Two-Dimensional-Layered Perovskite ALaTa2O7:Bi3+ (A = K and Na) Phosphors with Versatile Structures and Tunable Photoluminescence

Preparation and Luminescence Properties of Broadband Orange-Emitting Persistent ScBaZn3GaO7:Bi3+ Phosphor

This article describes a new kind of afterglow material, ScBaZn3GaO7:Bi3+, which was synthesized through a high-temperature solid-phase method. Its crystal structure, photoluminescent characteristics, and afterglow characteristics were studied and analyzed. Upon excitation at 344 nm, ScBaZn3GaO7:Bi3+ exhibits broadband emission with a central wavelength located at 571 nm (fwhm = 172.98 nm). The sample exhibits an internal quantum efficiency of 65.1%. The bright yellow persistent luminescence of the ScBaZn3GaO7:Bi3+ sample was observed after 365 nm irradiation. Thermoluminescence spectroscopy revealed four primary traps within ScBaZn3GaO7:Bi3+, with depths of 0.676, 0.794, 0.882, and 0.972 eV. The traps located at energy levels of 0.676 and 0.794 eV were identified as the key contributors to the sample's afterglow. Finally, the ScBaZn3GaO7:Bi3+ sample was combined with a UV-LED chip to fabricate a high-power warm white-light-emitting diode (WLED) device, indicating the potential application prospect of ScBaZn3GaO7:Bi3+ phosphor in single-phase warm WLEDs.

Bright white light emission from lanthanide oxide LaGdO3 for LED lighting by Bi3+ to Eu3+ energy transfer

Phosphors with intrinsic white light emission are of great potential in constructing high-quality white LEDs (WLEDs). In this work, we propose the use of energy transfer from Bi3+ to Eu3+ ions for white light emission. A unique Bi3+-activated phosphor LaGdO3 (LGO):Bi3+ was generated using the conventional high-temperature solid-state process. An energy transfer was established by introducing Eu3+ into the phosphor composition. The emission colour of LGO:Bi3+,Eu3+ phosphors changes from cyan to white to orange-red depending on the Bi3+/Eu3+ doping proportion. The energy transfer between the Bi3+ and Eu3+ ions results from the dipole-dipole interaction. The LGO:Bi3+,Eu3+ phosphors were combined with a near-ultraviolet chip to successfully create a single-component WLED device with a colour-rendering index of 92.4. Our work demonstrates the energy transfer as a route for single-component white light emission and makes LGO:Bi3+,Eu3+ phosphors one of the candidate materials for near-ultraviolet lighting.

Layered Perovskites BaLnnInnO3n+1 (n = 1, 2) for Electrochemical Applications: A Mini Review

Modern humanity is facing many challenges, such as declining reserves of fossil energy resources and their increasing prices, climate change and an increase in the number of respiratory diseases including COVID-19. This causes an urgent need to create advanced energy materials and technologies to support the sustainable development of renewable energy systems including hydrogen energy. Layered perovskites have many attractions due to their physical and chemical properties. The structure of such compounds contains perovskite layers divided by layers with different frameworks, which provide their properties' features. Proton-conduction layered perovskites open up a novel structural class of protonic conductors, potentially suitable for application in such hydrogen energy devices as protonic ceramic electrolysis cells and protonic ceramic fuel cells. In this mini review, the special features of proton transport in the novel class of proton conductors BaLn_nIn_nO_3n+1 (n = 1, 2) with a layered perovskite structure are observed and general regularities are discussed.

Local structure and ionic transport in acceptor-doped layered perovskite BaLa2In2O7

Materials with perovskite or perovskite-related structure have many applications because of theirs different physical and chemical properties. These applications are extremely diverse and cover different fields including hydrogen energy. Layered perovskites with Ruddlesden-Popper structure constitute a novel class of ionic conductors. In this paper, the effect of acceptor doping on the local structure and its relationship with transport properties were shown for layered perovskites based on BaLa2In2O7 for the first time. The geometric factor (the increase in the unit cell volume due to the increase in the ionic radii of cations) plays major role in the area of small dopant concentration (x  0.15). The concentration factor (the increase in the oxygen vacancy concentration) is more significant in the area of big dopant concentration (x  0.15). The acceptor doping is a promising way of improving the oxygen-ionic conductivity of layered perovskite BaLa2In2O7.

Oxygen Ion and Proton Transport in Alkali-Earth Doped Layered Perovskites Based on BaLa2In2O7

Inorganic materials with layered perovskite structures have a wide range of physical and chemical properties. Layered perovskites based on BaLanInnO3n+1 (n = 1, 2) were recently investigated as protonic conductors. This work focused on the oxygen ion and proton transport (ionic conductivity and mobility) in alkali-earth (Sr2+, Ba2+)-doped layered perovskites based on BaLa2In2O7. It is shown that in the dry air conditions, the nature of conductivity is mixed oxygen–hole, despite the dopant nature. Doping leads to the increase in the conductivity values by up to ~1.5 orders of magnitude. The most proton-conductive BaLa1.7Ba0.3In2O6.85 and BaLa1.7Sr0.15In2O6.925 samples are characterized by the conductivity values 1.2·10−4 S/cm and 0.7·10−4 S/cm at 500 °C under wet air, respectively. The layered perovskites with Ruddlesden-Popper structure, containing two layers of perovskite blocks, are the prospective proton-conducting materials and further material science searches among this class of materials is relevant.

Tb3+/Sm3+ co-doped double perovskite: synthesis, exfoliation and luminescence properties

Tb³⁺/Sm³⁺ co-doped double perovskite K[K_1.5(Tb_1-xSm_x)_0.5]Ta₃O₁₀ (denoted as KKT_1-xS_xTO) was prepared, which exhibited typical Tb³⁺ and Sm³⁺ photoluminescence emissions and tunable colours. After protonation and subsequent exfoliation processes, unilaminar KT_1-xS_xTO nanosheets with a lateral size of ∼300 nm and thickness of ∼2.7 nm were obtained.

Bi3+ and Sm3+ co-doped Cs2AgInCl6 perovskite microcrystals with co-enhancement of fluorescence emission

Bi3+–Sm3+ co-doped Cs2AgInCl6 MCs show a combination of luminescence in the visible range.

Visible-light excited polar Dion-Jacobson Rb(Bi1-xEux)2Ti2NbO10 perovskite: Photoluminescence properties and in-vitro bioimaging

Rare-earth ion-activated oxide phosphors are beneficial to overcome the problems like photobleaching, reduced lifetime, and the blinking of organic dyes and quantum dots for bioimaging applications. In this work, we...

Doping Pb2+ in LaAlO3 to generate dual emission centers and an optical storage container for visible and near infrared persistent luminescence

Defects play an important role in luminescence, not only as non-radiative transition centers to decrease the luminescence intensity, but also as useful centers for improving luminescence. Phosphors with unique characteristics can be designed by using effective defects combined with the luminescence center. Here, a novel phosphor of LaAlO₃:Pb²⁺ was synthesized by a solid state reaction. Two kinds of defects, which are and Pb'_La, were constructed by incorporation of Pb²⁺ into LaAlO₃. Under UV excitation at 285 nm, the sample outputted a broad cyan emission at 460 nm that is related to the ³P₁-¹S₀ transition of Pb²⁺, along with a weak near infrared (NIR) emission at 735 nm. However, only NIR emission at 735 nm can be found upon 211 nm excitation. The defect levels of and Pb'_La in the band gap are evidenced to be the contributor for the NIR output. Heating the sample resulted in a weakened cyan emission and an enhanced NIR output. Because the defects of and Pb'_La also act as the electron and hole traps, the sample outputted cyan and NIR afterglows after removing the irradiation source. Since the optical signal of LaAlO₃:Pb²⁺ is sensitive to the excitation wavelength, temperature, and duration time, the multimodal luminescent phosphor may be used as a potential anti-counterfeiting material.

Vibrational and optical studies of a nonlinear optical crystal, Cs2Bi2O(Ge2O7)

Single crystals of a non-centrosymmetric and polar Cs₂Bi₂O(Ge₂O₇) compound were grown from melt. This material was characterized by polarized Raman scattering at room temperature. The comparison to the polycrystalline IR and Raman spectra has been made and assignment of all observed modes to the respective vibrations and their symmetry has been proposed. Our results show that this crystal is promising SRS-active nonlinear optical material for up- and down-Raman laser-frequency converters with the most intense lasing line at 481 cm^-1. Optical studies show that Cs₂Bi₂O(Ge₂O₇) exhibits intense absorption bands with peaks maxima at 260 and 293 nm (77 K) typical for ¹S₀→^1,3P₁ transitions of Bi³⁺ ions, which are parity-allowed due to spin-orbit coupling as well as unexpected band centered at 360 nm that was assigned to intervalence charge transfer transition.

Cr,Yb-codoped Ca2LaHf2Al3O12 garnet phosphor: electronic structure, broadband NIR emission and energy transfer properties

The combination of a broadband near-infrared (NIR) phosphor and phosphor-converted light-emitting diodes (pc-LEDs) has proven to be an ideal choice for a high-efficiency NIR light source. Here, a garnet-type NIR Ca₂LaHf₂Al₃O₁₂:Cr³⁺ phosphor is obtained and its emission covered most of the NIR spectral range. Excited by 460 nm blue light, the maximum peak was located at 780 nm with a full width at half maximum (FWHM) of ∼141 nm and an internal quantum efficiency (IQE) of 33%. Moreover, the NIR spectra can be broadened by doping Yb³⁺ into the Ca₂LaHf₂Al₃O₁₂:Cr³⁺ garnet phosphor. A super broad FWHM of 300 nm and reduced thermal quenching were acquired, originating from the energy transfer of Cr³⁺→ Yb³⁺. The energy transfer process of Cr³⁺ and Yb³⁺ is described by means of an energy level diagram and time-resolved spectrum. Finally, a NIR pc-LED is fabricated by combining the Ca₂LaHf₂Al₃O₁₂:Cr³⁺,Yb³⁺ phosphor with blue chips, which has a photoelectric conversion efficiency of 10%. These results demonstrate the great potential of Ca₂LaHf₂Al₃O₁₂:Cr³⁺,Yb³⁺ in super broadband NIR pc-LED applications.

Recent Advances in Super Broad Infrared Luminescence Bismuth-Doped Crystals

Bismuth (Bi)-doped materials are capable of exhibiting broadband near-infrared (NIR) luminescence in 1,000-1,700 nm; driven by the potential use in lasers and broadband optical amplifiers for modern fiber communication systems, Bi-activated NIR luminescencent glasses and related devices have attracted much attention. Compared with glass systems, Bi-doped crystals as gain media usually have more regular crystal structures to produce stronger NIR signals, and developing such materials is highly desirable. Regarding the recent advances in Bi-doped NIR crystals, here, for the first time, we summarized such crystals listed as two main categories of halogen and oxide compounds. Then, by comparing the substitution site, coordination environment, emission and excitation luminescence peaks, emitting center species, and decay times of these known Bibased NIR crystals, discussion on how to design Bi-doped NIR crystals is included. Finally, the key challenges and perspectives of Bi-doped NIR crystals are also presented. It is hoped that this review could offer inspiration for the further development of Bi-doped NIR luminescent crystals and exploit its potential applications.

Ultraviolet-A Persistent Luminescence of a Bi3+-Activated LiScGeO4 Material

Long persistent phosphors (LPPs) with ultraviolet (UV) luminescence have great potential for application in the fields of biomedicine, environmental, and catalysis. However, it is currently limited by the design and development of remarkable UV LPPs with a suitable spectral region and an ultralong afterglow decay time. Herein, we develop a new type of Bi³⁺-activated LiScGeO₄ LPP, which exhibits bright ultraviolet-A (UVA) persistent luminescence (PersL). Because of the existence of numerous stabilized effective traps, the as-synthesized phosphors can undergo an ultralong PersL decay time far longer than 12 h. The PersL properties, effective trap depths, distributions, and types, as well as the possible mechanism for the PersL behavior of LiScGeO₄:Bi³⁺, are comprehensively surveyed utilizing PersL excitation spectra, PersL decay analyses, thermoluminescence experiments, and X-ray photoelectron spectroscopy. This work can cover the shortage of LPPs in the UV region and also can lay the foundation for the development of more excellent UV LPPs toward versatile novel applications.

Photoluminescence control and abnormal Eu3+ orange emission in Ln3+ (Ln3+ = Ce3+, Eu3+)-doped oxyapatite-type phosphors

Controllable photoluminescence adjustment of Ce³⁺/Eu³⁺-doped phosphors.

Sb3+ Doping-Induced Triplet Self-Trapped Excitons Emission in Lead-Free Cs2SnCl6 Nanocrystals

Doped halide perovskite nanocrystals (NCs) have opened new opportunities for the emerging optical and optoelectronic applications. Here, we describe a hot-injection synthesis of all-inorganic lead-free Cs₂SnCl₆ and Sb³⁺ doped Cs₂SnCl₆ NCs. Cs₂SnCl₆ NCs present a blue emission peak at 438 nm, whereas a new broad-band emission peak appears at 615 nm for the Sb³⁺ doped NCs. Comparative structural and spectral characterizations of Sb³⁺ doped Cs₂SnCl₆ NCs with micrometer-sized undoped and Sb³⁺ doped crystals show that the formation of broad-band orange emission is originted from triplet self-trapped excitons, attributed to the ³P_n-¹S₀ transitions (n = 0, 1, 2). Our results in Sb³⁺ doped Cs₂SnCl₆ materials provide insights into the machanisms of doping-induced emission centers, and it extends the existing knowledge of optical properties of doped halide NCs for further studies.

Highly bright multicolor-tunable KSrLu(PO4)2:Ce3+, Tb3+, Mn2+ phosphors via efficient energy transfer

Research hotspots about Ce³⁺-Tb³⁺ and Ce³⁺-Mn²⁺ codoped multicolor-tunable materials, has grown rapidly and is still growing. However, few feasible strategies can be employed to achieve the multicolor-tunable luminescence under the premise of maintaining high QE. In this paper, KSrLu(PO₄)₂:0.25Ce presents a high luminescence efficiency with approximately 78% quantum efficiency. Furthermore, Ce³⁺-Tb³⁺ and Ce³⁺-Mn²⁺ codoped optimal samples give a green and red luminescence, which corresponds to a high 61% and 55% quantum efficiency due to a high energy transfer efficiency of Ce³⁺→Tb³⁺ and Ce³⁺→Mn²⁺. Besides, we achieved the precise adjustment of blue, green, orange and pink emissions of KSrLu(PO₄)₂:Ce³⁺, Tb³⁺, Mn²⁺ samples. Meanwhile, KSrLu(PO₄)₂:Ce³⁺, Tb³⁺ and KSrLu(PO₄)₂:Ce³⁺, Mn²⁺ phosphors present a weak thermal quenching: their integrated emission intensity at 500K still keep more than 80% of their initial intensity at room temperature. Therefore, the results might provide a novel multicolor-tunable phosphor for backlight display application.

Tailored Synthesis of an Unprecedented Pb-Mn Heterometallic Halide Hybrid with Enhanced Emission

Organic-inorganic lead halide hybrids have attracted extensive interest in solid-state lighting, due to their superior color tunability and low-cost solution processing. However, the relatively low photoluminescence quantum efficiency (PLQE) is a common issue for most bulk lead halide hybrids. Inspired by the intriguing luminescence properties of heterometallic complexes, we rationally developed an unprecedented two-dimensional (2D) Pb-Mn heterometallic halide hybrid, (C₅H₁₄N₂)₂Pb₄MnCl₁₄ (2), through a precisely tailored synthetic approach based on (C₅H₁₄N₂)₂Pb₅Cl₁₄ (1). Intriguingly, 2 features a unique 2D heterometallic halide layer configuration, in which the strong quantum confinement facilitates efficient energy transfer from bound excitons to d-states of Mn²⁺, resulting in highly sensitized Mn²⁺emission. The PLQE of 2 is up to 32%, considerably higher than that of pristine 1 (less than 1%). Moreover, 2 presents significant environmental and thermal stability, benefiting from its cluster feature. To our best knowledge, this is the first example of construction of a Pb-Mn heterometallic halide hybrid with bulk highly efficient red emission. This work provides a way to enhance the PLQE of lead halide hybrids via sensitization in rationally designed heterometallic halide hybrids.

New strategy for designing orangish-red-emitting phosphor via oxygen-vacancy-induced electronic localization

Phosphor-converted white-light-emitting diodes (pc-WLED) have been extensively employed as solid-state lighting sources, which have a very important role in people's daily lives. However, due to the scarcity of the red component, it is difficult to realize warm white light efficiently. Hence, red-emitting phosphors are urgently required for improving the illumination quality. In this work, we develop a novel orangish-red La₄GeO₈:Bi³⁺ phosphor, the emission peak of which is located at 600 nm under near-ultraviolet (n-UV) light excitation. The full width at half maximum (fwhm) is 103 nm, the internal quantum efficiency (IQE) exceeds 88%, and the external quantum efficiency (EQE) is 69%. According to Rietveld refinement analysis and density functional theory (DFT) calculations, Bi³⁺ ions randomly occupy all La sites in orthorhombic La₄GeO₈. Importantly, the oxygen-vacancy-induced electronic localization around the Bi³⁺ ions is the main reason for the highly efficient orangish-red luminescence. These results provide a new perspective and insight from the local electron structure for designing inorganic phosphor materials that realize the unique luminescence performance of Bi³⁺ ions.

Mn4+-activated BaLaMgSbO6 double-perovskite phosphor: a novel high-efficiency far-red-emitting luminescent material for indoor plant growth lighting

In this paper, we reported on Mn⁴⁺-activated BaLaMgSbO₆ double-perovskite phosphors showing efficient far-red emissions for plant growth applications.

Luminescent perovskites: recent advances in theory and experiments

This review summarizes previous research on luminescent perovskites, including oxides and halides, with different structural dimensionality. The relationship between the crystal structure, electronic structure and properties is discussed in detail.

Functional layered materials with heavy metal lone pair cations, Pb2+, Bi3+, and Te4+

Syntheses, structures, representative properties, and the structure–property relationships for a series of functional layered materials are presented.