Enhancement of Upconversion Luminescence through Three-Dimensional Design of Plasma Ti3O5-Coupled Structural Domain-Limiting Effects.

Upconversion luminescence plays a crucial role in various technological applications, and among the various valence states of lanthanide elements, Ln3+ has the highest stability. The 4f orbitals of these elements are in a fully empty, semifull, or full state. This special 4f electron configuration allows them to exhibit rich discrete energy levels. However, the 4f-4f transition of Ln3+ rare earth ions itself is prohibited, resulting in a lower luminescence efficiency. This limitation greatly hinders the practical application of upconversion luminescence. In this study, we report nanostructured luminescence-enhanced substrate platforms with both semiconductive local surface plasmons and spatially confined domain effects on a single defect semiconductor substrate. By coupling NaYF4:Yb-Er nanoparticle emitters to the surface of Ti3O5 NC-arrays plasmonic nanostructures, an ultrabright luminescence with a 32-fold increase in green emission and a 40-fold increase in red emission was achieved. Furthermore, the fluorescence resonance energy transfer characteristics observed in the R6G/NaYF4/Ti3O5 NC-array composite film enable accurate detection of fluorescent molecules. The results provide an innovative and intelligent approach to enhance the upconversion luminescence intensity of rare-doped nanoparticles and develop highly sensitive molecular detection systems based on the above luminescence enhancement.

The effect of MnCO3 on the gain coefficient for the 4I13/2 → 4I15/2 transition of Er3+ ions and near-infrared emission bandwidth flatness of Er3+/Tm3+/Yb3+ co-doped barium zinc silicate glasses.

The roles of Mn2+ ions in the MnCO3 compound, leading to the formation of an Mn2+-Yb3+ dimer and affecting the gain coefficient for the 4I13/2 → 4I15/2 transition of Er3+ ions and near-infrared (NIR) emission bandwidth flatness of Er3+/Tm3+/Yb3+ co-doped in SiO2-ZnO-BaO (SZB) barium zinc silicate glasses, were investigated in this work. The composition of all elements from the original raw materials that exist in the host glasses was determined using energy-dispersive X-ray spectroscopy (EDS). Under the excitation of a 980 nm laser diode (LD), the NIR emission of Er3+/Tm3+/Yb3+-co-doped SZB glasses produced a bandwidth of about 430 nm covering the O, E, and C bands. The effects of Mn2+ ions and the Mn2+-Yb3+ dimer on the gain coefficient for the 4I13/2 → 4I15/2 transition of Er3+ ions and bandwidth flatness of NIR emission of Er3+/Tm3+-co-doped and Er3+/Tm3+/Yb3+-co-doped SZB glasses were also assigned. The optimal molar concentration of Mn2+ ions was determined such that the NIR bandwidth flatness of Er3+/Tm3+/Yb3+-co-doped SZB glasses was the flattest. In addition, the role of Mn2+ ions in reducing the gain coefficient for the 4I13/2 → 4I15/2 transition of Er3+ ions was also calculated and discussed.

Engineering CsPbX3 (X = Cl, Br, I) Quantum Dot-Embedded Borosilicate Glass through Self-Crystallization Facilitated by NaF as a Phosphor for Full-Color Illumination and Laser-Driven Projection Displays.

All inorganic perovskite (CsPbX3, X = Cl, Br, I) quantum dot (QD) glass samples are considered the next generation of lighting materials for their excellent luminescence properties and stability, but crystallization conditions are difficult to control, which often leads to the inhomogeneous crystallinity of QDs. Here, we provided evidence that the presence of sodium fluoride induced self-crystallization of CsPbBr3 QDs during routine glass formation without the need for additional heat treatment. We showed that NaF simultaneously affected the network structure of glass and promoted the formation of CsPbBr3 QDs, that is, Na+ ions entered the glass network skeleton, partially interrupting the network structure, while the strong electronegativity of F- ions attracted Cs+ and Pb2+ ions into the gaps formed in the glass networks that had been loosened up by Na+ ions, which reduced the activation energy of crystallization processes. Our results showed that NaF-induced CsPbBr3 QDs glass had excellent thermal stability, high photoluminescence quantum efficiency (49%), and luminescent stability under high-power laser irradiation. Finally, this work also demonstrated the general applicability of this method in the making of a series of CsPbX3 (X = Cl, Br, I) QD glass samples by NaF-induced self-crystallization, which drastically expanded the color gamut to a range of full spectrum for luminescence and laser-driven projection displays. We believe that the work presented here represents a new direction for the research and development of full-color gamut inorganic perovskite quantum dot glass samples, which could have a significant impact on the future applications of laser-driven projection displays as well.

Optical band gaps and spectroscopy properties of Bi m+/Eu n+/Yb3+ co-doped (m = 0, 2, 3; and n = 2, 3) zinc calcium silicate glasses.

In this study, the indirect/direct optical band gaps and spectroscopy properties of Bi m+/Eu n+/Yb3+ co-doped (m = 0, 2, 3; and n = 2, 3) zinc calcium silicate glasses under different excitation wavelengths were investigated. Zinc calcium silicate glasses with the main compositions of SiO2-ZnO-CaF2-LaF3-TiO2 were prepared by the conventional melting method. EDS analysis was performed to determine the elemental composition existing in the zinc calcium silicate glasses. Visible (VIS)-, upconversion (UC)-, and near-infrared (NIR)-emission spectra of Bi m+/Eu n+/Yb3+ co-doped glasses were also investigated. Indirect optical band gaps and direct optical band gaps of Bi m+-, Eu n+- single-doped, and Bi m+-Eu n+ co-doped SiO2-ZnO-CaF2-LaF3-TiO2-Bi2O3-EuF3-YbF3 zinc calcium silicate glasses were calculated and analyzed. CIE 1931(x, y) color coordinates for VIS and UC emission spectra of Bi m+/Eu n+/Yb3+ co-doped glasses were determined. Besides, the mechanism of VIS-, UC-, NIR-emissions, and energy transfer (ET) processes between Bi m+ and Eu n+ ions were also proposed and discussed.

Lead-Free Double Perovskite Cs2NaErCl6: Li+ as High-Stability Anodes for Li-Ion Batteries.

Halide perovskite materials have been used in the field of lithium-ion batteries because of their excellent ion migration characteristics and defect tolerance. However, the current lead-based perovskites used for lithium-ion batteries are highly toxic, which may hinder the pace of further commercialization. Therefore, it is still necessary to develop a new type of stable and pollution-free perovskite anode material. Herein, we for the first time use a high-concentration lithium-ion doped rare-earth-based double perovskite Cs2NaErCl6:Li+ as the negative electrode material for a lithium-ion battery. Thanks to its excellent structure stability, the assembled battery also has high cycle stability, with a specific capacity of 120 mAh g-1 at 300 mA g-1 after 500 cycles with a Coulomb efficiency of nearly 100%. The introduction of a rare earth element in a lead-free double perovskite paves a new way for the development of novel promising anode materials in the field of lithium storage applications.

All-Inorganic Lead Free Double Perovskite Li-Battery Anode Material Hosting High Li+ Ion Concentrations.

Perovskite materials, as a multifunctional material, have been widely applied in the field of electrochemistry due to its ion migration properties. Although the lead based halide perovskite has been applied in the anode of the lithium battery, it is necessary to develop new lead-free perovskite anode materials because of its the instability and environmental unfriendliness. Herein, we develop a facile grinding method to prepare ultrahigh Li+ concentration doping Cs2NaBiCl6 powders, which are used as the anode material of the lithium battery. The assembled battery possesses a stable specific capacity of about 300 mA h g-1 with over 99% Coulombic efficiency. Owing to their particular crystal structure with high adjustability, the double perovskite materials have promising potentials in lithium storage applications.

Influences of copper-potassium ion exchange process on the optical bandgaps and spectroscopic properties of Cr3+/Yb3+ co-doped in lanthanum aluminosilicate glasses.

In this study, lanthanum aluminosilicate glasses with compositions of 45SiO2-20Al2O3-12.5LaF3-10BaF2-9K2O-1Cr2O3-2.5Yb2O3 (SALBK) were prepared using the conventional melting method and copper-potassium ion exchange process. Influences of the ion exchange process between copper and potassium on the visible, upconversion, and near-infrared luminescence spectra of Cr3+/Yb3+ co-doped under excitations of 343, 490, and 980 nm LD were investigated. The EDS analysis of SALBK glasses was measured to confirm the presence of atoms in the glasses. The values of direct and indirect bandgaps of Cr3+/Yb3+ co-doped SALBK glasses were calculated and analyzed. Besides, the energy exchange processes between Cu+, Cu2+ ions, and Cr3+, Yb3+ ions were also proposed and discussed.

High-Stable X-ray Imaging from All-Inorganic Perovskite Nanocrystals under a High Dose Radiation.

All-inorganic perovskites of CsPbBr3 nanocrystals (NCs) exhibit strong X-ray absorption and have been demonstrated to be highly efficient scintillators for X-ray detection and imaging. However, the long-term stability of the perovskite remains a major hurdle in practical applications, especially under a commercial dose of X-ray irradiation (0.5-5.5 mGy·s-1). Herein, with a solution-protected annealing approach reconstructing the CsPbBr3 NCs free from undesired defects, the perovskite scintillators provide a long-term (∼3600 s) stable visualization tool for X-ray radiography (1.44 × 106 captured images for the exposure time of 2.5 ms per image) under the irradiation dose of 1 mGy·s-1. This work opens a window for the stability of perovskite scintillators and demonstrates their robust and long-term efficient radioluminescence (RL) for low-cost radiography and X-ray imaging application.

Atomic-Scale Insights into the Dynamics of Growth and Degradation of All-Inorganic Perovskite Nanocrystals.

An understanding of growth and degradation pathways is significant to solve the problem of the structural instability of all-inorganic perovskite nanocrystals (NCs). However, it is still a great challenge to directly record such dynamic processes with high spatial resolution owing to the existence of complex internal factors even using in situ transmission electron microscopy observation. Here, we employ a glassy matrix to produce CsPbBr3 NCs to ensure that the growth and degradation processes of CsPbBr3 NCs are recorded in the vacuum chamber, which could avoid the influence of the external factors, under electron beam (E-beam) irradiation. In addition, two stages of degradation pathways induced by the E-beam are observed sequentially: (1) a layer-by-layer decomposition and (2) instantaneous vanishing once the radius reaches the critical radius (∼2.3 nm). Indeed, we demonstrated that defects serve as a key flash point that could trigger the structural collapse of CsPbBr3 NCs. Our findings provide critical insights into the general instability issue of all-inorganic perovskite NCs in practical applications.

The synthesis of a perovskite CsPbBr3 quantum dot superlattice in borosilicate glass.

For the first-time we have synthesised perovskite CsPbBr3 quantum dot (QD) superlattices in borosilicate glass, which play a key role in controllable network structure connectivity. The structural and optical properties of the CsPbBr3 QD superlattices embedded in borosilicate glass were investigated.

Evaluation of particle penetration factors based on indoor PM2.5 removal by an air cleaner.

The particle penetration factor is an important parameter to determine the concentration of indoor particles. In this paper, a mathematical model for calculating this parameter was established by combining with the decay of the indoor PM2.5 and CO2 concentrations measured in a bedroom with an air cleaner. The convergence of the penetration factors was analyzed under different working conditions. The results show that the particle penetration factors converge to stable values within the range of 0.69 to 0.84 close to the value from the empirical formula when the indoor PM2.5 concentration decays to stable values. When the role of particle deposition is ignored, the penetration factors at the low and middle airflow modes are 0.78 and 0.69, respectively. The particle penetration factors are mainly determined by the clean air delivery rate (CADR) of the air cleaner, clearance airflow, and I/O ratio during the balanced phase when the roles of indoor particle deposition and exfiltration can be ignored. This work can provide a convenient method for the calculation of the particle penetration factor.

Novel organic-inorganic hybrid powder SrGa12O19:Mn2+-ethyl cellulose for efficient latent fingerprint recognition via time-gated fluorescence.

Latent fingerprints (LFPs) are important evidence in crime scenes and forensic investigations, but they are invisible to the naked eye. In this work, a novel fluorescent probe was developed by integrating a narrow-band-emitting green afterglow phosphor, SrGa12O19:Mn2+ (SGO:Mn), and ethyl cellulose (EC) for the efficient visualization of LFPs. The hydrophobic interactions between the powder and lipid-rich LFPs made the ridge structures more defined and easily identifiable. The background fluorescence of the substrates was completely avoided because of the time-gated fluorescence of the afterglow phosphor. All the three levels of LFP degrees were clearly imaged due to the high sensitivity. Moreover, the SGO:Mn-EC powder was highly stable in neutral, acidic, and alkaline environments. In addition, 60 day-aged LFPs were successfully visualized by the powder. All performances showed that this strategy for LFP recognition has merits such as low cost, non-destructive nature, reliability, superior universality, and legible details. Together, these results show the great application prospects of this powder in forensic identification and criminal investigation.

Ultrahigh photo-stable all-inorganic perovskite nanocrystals and their robust random lasing.

Photo-instability has prevented further commercialization of all-inorganic perovskite nanocrystals (NCs) in the field of high-power optoelectronics. Here, an accelerated transformation process from non-luminescent Cs4PbBr6 to CsPbBr3 NCs with bright green emission is explored with irradiation at 365 nm during water-triggered structural transformation. The photoelectric field provided by the photon energy of 365 nm promotes the rapid stripping of CsBr and atomic reconstruction, contributing to the production of ultrahigh photo-stable defect-free CsPbBr3 NCs. The robust emission output of the as-obtained CsPbBr3 NCs is well preserved even when recorded after 160 min. Moreover, a long-term stable random lasing could be achieved when excited using an ∼800 nm femtosecond laser for at least 8.6 × 107 laser shots. Our results not only elucidate the photo-induced accelerated phase transformation process of the all-inorganic perovskites, but also open up opportunities to synthesize highly stable CsPbBr3 NCs for their practical application in photovoltaics and optoelectronics.

Extrinsic photoluminescence properties of individual micro-particle of Cs4PbBr6 perovskite with "defect" structure.

Optical performance of the lead halide perovskites with zero-dimension (0D) structure has been in a hot debate for optoelectronic applications. Here, Cs4PbBr6 hexagonal micro-particles with a remarkable green emission are first fabricated via a low-temperature solution-process employed ethanol as solvent. Our results underline that the existence of bromine vacancies and the introduction of hydroxyl induce a narrowed band gap with the formation of a defect level, which contributes to the extrinsic photoluminescence (PL) properties synergistically. Thanks to the high exciton binding energy and the unique morphology with a regular geometric structure of the as-obtained micro-particles, two-photon pumped amplified spontaneous emission (ASE) and single mode lasing from an individual Cs4PbBr6 particle are realized. Our results not only provide an insight into the origin of optical emission from Cs4PbBr6, but also demonstrate that the versatile Cs4PbBr6 offers a new opportunity for novel nonlinear photonics applications as an up-conversion laser.

Modified surface states of NaGdF4:Yb3+/Tm3+ up-conversion nanoparticles via a post-chemical annealing process.

An amorphous layer acting as a quenching center at the surface of oleic acid-capped NaGdF4:Yb3+/Tm3+ nanoparticles is observed directly, which can be reconstructed via a novel post-chemical annealing process. The amorphous phase of the surface layer of NaGdF4:Yb3+/Tm3+ nanoparticles gradually crystallizes as the post-chemical annealing temperature increases; meanwhile, the good dispersibility of the as-obtained nanoparticles is maintained. The reduction of surface defects and higher local symmetry of the crystal field environment around the doped rare-earth ions contribute to drastically increased up-conversion (UC) emission intensity of the NaGdF4:Yb3+/Tm3+ nanoparticles. In particular, the blue emission of Tm3+ at 450 nm enhances 10-fold after the post-chemical annealing process at 250 °C compared with the counterpart without further surface-state treatments. The color gamut of well-crystallized NaGdF4:Yb3+/Tm3+ with a modified surface covers the blue to yellow region in CIE chromaticity coordinates via a non-steady-state UC process. The results indicate that the surface states of these UC nanoparticles can be feasibly improved via the post-chemical annealing process without encouraging agglomeration, which further optimizes their UC properties for practical applications.

Phase transformation induced reversible modulation of upconversion luminescence of WO3:Yb3+, Er3+ phosphor for switching devices.

The upconverting luminescence properties of phosphors are dependent on the hosts. In this work, the WO3:Yb3+, Er3+ phosphor was prepared, and the reversible phase transformation from the WO3 to the WO2 was obtained by alternating the sintering in a reducing atmosphere or in air. The influence of reversible phase transformation on the upconversion luminescence was investigated first. The WO3:Yb3+, Er3+ phosphor exhibits the visible upconversion luminescence, while no upconversion luminescence was observed in the WO2:Yb3+, Er3+ phosphor. The reversible modulation of upconversion luminescence of the WO3:Yb3+, Er3+ phosphor retains the excellent reproducibility, exhibiting the potential applications in data storage and optical switches.

Rb+ cations enable the change of luminescence properties in perovskite (RbxCs1-xPbBr3) quantum dots.

All-inorganic metal halide perovskites of the formulation ABX3 (where A is Cs+, B is commonly Pb2+, and X is a halide, X = Cl, Br, I) have been studied intensively for their unique properties. Most of the current studies focus on halogen exchange to modify the luminescence band gap. Herein we demonstrate a new avenue for changing the band gap of halide perovskites by designing mixed-monovalent cation perovskite-based colloidal quantum dot materials. We have synthesized monodisperse colloidal quantum dots of all-inorganic rubidium-cesium lead halide perovskites (APbBr3, A = mixed monovalent cation systems Rb/Cs) using inexpensive commercial precursors. Through the compositional modulation, the band gap and emission spectra are readily tunable over the visible spectral range of 474-532 nm. The photoluminescence (PL) of RbxCs1-xPbBr3 nanocrystals is characterized with excellent (NTCS color standard) wide color gamut coverage, which is similar to the cesium lead halide perovskites (CsPbX3, X = mixed halide systems Cl/Br), and narrow emission line-widths of 27-34 nm. Furthermore, simulated lattice models and band structures are used to explain the band gap variations.

Adjustable multicolor up-energy conversion in light-luminesce in Tb3+/Tm3+/Yb3+ co-doped oxyfluorifFde glass-ceramics containing Ba2LaF7 nanocrystals.

Transparent oxyfluoride glasses with highly efficient up-energy conversion (UEC) luminescence were developed in the 45SiO2-15Al2O3-12Na2CO3-21BaF2-7LaF3-xTbF3-yTmF3-zYbF3 composition (in mol%), and structural investigation by X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of face-centered cubic Ba2LaF7 nanocrystals. The colors of UEC luminescences could be tuned easily by adjusting the concentration of doped rare earth ions and the excitation power of laser simultaneously. The relationship between the emission intensity of Tb3+/Tm3+/Yb3+ co-doped oxyfluoride glass-ceramics and the excitation pump power revealed that three-photon and two-photon absorptions predominated in the conversion process from the infrared into blue and red luminescences, respectively. A novel UEC mechanism of red emission from Tm3+ was proposed, energy transfers from Yb3+ to Tm3+ and Tb3+ and from Tm3+ to Tb3+ were evidenced. The possible mechanism responsible for the color variation of UEC in Tb3+/Tm3+/Yb3+ co-doped was discussed.

Color Tunable and Upconversion Luminescence in Yb-Tm Co-Doped Yttrium Phosphate Inverse Opal Photonic Crystals.

For this paper, YPO4: Tm, Yb inverse opals with the photonic band gaps at 475 nm and 655 nm were prepared by polystyrene colloidal crystal templates. We investigated the influence of photonic band gaps on the Tm-Yb upconversion emission which was in the YPO4: Tm Yb inverse opal photonic crystals. Comparing with the reference sample, significant suppression of both the blue and red upconversion luminescence of Tm3+ ions were observed in the inverse opals. The color purity of the blue emission was improved in the inverse opal by the suppression of red upconversion emission. Additionally, mechanism of upconversion emission in the inverse opal was discussed. We believe that the present work will be valuable for not only the foundational study of upconversion emission modification but also the development of new optical devices in upconversion lighting and display.

Upconversion Luminescence Properties of NaYF4 Nanocrystals Precipitated Nd3+/Nb3+/Ho3+ Tri-Doped Oxyfluoride Glass Ceramics.

Transparent oxyflouride glass ceramics composed of SiO2-Al2O3-Na2O-NaF-YF3 tri-coped with Nd3+/Yb3+/Ho3+ were prepared by thermal treatment. Segregation of NaYF4 nanocrystals in the matrix was confirmed from structural analysis by means of X-ray diffraction and transmission electron microscopy. Compared with glass samples, very strong green upconversion (UC) luminescence due to the Ho3+: (4F5, 5S2) --> 51(8) transition was observed in the glass ceramics under 808 nm excitation. It was found that upconversion intensity of Ho3+ strongly depends on the Nd3+ concentration, and the energy transfer process from Nd3+ to Ho3+ via Yb3+ was proposed.