesis of hybrid manganese halide crystals, (C4H7N2)MnCl3 · H2O and (C4H7N2)2MnCl4, by using the same organic ligand 2-methylimidazole. Upon heating treatment, the red-emissive (C4H7N2)MnCl3 · H2O crystal is structurally transformed into green-emissive (C4H7N2)2MnCl4 crystal in situ. The crystal structural analysis reveals that the [MnCl5 · H2O]3− octahedra chains decompose into mono [MnCl4]2− tetrahedra, accompanied by the departure of H2O molecules. Upon cooling in air or water vapor, the crystal structure and luminescence of (C4H7N2)2MnCl4 are transformed to those of (C4H7N2)MnCl3 · H2O. The in situ conversion of luminescence between (C4H7N2)MnCl3 · H2O and (C4H7N2)2MnCl4 provides new insight into the potential application of hybrid manganese halides.

Characterization of Luminescent Down-Shifting Spectral Conversion Effects on Silicon Solar Cells with Various Combinations of Eu-Doped Phosphors.

Luminescent down-shifting (LDS) spectral conversion is a feasible approach to enhancing the short-wavelength response of single junction solar cells. This paper presents the optical and electrical characteristics of LDS spectral conversion layers containing a single species or two species of Eu-doped phosphors applied to the front surface of silicon solar cells via spin-on coating. The chemical composition, surface morphology, and fluorescence emission of the LDS layers were respectively characterized using energy-dispersive X-ray analysis, optical imaging, and photoluminescence measurements. We also examined the LDS effects of various phosphors on silicon solar cells in terms of optical reflectance and external quantum efficiency. Finally, we examined the LDS effects of the phosphors on photovoltaic performance by measuring photovoltaic current density–voltage characteristics using an air-mass 1.5 global solar simulator. Compared to the control cell, the application of a single phosphor enhanced efficiency by 17.39% (from 11.14% to 13.07%), whereas the application of two different phosphors enhanced efficiency by 31.63% (from 11.14% to 14.66%).

Spectrally tunable and thermally stable near-infrared luminescence in Na3Sc2(PO4)3:Cr3+ phosphors by Ga3+ co-doping for light-emitting diodes

Tunable and thermally stable NIR photoluminescence has been realized in Na3Sc2(PO4)3:Cr3+ phosphors by co-doping Ga3+ ions. Their application as a luminescence converter for NIR LEDs is also demonstrated.

A tricolor-switchable stimuli-responsive luminescent binuclear Cu(i) complex with switchable NH⋯O interactions

Blue-green-yellow tricolor luminescence conversion is attributed to the loss and recovery of CH2Cl2 solvent molecules and the destruction and restoration of the orderly packing array caused by the breaking and rebuilding of NH⋯O hydrogen bonds.

Dye-Sensitized Rare Earth Nanoparticles with Up/Down Conversion Luminescence for On-Demand Gas Therapy of Glioblastoma Guided by NIR-II Fluorescence Imaging.

As the primary malignant tumor in the brain, glioblastoma exhibits a high mortality due to the challenges for complete treatment by conventional therapeutic methods. It is of great importance to develop innovative therapeutic agents and methods for treatment of glioblastoma. In this work, the imaging and therapy of glioblastoma are reported by using dye sensitized core-shell NaYF4 :Yb/Tm@NaYF4 :Nd nanoparticles with strong up/down-conversion luminescence, of which the ultraviolet up-conversion emissions at 348 and 365nm are significantly enhanced by nearly 28 times and used to control the release of SO2 from 5-Amino-1,3-dihydrobenzo[c]thiophene 2,2-dioxide prodrug for gas therapy, and the second near-infrared (NIR-II) down conversion emission at 1340nm is increased five times and applied for imaging. It is revealed that the released SO2 molecules not only cause oxidative stress damage of tumor cells, but also induce their pro-death autophagy by down-regulating the expression of p62 and up-regulating the ratio of LC3-II/LC3-I, ultimately inhibiting tumor growth. The work demonstrates the great potential of rare earth nano-platform with functions of NIR-II imaging and photo-controlled gas therapy in the diagnosis and treatment of orthotopic glioblastoma.