Search

In the last five years, significant progress has been achieved in incorporating trivalent lanthanide (Ln3+) ions into CsPbX3 halide perovskite nanocrystals (PeNCs), combining superior optoelectronic performance of semiconductors with abundant Ln3+: 4f–4f transitions. However, doping divalent europium (Eu2+) with parity-allowed 5d–4f transition inside CsPbX3 remains unexplored. Herein, we develop a new class of dual-emitters based on Eu2+-doped CsPbCl3 PeNCs. Narrowband violet emission and broadband orange emission assigned to the respective exciton recombination and Eu2+: 5d → 4f transition are concurrently observed. Steady/transient-state photoluminescence (PL) spectra, time-resolved PL (TRPL) spectra and femtosecond transient absorption (fs-TA) spectra evidence independent dual-emissions without exciton-to-Eu2+ energy transfer, which is attributed to the preferred location of Eu2+ on the surface of CsPbCl3. As a consequence, exciton-longitudinal optical phonon interplay and surface ligand–Eu2+ coupling in the as-prepared Eu:CsPbCl3 PeNCs are verified based on temperature-sensitive spectroscopic analyses, together with first-principles density functional theory (DFT) calculations and crystal-field calculations. These findings provide fundamental insights into the design of novel lanthanide-doped halide perovskite emitters for versatile optoelectronic applications. [ABSTRACT FROM AUTHOR]

Perovskite quantum dots are considered to be one of the most promising materials for next-generation backlight displays due to their narrow emission width, high color purity and tunable luminescence. However, the deterioration and failure of perovskite quantum dots under stimulation from the external environment (e.g., light, heat, and humid air) limit their practical applications. Herein, CsPbBr3@glass with excellent stability and optical properties was successfully prepared by optimizing the quantum dot nucleation/growth conditions. The CsPbBr3@glass@PDMS hierarchical structure film with a full width at half maximum of ∼17 nm and photoluminescence quantum yield of ∼80% was obtained via the physical dilution method to eliminate the internal filtering effect. Benefiting from the dual protection of the inorganic glass network and PDMS polymer matrix, the film exhibited excellent water/heat resistance. As an application demonstration, a white LED backlit unit was designed by coupling a CsPbBr3@glass@PDMS green film and Mn4+:K2SiF6 red film with a home-made blue light guide panel, endowing the LCD with a wide color gamut (a color gamut of 159% for commercial LCD, 108% for NTSC, and 81% for Rec. 2020), confirming its great potential in the display industry. [ABSTRACT FROM AUTHOR]

The development of luminescent materials with concurrent tunable spectral profile and brightness is a great challenge to improve the security of the authentic items and shield against counterfeiting. Herein, we report the realization of in situ hexagonal-to-cubic phase transition of Yb/Er:NaLuF4 nanocrystals inside inorganic glass via simply modifying the heating (glass crystallization) temperature, leading to simultaneous control of upconversion emission color and intensity. Impressively, this peculiar phase transition process is reversible upon cyclic heating/cooling thermal-treatment and the accompanying repeatable upconversion emission behaviors are retained. It is experimentally demonstrated that multiple patterns visualized using screen-printing inks containing the investigated samples and the anti-counterfeiting prototypes are practically applicable by switching in situ glass crystallization temperatures. These findings show great promise of the designed lanthanide-doped NaLuF4@glass nanocomposites in high-level anticounterfeiting applications and give new insights for the development of advanced optical materials. [ABSTRACT FROM AUTHOR]

In situ nanocrystallization of homogeneously distributed Lu–Ln (Lu = La–Lu, Sc) solid-solution potassium lanthanide fluorides inside the same aluminosilicate glass matrix is reported. These precipitated nanocrystals exhibit Ln3+ radius dependent phase structures, i.e., cubic K(Lu/Ln)3F10 for large-radius Ln3+ ions and orthorhombic K(Lu/Ln)2F7 for small-radius Ln3+ ones. Particularly, a Lu–Yb system shows the ability to completely substitute between Lu and Yb in the K(Lu/Yb)2F7 nanocrystals, and Er (2 mol%):K(Lu0.5Yb0.5)2F7@glass yields the best upconversion quantum yield of 0.7%, which is far higher that the value of well-known Yb/Er (20/2 mol%):NaYF4@glass (0.13%). Taking Er/Tm:K(Lu0.5Yb0.5)2F7@glass as a color converter, a 980 nm laser-driven upconverted lighting device can be constructed to produce bright white-lighting with an optimal luminous efficiency of 0.53 lm W−1 and an energy efficiency of 1.31%. In addition, Er:KYb2F7@glass shows a significant photothermal effect owing to 100% Yb3+ host ions, leading to 980 nm laser-power-sensitive upconversion luminescence colors. As a proof-of-concept experiment, a specially designed Er:KYb2F7@glass-based flower pattern with tunable upconversion colors is adopted to demonstrate its practical application in high-end anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Laser lighting, generally consisting of a blue laser and downconversion phosphors, is considered to be the next promising form of illumination to replace traditional LED lighting. However, irradiation with a high-powered blue laser will inevitably cause significant thermal attack, which places a high demand on phosphor converters as well as on device architecture. In this work, a proof-of-concept prototype of near-infrared laser-driven upconversion solid-state-lighting is proposed. Robust lanthanide doped α/β-NaYF4 embedded glass ceramics are developed as upconverted color converters and a routine 980 nm laser is used as the pumping source for its relatively low thermal effect and perfect resonance with Yb3+ sensitizers. Stable and bright upconversion white light is indeed produced by coupling a Yb/Tm/Er doped α-NaYF4 glass ceramic with a 980 nm laser, but the luminous efficiency and energy efficiency are only 0.3 lm W−1 and 0.12%, respectively, owing to low Er doping concentration. As an alternative, a stacking structure of Yb/Tm doped and Yb/Er doped glass ceramics is designed as a color converter to improve the luminous efficiency up to 1.0 lm W−1 and energy efficiency up to 0.5% under a laser power density of 275 W cm−2. It is believed that this research will provide a new idea for laser lighting and open up the application field of glass ceramics. [ABSTRACT FROM AUTHOR]

In the past few years, metal halide perovskite quantum dots and nanocrystals have been extensively explored due to their unique optoelectronic properties and extensive application prospects. In this review article, we provide an overview of the synthesis, microstructure variation, luminescence properties and potential applications of hybrid organic–inorganic perovskites and all-inorganic perovskites. Firstly, several widely used wet chemical methods for synthesizing perovskite quantum dots are summarized, and then the related structures and morphologies of different perovskites as well as the relationship between the microstructure and optical properties are given. Additionally, correlative metal halides with B-site ion replacement or doping and some strategies to improve the stability of perovskite materials are highlighted. Subsequently, a brief introduction about their potential applications in light-emitting diodes, photodetectors and lasing is presented. Finally, some conclusions and outlooks will be introduced. It is expected that this review article will provide valuable insights into the current status of perovskite luminescent materials and stimulate new ideas and further research on their practical applications. [ABSTRACT FROM AUTHOR]

Efficient dual-modal luminescence is highly desired for applications in high security anti-counterfeiting. In the present work, Yb3+/Ln3+/Mn4+ (Ln = Er, Ho, and Tm) tri-doped Na3ZrF7 phosphors were fabricated via oil–water interface cation exchange using Yb3+/Ln3+:Na3ZrF7 as the exchanging hosts. The as-prepared products exhibited typical Mn4+ red down-shifting luminescence under UV light excitation and Er3+ red, Ho3+ yellow and Tm3+ near-infrared multi-color upconversion emissions under 980 nm laser excitation. The Mn4+ dopants in the Na3ZrF7 host experienced strong crystal-field strength Dq of 3.63 and showed superior thermal stability with up to 90% of the initial emission intensity retained at 448 K. Steady-state and time-resolved emission spectra verified that there was no detrimental energy transfer interaction between Mn4+ and Ln3+, enabling bright and eye-visible bi-functional emissions for the present products. As a consequence, the as-prepared phosphors were demonstrated to be applicable in anti-counterfeiting by a proof of concept experiment of fluorescent labeling for specially designed patterns. [ABSTRACT FROM AUTHOR]

Nowadays, Mn4+-doped red phosphors are widely used in white LEDs to improve the color rendering index and decrease the correlated color temperature. Great efforts have been made to enhance the luminous efficiency. In this work, new composite particles containing two fluorides with similar structures K2LiAlF6 and K2NaAlF6 were developed to improve the emission intensity. The composite particles contain K2LiAlF6 and K2NaAlF6 phases with an increase of Na content. The particle sizes of the products were in the nanoscale and the element distribution was investigated. Importantly, the as-prepared composite particles had higher emission intensity than simple mixtures. Structural and optical characterization studies were systematically carried out to understand the enhancement mechanism. Finally, a white LED device was fabricated by combining the synthesized red phosphor and YAG:Ce on a blue chip. [ABSTRACT FROM AUTHOR]

Phosphor-in-glass (PiG), which serves as both a luminescent convertor and organic encapsulation material in high-power white light-emitting diodes (w-LEDs), has become a prospective research hotspot owing to its high transparency and thermal stability. However, YAG:Ce3+ PiG-based LED devices still suffer from a lack of a red component. Therefore, the development of red phosphors with excellent quantum efficiency and superior thermal stability is urgent. Herein, a highly efficient La2Li1−ySb1−xO6:xMn4+,yMg2+ red phosphor with a broadband emission ranging from 670 to 720 nm was fabricated via a conventional solid-state reaction. By co-doping Mg2+ in La2LiSbO6:Mn4+, the emission intensity was enhanced significantly, which reaches as high as 10 times that of the single-doped La2LiSbO6:Mn4+. It is proposed that the Mg2+ dopant can compensate imbalanced charges for the substitution of Sb5+ by Mn4+ and interrupt adverse energy transfer among the Mn4+ activators. Impressively, a maximum quantum yield of up to 80.3% is achieved and about 80% emission intensity is retained at the temperature of 423 K. Furthermore, the crystal field strength (Dq) and Racah parameters (B and C) together with the nephelauxetic ratio (β1) were calculated based on the obtained spectroscopic data. By embedding the red-emitting La2LiSbO6:Mn4+,Mg2+ phosphor and yellow-emitting YAG:Ce3+ phosphor into TeO2-based glass, an inorganic PiG composite as a color converter to replace organic silicone was acquired. The excellent optical parameters and tunable chromaticity feature of the fabricated w-LEDs were achieved by adjusting the mass ratio of La2LiSbO6:Mn4+,Mg2+ to YAG:Ce3+ in the PiG plate, where the correlated color temperature changed from cool white (6555 K) to warm (4130 K) and the color rendering index increased from 73.7 to 86.6 under an operating current of 300 mA. [ABSTRACT FROM AUTHOR]

Currently, all inorganic perovskite quantum dots (QDs) of cesium lead halides (CsPbX3, X = Cl, Br, and I) have been mainly fabricated using wet chemical methods. Unfortunately, applications of perovskite QDs have been limited due to their poor stability. In the present work, the in situ growth of whole-family CsPbX3 (X = Cl, Br, and I) perovskite QDs in Zn–P–B–Sb based oxide glass via a glass crystallization strategy is reported. The as-prepared CsPbX3 QDs@glass nanocomposites exhibit typical excitonic recombination emissions and superior chemical stability benefited from the protection of the robust inorganic glass matrix. Through modifying the molar ratio of halide sources in glass, multi-color tunable emissions in the entire visible spectral range of 400–750 nm are achieved. As a result, light-emitting diode devices can be constructed by coupling blue-emissive CsPbBrCl2, green-emissive CsPbBr3 and red-emissive CsPbBr0.5I2.5 QDs@glass powders with a commercial ultraviolet chip, yielding bright white light luminescence with excellent optoelectronic performance. [ABSTRACT FROM AUTHOR]

This work demonstrates a novel mechanism of temperature sensitive upconversion luminescence. The Yb/Er:La2MoO6 phosphor is taken as a typical example. The laminated lattice structure of the La2MoO6 host endows a high potential of the 4F7/2 + 4I11/2→4F9/2 + 4F9/2 cross relaxation of the Er3+ dopant. It is found that such cross relaxation is sensitive to the variation of temperature, resulting in a distinct variation in fluorescence intensity ratio and thus a remarkable thermochromic upconversion luminescence. Employing this material as an optical thermometer, the maximum relative sensitivity is calculated to be 1.6% K−1 at room temperature, which is superior to most of the Er based thermometers reported previously. In addition, when an impulse pump is utilized, the maximum sensitivity can be further enhanced up to 3.3% K−1. The anisotropic thermal expansion of the La2MoO6 host lattice is proposed to be responsible for such temperature dependent luminescence. Other hosts (i.e. LaOCl and BiOCl) with similar laminated lattice structures have also been investigated, which exhibit a similar temperature sensing property. This work not only presents a novel strategy for constructing upconversion thermometric materials, but also provides inspiration that developing impulse excited optical thermometric materials might be a promising route for the field of temperature sensing. [ABSTRACT FROM AUTHOR]

All inorganic CsPbX3 (X = Cl, Br, I) perovskite quantum dots have attracted extreme attention due to their excellent optical performance. Unfortunately, heavy usage of the toxic Pb element is still a serious problem that needs to be solved. In the present work, Mn-doped CsPbCl3 nanocrystals are successfully prepared via a facile solvothermal reaction for the first time. A high Cs-to-Pb feeding ratio is necessary to achieve pure cubic perovskite phase and the incorporation of Mn dopants into the CsPbCl3 host is highly related to the Mn-to-Pb feeding ratio. Importantly, it is demonstrated that Mn-doped CsPbCl3 NCs synthesized by the solvothermal method have better stability than those prepared by traditional hot injection. To finely adjust the bandgap of CsPbCl3 NCs, Cl-to-Br anion exchange is used to fabricate Mn-doped CsPb(Cl/Br)3 NCs with tunable multi-color luminescence. Finally, the as-prepared Mn-doped CsPb(Cl/Br)3 products are demonstrated to be applicable as color converters for constructing white light-emitting diodes and optical thermometric medium for accurate temperature sensing. [ABSTRACT FROM AUTHOR]

The preparation of CsPbX3 nanoplatelets and the investigation of their optical properties have been rarely reported. Herein, the successful development of all-inorganic CsPbX3 (X = Cl, Br, or I) perovskite quantum dots has been achieved and their unique optical and electrical properties are discussed. apre-dissolution assisted solvothermal reaction was developed to synthesize ultrathin (∼3 nm) CsPbBr3 nanoplatelets with strong exciton absorption, with a 0.41 eV blue-shifted emission relative to that of CsPbBr3 nanocrystals and a high quantum yield of 28%. Anion exchange allowed the variation of the halogen content of the nanoplatelets and allowed them to retain their shape and size and achieve multi-color emission. [ABSTRACT FROM AUTHOR]

Solar hydrogen generation via photocatalytic water splitting represents an attractive strategy to address the global energy crisis and environmental pollution issues. CdS-based photocatalysts, including nanosized CdS powder, CdS-based solid solutions and CdS quantum dots, have attracted significant attention for photocatalytic H2 production due to their unique advantages, including strong visible light absorption capacity, suitable band edge levels and excellent electronic charge transfer. This review focuses on recent advances in material design and technological aspects of CdS-based photocatalysts for applications in photocatalytic H2 production. A brief overview of basic concepts and principles of photocatalytic water splitting was given in the Introduction section, followed by the basic properties of CdS. Then, the utilization of three main types of CdS-based semiconductor photocatalysts for solar H2 generation is introduced, and those important factors which can determine the photocatalytic performance were also discussed in detail. Special consideration has been given to the effect of morphology, interfacial junctions, exposing facet and cocatalysts on the photocatalytic performance of CdS-based photocatalysts. Finally, a roadmap of possible future directions to further explore the research field of CdS-based photocatalysts for solar H2 generation is also discussed. [ABSTRACT FROM AUTHOR]

In this work, low-melting (700 °C) phosphosilicate glasses embedded with CsPbX3 (X = Br, I) perovskite quantum dots (QDs) were fabricated via a glass crystallization strategy. The as-prepared CsPbBr3 QDs@glass nanocomposites exhibited typical green luminescence assigned to exciton recombination radiation and outstanding thermal stability due to the protection of the robust inorganic glass host. Multi-color tunable emissions in the spectral range of 500–750 nm were achieved by modifying the molar ratio of halide sources in the glass. As a proof-of-concept experiment, a light-emitting diode device was constructed by coupling the green-emitting CsPbBr3 QDs@glass and red-emitting CsPbBr2I QDs@glass with a commercial InGaN blue chip, yielding a bright white light emission with excellent optoelectronic performance. It is expected that the investigated CsPbX3 QDs@glass nanocomposites may find promising application as color converters in solid-state-lighting. [ABSTRACT FROM AUTHOR]

With admirable luminescence performance and a cheap price, non-rare-earth-based oxide red phosphors are a potential competitor of rare-earth-doped phosphors for warm white LEDs (WLEDs). Herein, a novel double-perovskite Ba2GdSbO6:Mn4+ phosphor, demonstrating strong red emission ascribed to a spin-forbidden Mn4+:2Eg→4A2g transition in the region of 620–750 nm, has been synthesized via a solid-state reaction route. The microstructure and luminescence properties are investigated in detail. The concentration quenching mechanism and thermal stability based on thermal quenching characteristics are also discussed. Importantly, Li+, Mg2+, Zn2+, Si4+, Ti4+ and Ge4+ dopants are discovered to be beneficial for enhancing Mn4+ luminescence, and the related mechanisms are comprehensively described. In addition, by combining red-emitting Ba2GdSb0.994O6:0.003Mn4+,0.003Mg2+ with the commercial blue-emitting BaMgAl10O17:Eu2+ and green-emitting Ba3La6(SiO4)6:Eu2+ phosphors in various ratios, a series of WLED devices with a tunable correlated color temperature (CCT) evolving from 6256 to 3486 K and a color rendering index (CRI) increasing from 72.1 to 88.3 are achieved. [ABSTRACT FROM AUTHOR]

Successful development of all-inorganic CsPbX3 (X = Cl, Br, or I) perovskite quantum dots (PQDs) has been witnessed due to their unique optical and electrical properties. However, the heavy usage of Pb element in PQDs has limited the commercial application of these PQDs, and the preparation of low-Pb or Pb-free PQDs is imperative. In this study, we report room-temperature reverse synthesis of CsPbxMn1−xCl3 PDQs from CsMnCl3 precursor nanocrystals through cation exchange. Interestingly, two-step phase transformation processes from hexagonal CsMnCl3 to rhombohedral Cs4PbxMn1−xCl6 and finally to cubic CsPbxMn1−xCl3 are evidenced. With an increase in the reaction time, Mn2+ ions in the PQD lattice are gradually replaced by Pb2+ ions. Notably, Mn2+ d → d broadband luminescence is not detected for the Cs4PbxMn1−xCl6 product, but it is intense for the CsPbxMn1−xCl3 sample owing to efficient energy transfer from CsPbCl3 to Mn2+. Moreover, it is found that the introduction of Br− into the reaction system will prohibit the complete phase transformation from rhombohedral Cs4PbxMn1−x(Cl/Br)6 to cubic CsPbxMn1−x(Cl/Br)3. By controlling the ratio between the CsMnCl3 precursor and PbBr2, tunable luminescence is easily achieved due to the combined emissions from both CsPb(Cl/Br)3 PQDs and Mn2+-emitting centers. [ABSTRACT FROM AUTHOR]

It is common that thermal quenching in luminescent materials inevitably occurs with an elevation in temperature. Herein, an inverse thermal quenching effect in lanthanide-doped upconversion nanocrystals was reported. Specifically, defects with an appropriate energy state were designed in Yb/Er (Ho, Tm) doped Na3ZrF7 nanocrystals to actualize a thermal-induced enhancement in luminescent intensity. Owing to this special temperature dependent optical property, our results reveal that these kinds of materials are very suitable for high security anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

Owing to its low-cost and satisfactory luminescent-emission performance in warm white light-emitting diodes (w-LEDs), the non-rare-earth Mn4+-activated red phosphor has become a promising competitor of commercial rare-earth doped phosphor. In this study, a series of novel red-light emitting phosphors based on Ca2YSbO6:Mn4+ have been developed successfully by a conventional solid-state reaction. The structural and luminescent properties of these phosphors are systematically investigated. The as-prepared Ca2YSbO6:Mn4+ product exhibits a broad excitation band ranging from 250 to 600 nm and an abnormal intense deep-red emission centered at 680 nm with a full width at half maximum (FWHM) of ∼46 nm. The optimal Mn4+ doping concentration is about 0.3 mol%, and the concentration quenching mechanism is determined to be a dipole–dipole interaction. Impressively, the Ca2YSbO6:0.003Mn4+ phosphor shows an outstanding quantum efficiency of 62.6% and an excellent thermal stability. In addition, the effect of Li+, Mg2+, Na+ and K+ dopants on the luminescent properties of Mn4+-doped Ca2YSbO6 phosphors is elucidated. Furthermore, by employing the as-prepared Ca2YSbO6:Mn4+ as a red component, a warm w-LED with high color rendering index (Ra = 87.5) and low correlated color temperature (CCT = 3255 K) can be acquired. It is believed that the present phosphor has a potential application as a supplement of the red component for warm w-LEDs. [ABSTRACT FROM AUTHOR]

As a novel type of promising materials, metal halide perovskites are a rising star in the field of optoelectronics. On this basis, a new frontier of zero-dimensional perovskite-related Cs4PbBr6 with bright green emission and high stability has attracted an enormous amount of attention, even though its photoluminescence still requires to clarification. Herein, the controllable phase transformation between three-dimensional CsPbBr3 and zero-dimensional Cs4PbBr6 is easily achieved in a facile ligand-assisted supersaturated recrystallization synthesis procedure via tuning the amount of surfactants, and their unique optical properties are investigated and compared in detail. Both Cs4PbBr6 and CsPbBr3 produce remarkably intense green luminescence with quantum yields up to 45% and 80%, respectively; however, significantly different emitting behaviors are observed. The fluorescence lifetime of Cs4PbBr6 is much longer than that of CsPbBr3, and photo-blinking is easily detected in the Cs4PbBr6 product, proving that the zero-dimensional Cs4PbBr6 is indeed a highly luminescent perovskite-related material. Additionally, for the first time, tunable emissions over the visible-light spectral region are demonstrated to be achievable via halogen composition modulations in the Cs4PbX6 (X = Cl, Br, I) samples. Our study brings a simple method for the phase control of CsPbBr3/Cs4PbBr6 and demonstrates the intrinsic luminescence nature of the zero-dimensional perovskite-related Cs4PbX6 products. [ABSTRACT FROM AUTHOR]

Expanding the photoresponse range of TiO2-based photocatalysts is of great interest for photocatalytic H2 production. Herein, noble-metal-free CuInS2 quantum dots were employed as a novel inorganic dye to expand the visible light absorption of TiO2/MoS2 for solar H2 generation. The as-prepared CuInS2/TiO2/MoS2 photocatalysts exhibit broad absorption from the ultraviolet to near-infrared region. Under visible light irradiation (λ ＞ 420 nm), the CuInS2/TiO2/MoS2 photocatalyst with 0.6 mmol g−1 CuInS2 and 0.5 wt% MoS2 showed the highest H2 evolution rate with a value of 1034 μmol h−1 g−1. Moreover, a considerable H2 evolution rate of 141 μmol h−1 g−1 was obtained under the irradiation of the optimized CuInS2/TiO2/MoS2 photocatalyst with ＞500 nm light. The reaction mechanism of the CuInS2/TiO2/MoS2 photocatalyst for photocatalytic H2 evolution was investigated in detail by photoluminescence decay study, and the results showed that the photoexcited electrons of CuInS2 can be transferred efficiently through TiO2 to MoS2 and then react with the absorbed protons to generate H2. The reported sensitization strategy tremendously improves the visible light absorption capacity and the photocatalytic performance of TiO2-based photocatalysts. [ABSTRACT FROM AUTHOR]

Mn4+-Doped red fluoride phosphors have attracted significant interest of researchers because of their excellent luminescence properties that can address the issue of the lack of red light components in commercial white light-emitting-diodes (WLEDs). Herein, we synthesized two novel Mn4+-based phosphors based on two different K2LiAlF6 phases (cubic and trigonal). The quantum efficiency of cubic K2LiAlF6:Mn4+ was only 3.2%, but it underwent a dramatic increase to 87.5% when the trigonal phase changed to cubic K2LiAlF6. The trigonal phase was gradually transformed to the cubic phase by controlling the HF volume concentration; this led to an increase in the Mn content and enhancement of the emission intensity. The analysis of the experimental spectra of the synthesized phosphors was facilitated by the crystal field calculations of the K2LiAlF6:Mn4+ energy levels. A good agreement between the theoretical and experimental data was achieved. Special attention was paid to the structure of these two phases and the phase transition mechanism. The morphologies, compositions, and temperature-dependent photoluminescence properties were investigated in detail. The as-prepared phosphors showed excellent thermal and chromatic stabilities. Finally, the optimized K2LiAlF6:Mn4+ phosphor was blended with the YAG:Ce3+ yellow phosphor and a blue LED to fabricate WLEDs. The color rendering index (Ra) of this new WLED is 86, and the correlated color temperature (CCT) is 3498 K. These findings indicate that the K2LiAlF6:Mn4+ phosphor is a promising red phosphor for applications in WLEDs. [ABSTRACT FROM AUTHOR]

Bandgap-tunable black phosphorus quantum dots prepared by a liquid exfoliation method in a mixture solvent of N-methylpyrrolidone and oleic acid can act as efficient photocatalysts for the degradation of rhodamine B. This is the first report on solely black phosphorus capable of destroying organic pollutants under visible light irradiation. [ABSTRACT FROM AUTHOR]

Currently, efficient photon anti-Stokes (upconversion) luminescence is mostly limited to lanthanide (Ln3+) doped materials. There are a few reports on upconversion behaviors of transition-metal ions, whose (Stokes) emissions are known to be tunable by changing the crystal fields of the hosts. Herein, Yb/Ln/Cr (Ln = Er, Ho) tri-doped glass ceramics were fabricated by a melt-quenching route and subsequent glass crystallization, where Cr3+ dopants were evidenced to be incorporated into the precipitated LiGa5O8 nanocrystals and Ln3+ ions remained in the glass matrix. An intense Cr3+ upconversion luminescence assigned to the 2E →4A2 transition was observed upon 980 nm laser excitation via energy transfer from Yb3+ sensitizers to Er3+ activators/bridging-centers and finally to Cr3+ emitting centers. Importantly, the investigated glass ceramics presented temperature-dependent upconversion fluorescence intensity ratios for Er3+ 2H11/2/4S3/2 thermally coupled states as well as Cr3+/Ln3+ non-thermally coupled states and temperature-sensitive upconversion decays of Cr3+ 2E/4A2 thermally coupled states, enabling their promising applications in self-calibrated multi-modal temperature sensing. [ABSTRACT FROM AUTHOR]

In upconversion nanocrystals where Er3+ acts as the activator, concentration quenching will easily occur when the content of Er3+ is high (generally ＞5mol%), and the Er3+ spatial distribution which is a key factor affecting the concentration quenching is an important issue that must be considered. Herein, we selected Yb:NaErF4 as a light-emitting layer and investigated its upconversion performance and temperature sensing behaviors in two kinds of core–shell nanoarchitectures. Yb3+ and Er3+ activators were distributed in a three-dimensional sphere and two-dimensional thin layer in Yb:NaErF4@Yb/Nd:NaYF4@NaGdF4 and NaGdF4@Yb:NaErF4@Yb/Nd:NaYF4@NaGdF4 core–shell nanocrystals, respectively. The difference in Er3+ spatial distribution in the core–shell structure resulted in significant modification of red-to-green ratios and decay behaviors upon excitation at 376 nm, 808 nm, 980 nm and 1532 nm, and the related mechanisms were systematically investigated. In addition, the spatial distribution of Er3+ was demonstrated to have no obvious effect on the transitions of Er3+ thermally coupled 2H11/2→4I15/2 and 4S3/2→4I15/2 and the relative sensitivity for temperature determination under 808 nm laser excitation. [ABSTRACT FROM AUTHOR]

The development of (Bi0.5Na0.5)TiO3-based solid solutions with both high depolarization temperature Td and excellent piezoelectric and electromechanical properties for practical application is intractable because improved thermal stability is usually accompanied by a deterioration in piezoelectric and electromechanical performance. Herein, we report a 0–3 type 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 : 30 mol%ZnO composite (BNT-7BT : 0.3ZnO), in which the ZnO nanoparticles exist in two forms, to resolve the abovementioned long-standing obstacle. In this composite, Zn ions fill the boundaries of BNT-7BT grains, and residual Zn ions diffuse into the BNT-7BT lattice, as confirmed by XRD, Raman spectroscopy, and microstructure analysis. The BNT-7BT composite ceramics with a 0–3 type connectivity exhibited enhanced frequency-dependent electromechanical properties, fatigue characteristics, and thermal stabilities. More importantly, low poling field-driven large piezoelectric properties were observed for the composite ceramics as compared to the case of the pure BNT-7BT solid solution. A mechanism related to the ZnO-driven phase transition from the rhombohedral to tetragonal phase and built-in electric field to partially compensate the depolarization field was proposed to explain the achieved outstanding piezoelectric performance. This is the first time that the thermal stability, electromechanical behavior, and low poling field-driven high piezoelectric performance of BNT-based ceramics have been simultaneously optimized. Thus, our study provides a referential methodology to achieve novel piezoceramics with excellent piezoelectricity by composite engineering and opens up a new development window for the utilization of conventional BNT-based and other lead-free ceramics in practical applications. [ABSTRACT FROM AUTHOR]

Photocatalytic overall splitting of H2O into H2 and O2 using Z-scheme systems is a promising method for solar hydrogen generation. Most currently designed Z-scheme systems are usually based on precious metal cocatalyst modified semiconductor photocatalysts, thus exploiting noble-metal-free cocatalysts to replace precious metals is of huge interest. Herein, a noble-metal-free Z-scheme photocatalytic overall water splitting system was constructed by using MoS2/CdS as the H2 evolution photocatalyst, Co3O4/BiVO4 as the oxygen evolution photocatalyst and a [Co(bpy)3]3+/[Co(bpy)3]2+ redox couple as an electron mediator under visible light irradiation. It is found that the H2 and O2 evolution rates are approximate to an ideal ratio of 2 : 1, and the highest H2 and O2 evolution rates under visible light irradiation (λ ＞ 420 nm) are found to be 14.5 and 7.1 μmol h−1, respectively, with an excellent stability exceeding 12 h. The apparent quantum yield reaches up to 1.04% at wavelength λ = 420 nm even without any noble metal. The excellent stability and efficiency of this designed Z-scheme system in neutral water demonstrate its potential use for solar hydrogen generation. This work provides a noble-metal-free approach to construct the Z-scheme photocatalytic overall water splitting system. [ABSTRACT FROM AUTHOR]

Herein, hexagonal and cubic NaTbF4:Eu3+ nanocrystals embedded in transparent glass ceramics were successfully synthesized via a conventional melt-quenching technique followed by glass crystallization for the first time. Structural and spectroscopic characterizations evidenced the composition-dependent crystalline precipitation and the partition of Eu3+ dopants into the NaTbF4 host. In particular, the energy transfer mechanism from Tb3+ to Eu3+ was systematically investigated by photoluminescence spectra and decay curves, confirming that the energy transfer chain of Tb3+→ (Tb3+)n→ quenchers in NaTbF4 nanocrystals was replaced by Tb3+→ (Tb3+)n→ Eu3+ with the incorporation of Eu3+. The discrepant luminescence behaviors in terms of on-phase transformation were also studied. Furthermore, tunable emission could be achieved by merely adjusting the content of Eu3+, producing distinguishable emissions. As a consequence, it could be expected that NaTbF4:Eu3+ nanocrystals embedded in glass ceramics are promising candidates for applications in lightings and displays. [ABSTRACT FROM AUTHOR]

In the past few decades, efficient photon upconversion (anti-Stokes) luminescence has been extensively studied and is almost exclusively restricted to lanthanide (Ln3+) doped fluorophores. However, investigations on upconversion emissions of transition metal activators, whose (Stokes) luminescence is known to be tunable via modifying the crystal-field of the hosts, are extremely scarce. In the present work, a strategy to achieve Mn4+-based room-temperature near-infrared upconversion luminescence with the aid of efficient energy transfer of Yb3+→ Ln3+→ Mn4+ in specially prepared Yb3+/Ln3+/Mn4+ (Ln = Er, Ho, Tm):YAlO3 products is reported for the first time. Steady-state and time-resolved upconversion emission spectra are adopted to systematically clarify the related energy transfer mechanisms and determine energy transfer efficiencies. Benefitting from the completely different thermal-quenching mechanisms of Mn4+ and Ln3+ as well as the intermediate crystal field environment of Mn4+ in the YAlO3 host, the possibility of using a Mn4+/Ln3+-based dual-emitting upconversion fluorescence intensity ratio and Mn4+ upconversion lifetime as dual-modal temperature signals for accurate temperature sensing is demonstrated. It is believed that this preliminary study will offer a significant advance in exploring novel transition metal-based upconversion materials as well as self-calibrated optical thermometric media. [ABSTRACT FROM AUTHOR]

Accelerating the charge separation of semiconductor photocatalysts remains a great challenge to develop highly efficient solar-to-H2 conversion systems. Here, 2D Cu2+-doped ZnIn2S4 (Cu-ZnIn2S4) nanosheets modified with 2D MoS2 are designed and prepared via solution chemical routes. Detailed characterization reveals that the specially designed unique 2D–2D structure is critical to the high photocatalytic performance for solar H2 generation. Benefiting from the presence of a large 2D nanojunction in the 2D–2D photocatalyst, the MoS2/Cu-ZnIn2S4 has an increased contact surface area for charge transfer. The improved charge separation is demonstrated by the significant enhancement of photocurrent responses. It is found that the 2D–2D MoS2/Cu-ZnIn2S4 photocatalyst at a 6 wt% MoS2 loading amount exerts a 5463 μmol h−1 g−1 H2-evolution rate under visible light irradiation (λ ＞ 420 nm) with an apparent quantum yield of 13.6% at wavelength λ = 420 nm in 0.1 M ascorbic acid aqueous solution. This activity far exceeds those of noble metal (such as Pt, Ru, Pd or Au) loaded-Cu-ZnIn2S4 photocatalysts. The results demonstrate that the construction of a 2D nanojunction is a promising strategy to accelerate charge separation and enhance the photocatalytic performance of semiconductor photocatalysts for solar H2 generation. [ABSTRACT FROM AUTHOR]

Currently, the shortage of red components and easy aging of organic silicone still remain challenges for high-power phosphor-converted warm white light-emitting diodes (w-LEDs). Aiming to alleviate these issues, phosphor-in-glass (PiG), fabricated by co-sintering red- and yellow-emitting phosphors and low-melting glass, has been regarded as a promising color converter for w-LEDs. In this study, a Li+,Mn4+ co-doped SrMgAl10O17 red phosphor was synthesized via a conventional solid-state reaction. The as-prepared phosphor exhibits a deep red emission, ascribed to Mn4+:2Eg→4A2g spin-forbidden transition in the range of 600–700 nm with a narrow-band full width at half maximum of 55 nm, and provides an ideal broadband excitation extending from 250 to 530 nm. Impressively, the Li+ additive used as charge compensation was beneficial to enhance the Mn4+ luminescence by allowing more Mn4+ to replace Al3+. Furthermore, the developed SrMgAl10O17:Mn4+,Li+ red phosphor and commercial YAG:Ce3+ yellow phosphor co-doped inorganic PiG were successfully fabricated as color converters to substitute organic silicone. The w-LED was fabricated by combining an InGaN blue LED chip with a PiG plate. Importantly, the constructed w-LEDs exhibited superior optical performance and tuned chromaticity feature with the correlated color temperature evolved from bluish cool white (6903 K) to yellowish warm white (3717 K), and the color rendering index increased from 69.4 to 85.5, meeting the requirements for indoor lighting. [ABSTRACT FROM AUTHOR]

Due to the limitations of excitonic energy and band structure, monolayer (1L) MoS2 can only emit a narrow band of red light. Herein, we bypassed this restriction by coating 1L-MoS2 with an ultra-thin layer of highly luminescent carbon quantum dots (CQDs). These novel 1L-MoS2/CQD ultra-thin films exhibit multiple emission bands, including red light bands belonging to MoS2 and tunable bands belonging to the CQDs. A balanced intensity of these bands can be obtained by optimizing the thickness of the CQDs to ∼10 nm. By varying the excitation wavelength, the emission band of these 1L-MoS2/CQD ultra-thin films can be modulated from 550–700 nm to 450–700 nm, resulting in tunable light emission from orange (CIE0.5149, 0.3766) to yellow-green (CIE0.3175, 0.4509). These tunable emission bands are much broader than those of 1L-MoS2. However, to date, this full-color tunable emission has not been observed in other 1L-MoS2/QD thin films prepared using graphene oxide quantum dots (GOQDs) or graphene quantum dots (GQDs). [ABSTRACT FROM AUTHOR]

Herein, a strategy to achieve an 808 nm excitable water probe based on an Nd3+-sensitized core–shell upconversion nanoarchitecture is presented. Specifically, the as-synthesized Yb/Er:NaGdF4@Yb/Nd:NaYF4 active-core@active-shell nanocrystals significantly enhance the Er3+ blue, green and red upconversion emissions with the assistance of spatially confined separation between the Nd3+ sensitizers and Er3+ activators and efficient energy transfer/migration of Nd3+→ Yb3+(shell) → Yb3+(core) → Er3+. To understand the exact mechanisms for water detection, core, core–shell and core–shell–shell samples were prepared and their related water-content dependent upconversion emission and decay behaviors under 980 nm and 808 nm laser excitation systematically investigated. Different to the case of the Yb/Er:NaGdF4 core, the Nd3+-sensitized core–shell product can efficiently avoid excitation attenuation (i.e., absorption of the incident laser) and show two-separated linearity with the logarithm of H2O content at a low water content and high water content intervals, respectively, owing to the combined role of Yb3+ excited state quenching and Er3+ excited state quenching. It is expected that this study could provide insights into the design of upconversion nanoparticle based water sensors. [ABSTRACT FROM AUTHOR]

In this work, Mn2+:Zn2SiO4–Eu3+:Gd2O3 nanocomposites were fabricated following a multi-step solution route. The fluorescence intensity ratio of Mn2+ to Eu3+ in these composites exhibits remarkable temperature dependence, owing to the diverse thermal quenching behaviors of Mn2+ and Eu3+ ions. Using these nanomaterials to perform thermometry, excellent temperature sensitivity is achieved in the room temperature range. Specifically, the values of relative temperature sensitivity are all beyond 2.5% K−1 in the whole range of 303–323 K (i.e. 30–50 °C), and reach as high as 3.05% K−1 at 303 K, remarkably higher than those of other inorganic optical thermometric materials at a similar temperature. And the absolute sensitivities are all beyond 0.0089 K−1 in this temperature range, which is also a relatively high value. These results indicate the Mn2+:Zn2SiO4–Eu3+:Gd2O3 nanocomposites to be very promising nano-thermometric materials. [ABSTRACT FROM AUTHOR]

Noble-metal-free, visible-light-responsive and “green” MoS2 nanosheet modified-InVO4 heterostructures were synthesized as efficient photocatalysts for photocatalytic H2 production. The positive effect of intimate nanojunctions formed between MoS2 and InVO4 resulted in the excellent activity of MoS2/InVO4 which is even higher than that of Pt-loaded InVO4. [ABSTRACT FROM AUTHOR]

Currently, Ce3+:Y3Al5O12 phosphor converted white light-emitting diodes suffer from a deficiency of adequate red components and easy aging of the organic silicone matrix. Herein, Ce3+/Mn2+/Si4+:Y3Al5O12 phosphors were synthesized via a traditional solid-state reaction and they can emit intense red luminescence, which is attributed to the Mn2+:4T1→6A1 spin-forbidden transition under the excitation of blue light via efficient energy transfer from Ce3+ to Mn2+. Temperature-dependent emission spectra and luminescent decay curves evidence that Mn2+ activators partition into both the Al3+ octahedral and Y3+ dodecahedral sites, whereas the Si4+ sites located in the Al3+ tetrahedral site are charge compensators. Furthermore, inorganic Ce3+:Y3Al5O12 and Ce3+/Mn2+/Si4+:Y3Al5O12 dual-phase transparent glass ceramics were successfully fabricated via a low-temperature co-sintering technique to replace the phosphor in organic silicone as a color converter, and red to yellow tunable luminescence can be easily achieved by controlling the content of red phosphor in the glass matrix. Note that by combining the fabricated dual-phase glass ceramics with the InGaN blue chip, warm white light-emitting diodes with a superior optical performance and excellent heat-resistance stability were successfully constructed. [ABSTRACT FROM AUTHOR]

Blue-light-excitable Ce3+/Cr3+ codoped Y3Al2Ga3O12 persistent phosphors were synthesized by a traditional solid-state reaction method. Appropriate amounts of Cr3+ dopants were demonstrated to play an important role in improving the Ce3+ green persistent luminescence by increasing both trap states and densities and bridging the gap between shallow traps and deep ones in the host. Furthermore, benefitting from the constraining of a large amount of electrons in the deep traps, intense photo-stimulated luminescence was observed in the present products upon excitation with an 808 nm laser. Finally, as an alternative to transparent ceramic, transparent bulk Ce/Cr:Y3Al2Ga3O12 phosphor-in-glass was prepared by a facile low-temperature co-sintering route. Different from the case of Ce/Cr:Y3Al2Ga3O12 powder, the persistent luminance of phosphor-in-glass was greatly enhanced as the incident and output light could totally pass through the whole sample. [ABSTRACT FROM AUTHOR]

Currently, metal–halide perovskite semiconductors have attracted enormous attention for their excellent optical performance. However, challenging issues, such as the ability to perform large-scale synthesis as well as the thermal/moisture stability, limit their practical applications. Herein, we developed an inhomogeneous interface reaction strategy in a liquid–liquid immiscible two-phase system to realize the large-scale room temperature synthesis of novel perovskite-related Cs4PbBr6 semiconductors. Although the sizes were on the micrometer scale, the Cs4PbBr6 products exhibited bright green luminescence with a narrow line-width originating from exciton recombination confined in PbBr64− octahedra, and the photoluminescence quantum yields reached 40–45% owing to a large exciton binding energy of 222 meV. Furthermore, temperature cycling experiments demonstrated their excellent thermal stability with repeatable and reversible luminescence, and moisture-resistance experiments showed ∼65% of quantum yield loss after exposure to air for one month. Finally, a prototype white light-emitting diode device with a low correlated color temperature of 3675 K and a high color rendering index of 83 was constructed using green emissive Cs4PbBr6 and red emissive Eu2+:CaAlSiN3 phosphors, certainly indicating its promising applications in the optoelectronics field. [ABSTRACT FROM AUTHOR]