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Laser-driven white lighting has drawn great attention due to its high-brightness, high efficiency and compact size. However, the current laser lighting usually suffers from a low color rendering (Ra ∼ 60) due to the presence of a wide “Cyan cavity” (460–530 nm) in the luminescence spectrum. Herein, we report on the preparation and characterization of a novel cyan-green color converter, namely Ca3Sc2Si3O12:Ce3+,Na+ phosphor-in-glass (CSS-PiG) film. The addition of Na+ as a charge compensator greatly improved the internal quantum efficiency (IQE) of CSS:Ce3+ phosphors. Because of the good chemical stability and the matching refractive index between the glass matrix and embedded phosphors, the as-prepared CSS-PiG film exhibits an efficient cyan-green emission (with a peak at 508 nm and IQE ∼91%) and excellent thermal stability (maintaining 75% of the room-temperature emission intensity at 300 °C). Under the excitation of a 14.5 W mm−2 blue laser, the PiG film could produce a high-brightness white light with a forward luminous flux of 701 lm, a forward luminous efficacy of 112 lm W−1 and a Ra of 61. By coating a red-emitting CaAlSiN3:Eu2+ layer on the CSS-PiG film, the composite CSS-PiG/CaAlSiN3 film shows an ultra-broadband emission with a full-width at half maximum (FWHM) of 196 nm, which remarkably narrows the “Cyan cavity” and thus provides a Ra above 90. These results demonstrate that the CSS-PiG film is a promising candidate for laser lighting.

Er3+ and Yb3+ heavily doped monoclinic ZrO2 (m-ZrO2) stabilized by Nb5+ is prepared by solid-state reactions. The upconversion luminescence (UCL) of concentration optimized m-ZrO2:2%Er3+,9%Yb3+ shows a yellow emission which is found to be 4 times stronger than the red UCL of the optimized cubic ZrO2:2%Er3+,14%Yb3+. It is revealed that monoclinic ZrO2 has faster radiative transition rates of Er3+ and Yb3+ than cubic ZrO2 because of the lower crystal symmetry in the monoclinic phase that enables higher 4f–5d mixing of rare earth ions. The enhanced radiative transition allows 9%Yb3+ in the monoclinic phase to have a similar absorption of 980 nm excitation light to that of 14%Yb3+ in the cubic phase, thus retaining the lower energy back transfer from Er3+ in the green emitting state to Yb3+ and lower concentration quenching of Yb3+ in the monoclinic phase. The green and red dual-color optical thermometry behavior of m-ZrO2 has been explored. A large detectable temperature range, at which the absolute sensitivity is high, is realized through adopting this complementary optical thermometer. Repeated thermal experiments prove the stability of the m-ZrO2 as a temperature probe. Our results indicate that heavily doped m-ZrO2 is an excellent host for efficient luminescence of rare earth ions.

Tetracycline (TC) natural products possess a variety of remarkable bioactivities and diverse structures. They are an important and fertile source for developing novel drugs. As one of the most successful drug families, TC antibiotics have been in clinical use for over seven decades, and continue to make an important contribution to human health nowadays. To date, studies on TC natural products and their biosynthesis have revealed numerous novel biochemical mechanisms and regulatory elements, which facilitates the rational metabolic engineering studies for generating novel bioactive TC analogs and inspires the development of new synthetic biology tools. In this review, we provide a comprehensive overview on the discovery, biosynthesis, and engineering of the existing TC natural products. These analyses will be of great value for the discovery, design and development of novel TC drugs in the future.

Monoclinic ZrO2 (m-ZrO2) is an attractive material for photonic applications due to its low site symmetry and phonon energy. In this paper, we present detailed studies on the luminescence properties of Ti4+ and Eu3+ in m-ZrO2. In view of the continuing controversy over the origin of “intrinsic” white-blue luminescence in pristine m-ZrO2, more spectroscopic information obtained by characterizing m-ZrO2 intentionally doped with Ti4+, Ti3+ and other metal ions and extensive discussions on the general characteristics of different luminescence processes were provided to evidence the luminescence as the Ti3+ → O− charge transfer transition in the [Ti(IV)O7]10− complex due to the trace amount of Ti4+ impurity in ZrO2 reagent. Competitive absorption was observed between host exciton and oxygen–metal charge transfer processes (O2−–Ti4+, O2−–Eu3+), and even between the two types of charge transfer process because of the sharing of electrons at the top of the valence band, which greatly influenced the absorption and excitation processes. The spectral components comprising the broad excitation band of O2−–Ti4+ white-blue or Eu3+ red emissions in different phosphors were identified, and their evolutions with doping concentration were explained. The energy state locations of oxygen defects produced by intrinsic charge compensation in m-ZrO2:Eu3+ were proposed to be ∼2.41 eV above the top of the valence band by using Eu3+ for the luminescent probe. Efficient energy transfer from the [Ti(IV)O7]10− complex to Eu3+ was first observed in m-ZrO2:Ti4+,Eu3+ phosphors, which were demonstrated to be high performance ratiometric self-referencing optical thermometric materials based on the dual-emitting combination strategy, with the relative sensitivity amounting to ∼3.84% K−1. Optical thermometry not only covering the physiological temperature range but also with high relative sensitivity could be achieved upon appropriate doping.

In Ce3+ activated SrLn2O4 type phosphors (Ln = Y, Lu, Sc, etc.) only one Ce3+ center was previously reported to show a blue emission band. In this paper, we report the observation of a second Ce3+ center in SrLu2O4:Ce3+. The new center shows a red emission band peaking at 600 nm with an excitation band at 485 nm. We attributed the new center (Ce(II)) to the substitution of the Lu3+ site and the original blue center (Ce(I)) to the substitution of the Sr2+ site. Spectroscopy studies indicate that Ce(I) centers are preferentially formed at a low doping concentration and the number ratio of Ce(I)/Ce(II) decreases with increasing Ce3+ concentration until beyond 0.002. The fluorescence lifetimes of the two centers were measured for various doping concentrations. Energy transfer from Ce(I) to Ce(II) was observed. It was found that the emission intensity of Ce(II) centers reduces much faster than that of Ce(I) with increasing temperature from 83 K up to 350 K, implying their potential application in temperature sensing based on their temperature dependent intensity ratios. A relative sensing sensitivity as high as 2.28% K−1 at 283 K was achieved.

International audience; With contributions from the global natural product (NP) research community, and continuing the Raw Data Initiative, this review collects a comprehensive demonstration of the immense scientific value of disseminating raw nuclear magnetic resonance (NMR) data, independently of, and in parallel with, classical publishing outlets. A comprehensive compilation of historic to present-day cases as well as contemporary and future applications show that addressing the urgent need for a repository of publicly accessible raw NMR data has the potential to transform natural products (NPs) and associated fields of chemical and biomedical research. The call for advancing open sharing mechanisms for raw data is intended to enhance the transparency of experimental protocols, augment the reproducibility of reported outcomes, including biological studies, become a regular component of responsible research, and thereby enrich the integrity of NP research and related fields.

Nature forms S-S bonds by oxidizing two sulfhydryl groups, and no enzyme installing an intact hydropersulfide (-SSH) group into a natural product has been identified to date. The leinamycin (LNM) family of natural products features intact S-S bonds, and previously we reported an SH domain (LnmJ-SH) within the LNM hybrid nonribosomal peptide synthetase (NRPS)-polyketide synthase (PKS) assembly line as a cysteine lyase that plays a role in sulfur incorporation. Here we report the characterization of an S-adenosyl methionine (SAM)-dependent hydropersulfide methyltransferase (GnmP) for guangnanmycin (GNM) biosynthesis, discovery of hydropersulfides as the nascent products of the GNM and LNM hybrid NRPS-PKS assembly lines, and revelation of three SH domains (GnmT-SH, LnmJ-SH, and WsmR-SH) within the GNM, LNM, and weishanmycin (WSM) hybrid NRPS-PKS assembly lines as thiocysteine lyases. Based on these findings, we propose a biosynthetic model for the LNM family of natural products, featuring thiocysteine lyases as PKS domains that directly install a -SSH group into the GNM, LNM, or WSM polyketide scaffold. Genome mining reveals that SH domains are widespread in Nature, extending beyond the LNM family of natural products. The SH domains could also be leveraged as biocatalysts to install an -SSH group into other biologically relevant scaffolds., Enzymes installing an intact hydropersulfide (-SSH) group into natural products have so far not been identified. Here, the authors report the characterization of an S-adenosyl methionine-dependent hydropersulfide methyltransferase (GnmP) for guangnanmycin biosynthesis, and identification of three SH domains within several NRPS-PKS assembly lines as thiocysteine lyases.

The efficient utilization of both glucose and xylose, the two most abundant sugars in biomass hydrolysates, is one of the main objectives of biofermentation with lignocellulosic materials. The utilization of xylose is commonly inhibited by glucose, which is known as glucose catabolite repression (GCR). Here we report a GCR-based dynamic control (GCR-DC) strategy aiming at a better co-utilization of glucose and xylose, by decoupling the cell growth and biosynthesis of riboflavin as a product. Using the thermophilic strain Geobacillus thermoglucosidasius DSM2542 as a host, we constructed extra riboflavin biosynthetic pathways that were activated by xylose but not glucose. The engineered strains showed a two-stage fermentation process. In the first stage, glucose was preferentially used for cell growth and no production of riboflavin was observed, while in the second stage where glucose was nearly depleted, xylose was effectively utilized for riboflavin biosynthesis. Using the corn cob hydrolysate as a carbon source, the optimized riboflavin yields of strains DSM2542-DCall-MSS (full pathway dynamic control strategy) and DSM2542-DCrib (single module dynamic control strategy) were 5.26 and 2.26 folds higher than that of the control strain DSM2542 Rib-Gtg constitutively producing riboflavin, respectively. This GCR-DC strategy should also be applicable to the construction of cell factories that can efficiently use natural carbon sources with multiple sugar components for the production of high-value chemicals in future.

The ever-growing drug resistance problem worldwide highlights the urgency to discover and develop new drugs. Microbial natural products are a prolific source of drugs. Genome sequencing has revealed a tremendous amount of uncharacterized natural product biosynthetic gene clusters (BGCs) encoded within microbial genomes, most of which are cryptic or express at very low levels under standard culture conditions. Therefore, developing effective strategies to awaken these cryptic BGCs is of great interest for natural product discovery. In this study, we designed and validated a Transcription-Translation in One (TTO) approach for activation of cryptic BGCs. This approach aims to alter the metabolite profiles of target strains by directly overexpressing exogenous rpsL (encoding ribosomal protein S12) and rpoB (encoding RNA polymerase β subunit) genes containing beneficial mutations for natural product production using a plug-and-play plasmid system. As a result, this approach bypasses the tedious screening work and overcomes the false positive problem in the traditional ribosome engineering approach. In this work, the TTO approach was successfully applied to activating cryptic BGCs in three Streptomyces strains, leading to the discovery of two aromatic polyketide antibiotics, piloquinone and homopiloquinone. We further identified a single BGC responsible for the biosynthesis of both piloquinone and homopiloquinone, which features an unusual starter unit incorporation step. This powerful strategy can be further exploited for BGC activation in strains even beyond streptomycetes, thus facilitating natural product discovery research in the future.

Near-infrared (NIR) to visible upconversion (UC) luminescence in activator Er3+ and sensitizer Yb3+ codoped systems has been extensively studied. In this work, we report the results of Er3+-sensitized Yb3+ NIR UC emission at similar to 1000 nm originating from 2F5/2 -> 2F7/2 transition under infrared (IR) excitation at similar to 1500 nm responsible for Er3+ 4I15/2 -> 4I13/2 transition absorption. The IR to NIR UC is a desirable strategy to increase solar light utilization by reducing the spectral mismatch between the solar spectrum and crystalline silicon (c-Si) solar cells. Er3+ singly doped phosphors are mostly used for realizing the IR to NIR UC emission derived from Er3+ 4I11/2 -> 4I15/2 transition centered also at similar to 1000 nm. The efficiency of this transition, however, is limited by multiphonon relaxation and radiative transition to the 4I13/2 state. Here, Yb3+ ions are codoped in Y2O3:Er3+, and NIR UC emission with the intensity enhanced 1.5 times is achieved due to efficient energy transfer from Er3+ to Yb3+ and highly efficient Yb3+ emission. The influence of the dopants' concentrations on UC dynamics is studied. The optimal concentration under IR excitation is 5% Er3+ and 1% Yb3+. Our results indicate that introducing Yb3+ ions in Er3+ singly doped phosphors may notably improve the IR to NIR UC performance.

Er3+ and Yb3+ codoped Gd2Mo4O15 upconversion (UC) phosphors are synthesized by high temperature solid state reaction. The crystalline phase and morphology are studied in detail by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). Under 980 nm laser excitation, the phosphors show a significant green UC luminescence contributed from 2H11/2/4S3/2 → 4I15/2 transitions of Er3+, while the popular red 4F9/2 → 4I15/2 emission is quite weak. The temporal evolutions of Er3+ and Yb3+ emissions after 980 nm pulse excitation are studied as a function of Er3+ and Yb3+ concentrations. It is revealed that the weak red UC emission is due to its low emission efficiency in Gd2Mo4O15 that has a high cutoff phonon energy of 960 cm−1. The temperature sensing behaviors based on the thermally coupled 2H11/2 and 4S3/2 levels have been explored. A high absolute sensitivity of 0.00853 K−1 at 554 K is achieved and an excellent thermal durability is observed. The relative absorptance of 4I15/2 → 2H11/2 transition to the 4I15/2 → 4S3/2 transition is proposed as a good measure for evaluating the absolute sensitivity based on the comparative study of some familiar materials. Our results imply that Gd2Mo4O15 is a promising green UC phosphor for optical thermometry.

We demonstrate a blue emitting Ba2(Lu0.98La0.02)5B5O17:Ce3+ (BLLB:Ce3+) phosphor prepared by high-temperature solid-state reaction. The pure phase of Ba2Lu5B5O17 is difficult to obtain. To stabilize the crystal structure of Ba2Lu5B5O17, the larger ion radius of La3+ was added to substitute Lu3+ in raw materials. It is found that pure-phase Ba2Lu5B5O17 is successfully obtained by adding 2% La3+. Upon 348 nm excitation, a luminescence internal quantum efficiency of BLLB:Ce3+ can reach as high as 92%, which is comparable to the commercial blue phosphor BaMgAl10O17:Eu2+. The BLLB:Ce3+ phosphor shows a blue emission band peaked at 443 nm with a main excitation band peaked at 348 nm. The dependence of luminescence intensity on Ce3+ concentration was studied. The maximal luminescence intensity was observed at 1% Ce3+, which gives a critical distance of 2.41 nm between two Ce3+ ions for luminescence quenching. The emission of the present phosphor is stable with increasing temperature up to its quenching temperature of 403 K. A white light emitting diode (WLED) was fabricated based on a near UV LED chip coated with a blend of the present blue phosphor, the commercial green (Ba,Sr)2SiO4:Eu2+ and red CaAlSiN3:Eu2+ phosphors. The WLED exhibited a low correlated color temperature of 4356 K with a high color rendering index of 93.2. These results suggest that BLLB:1% Ce3+ can be utilized as a blue phosphor in UV based WLEDs.

Blue-emitting phosphors for near ultraviolet (NUV) based tri-color RGB phosphor blend converted white light emitting diodes (LEDs) have been extensively investigated in the past few years. LED chip peaked near 400 nm is the most efficient among the NUV chips currently. However, most of blue phosphors show inefficient excitation around 400 nm. Herein, a novel blue phosphor SrLu2O4:Ce3+ matching well with near 400 nm chip and showing high thermal stability has been developed. The photoluminescence spectrum presents a broad emission band peaking at 460 nm with a bandwidth of nearly 90 nm. By optimizing the Ce3+ concentration, an internal quantum efficiency (IQE) as high as 76% was achieved. Furthermore, 86% of the room-temperature emission intensity is still maintained at 150 °C, indicating a good thermal stability and practicality. A series of white LEDs were fabricated based on 405 nm chips coated with a blend of the new blue phosphor with the commercial yellow and red phosphors. High color rendering indexes (≥90) were achieved while the correlated color temperature was tuneable in the range of 3094 to 8990 K. These results suggest that SrLu2O4:Ce3+ can be utilized as a blue-emitting phosphor in NUV based white LEDs.

The red emission through upconversion (UC) upon 980 nm excitation based on Er3+/Yb3+ combination is very attractive for bioimaging applications. The intensity of the red emission is observed to be strongly dependent on the host materials. However, the origin of the behavior and the quantitative dependence remain unclear. Here, the effectiveness of the second step UC excitation from the Er3+ intermediate state 4I13/2 to the 4F9/2 level by energy transfer from Yb3+ is studied for three popular hosts (β-NaYF4, Ba5Gd8Zn4O21, and Y2O3) that have different phonon energies. Their emission efficiencies of the red emitting state are calculated, and the radiative lifetime of the 4F9/2 level in Ba5Gd8Zn4O21 is reported for the first time. We present a spectroscopic method to evaluate the relative energy transfer coefficients for the three hosts and find the coefficient increases markedly with the increase of phonon energy, reflecting the nature of phonon-assisted energy transfer. The coefficient for β-NaYF4 is 89 an...

Developing optical temperature sensors with a wider range, higher sensitivity and repeatability based on Er3+/Yb3+ doped upconverting phosphors has always been at the forefront of temperature measurement technologies. Here, we report the intense green upconversion luminescence in Er3+/Yb3+ doped δ-Sc4Zr3O12 for the first time and its temperature sensing performance is investigated. The structure of δ-Sc4Zr3O12 is given by Rietveld refinement of XRD data and the site occupancy of Er3+ ions has been determined. Compared with cubic Sc2O3 and ZrO2, under 972 nm excitation, the green emission from Er3+ centers in Sc4Zr3O12 is increased by 59-fold and 264-fold, respectively. By experimental analysis, this enhancement of upconversion luminescence is attributed to the low-symmetrical environment of Er3+, generation of Yb3+ clusters and high internal efficiency of Yb3+ emission in Sc4Zr3O12. In addition, the fluorescence intensity ratio of two green emission bands (2H11/2/4S3/2 → 4I15/2) is studied as a function of temperature ranging from 303 to 793 K in Sc4Zr3O12. The maximum sensitivity observed via calculation is 0.00634 K-1 at 573 K, and the sensitivity is still as high as 0.00534 K-1 at 793 K. The stability of a Sc4Zr3O12 thermometer is also examined via a recycling test. These findings suggest that δ-Sc4Zr3O12 is a promising upconversion host and could achieve high-sensitivity optical temperature sensing with a wide measuring range.

The Ba3Y4O9 host matrix with a low cutoff phonon energy of 585 cm−1 is first applied to upconversion (UC) luminescence (UCL) by codoping Er3+/Yb3+. The new phosphor shows an intense red UC emission which is 6.8-fold and 5.9-fold stronger than that of Y2O3 and β-NaYF4, respectively, under 980 nm GaAs laser diode (LD) excitation at a low density. A broad absorption band centered at 976 nm is observed, meaning a high adaptability to the GaAs LD required in actual applications. The optical thermometry behaviors based on the temperature dependent fluorescence intensity ratios of thermally coupled green UC bands 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 as well as the thermally coupled red UC emission bands originating from the Stark sublevels of 4F9/2 manifold have been explored. The results show that green emissions are suitable for temperatures above 350 K with the maximum sensitivity of 0.00248 K−1 at 563 K and the red emissions are appropriate for temperatures below 350 K with the maximum sensitivity of 0.00371 K−1 at 143 K in our experimental range, indicating their complementary temperature sensing ranges. Moreover, a new method is proposed for evaluating the radiative lifetime of the Er3+ 4F9/2 state based on the analysis of photoluminescence (PL) spectra and fluorescence decay curves. The radiative lifetime of 879 μs for the red emitting level in Ba3Y4O9 is achieved. Thereby, the emission efficiency of 4F9/2 in the new UCP is a little higher than that in Y2O3. Our results imply that Ba3Y4O9:Er3+/Yb3+ is a promising UCP, which could be applied to wide scope optical thermometry using a dual-color scheme.

The garnet Ca2LuZr2Al3O12 (CLZA) is a promising broad-band NIR phosphor for blue LED chips when it is doped with Cr3+. The photoelectric efficiency of the pc-LED fabricated from CLZA:Cr3+ and a 460 nm LED chip, in the 750–820 nm spectral range, was 4.1%, which was superior to the efficiency of a tungsten lamp (2.9%). In CLZA’s structure, Cr3+ occupied Ca2+/Lu3+ and Zr4+ sites and showed two luminescence centers. The crystal strength parameters of Ce3+ and Cr3+ were calculated to show the coordination environment of the dodecahedral and octahedral sites in CLZA. Low absorbance of Cr3+ was the main constraint on quantum efficiency. Ce3+ was thus introduced as a sensitizer to improve the absorbance. An efficient energy transfer process can be observed between Ce3+ and Cr3+ in CLZA. The temperature dependent properties of CLZA:Cr3+ were also studied. Two thermal processes (thermal quenching and thermal ionization) were observed and discussed in detail.

The most common yellow phosphor for wLEDs, Y3Al5O12:Ce3+ (YAG:Ce3+), suffers from a deficiency of red in its spectral content of light. In this paper, a new strategy is provided to tailor the Ce3+ spectral profile through surface-located dye molecules of ATTO-Rho101, which feature intense, broad absorption in the green-yellow spectral region of Ce3+ emission as well as bright red emission. Sphere-shaped and highly dispersed micrometer and nanometer-sized YAG:Ce3+ (micro/nano-YAG:Ce3+) was synthesized through a modified solvothermal method. Surface SiO2 coating and simultaneous dye embedding were performed on the solvothermally derived YAG:Ce3+, heat-treated micro-YAG:Ce3+ and commercial phosphors. Efficient radiative transfer/reabsorption from Ce3+ in the inner core of YAG to the dye molecules in the SiO2 outer shell, irrespective of the size of the phosphors, was demonstrated in the accumulated YAG:Ce3+@SiO2 + dye powder upon blue light excitation; this enhanced its red emission. Fluorescence microscopy was demonstrated to be a powerful tool to identify the reabsorption phenomenon of the powdered materials. Packaging the heat-treated micro-YAG:Ce3+@SiO2 + dye phosphors on blue LED chips yielded a warm wLED (Ra∼ 93), but an Ra of only ∼79 was obtained for the wLED with commercial YAG:Ce3+@(SiO2 + dye)5 due to the low concentration of phosphors dispersed in the epoxy resin and the resulting decreased reabsorption by dye molecules. Surface-protonated amine species were found to induce Ce3+→ Ce4+ oxidation upon activation by heating or photoirradiation and then quench the photoluminescence (PL) of micro-YAG:Ce3+ even after surface modification by SiO2, YAG or being embedded in an epoxy resin matrix. High calcination temperatures greatly improved the PL stability of micro-YAG:Ce3+ through the removal of surface-capped species. The dye in the silica matrix showed high stability against heating and irradiation due to the so-called "caging effects"; however, decreased photo-stability was found in commercial YAG:Ce3+@(SiO2 + dye)5 due to the incomplete and/or loose SiO2 layer grown during multiple surface modifications.

Green phosphors codoped with Ce3+ and Tb3+ have been studied extensively for application in UV-based white LEDs, but only few of them show both high luminescence efficiency and thermal stability. This study reports a new green phosphor of Ce3+ and Tb3+-codoped Ba2Lu5B5O17 prepared by a solid-state reaction. Emission color tuning from blue to green was studied as a function of Tb3+ concentration under UV excitation and well-described based on energy transfer from Ce3+ to Tb3+. The Tb3+ emission endowed the green phosphor with a high quantum yield of 86%, and a high thermal stability over the 303–483 K range was achieved. A model has been proposed to explain a general phenomenon observed in Ce3+ and Tb3+-codoped phosphors that Tb3+ emission is thermally more stable than the Ce3+ emission. A relationship between the temperature dependencies of Tb3+ and Ce3+ emissions was obtained in connection with room temperature energy transfer efficiency. The thermally stable Tb3+ emission was well-predicated using the obtained relationship. The new phosphor was employed for fabricating a UV-based white LED. A high color-rendering index of 91.4 at a low correlated color temperature of 3809 K is obtained, indicating promising application of Ba2Lu5B5O17:Ce3+,Tb3+ in solid-state lighting.

The Y3Si6N11:Ce3+ yellow phosphor shows a well-known ∼150 nm broad emission band, exhibiting a potential application in UV or blue based white LEDs. We report the observation of two Ce3+ emitting centers, the superposition of which forms the broad emission band. One center has a green emission band peaked at 539 nm (Ce1) with the first excitation band at 420 nm. The other has a red emission band peaked at 600 nm (Ce2) with the first excitation band at 485 nm. The two Ce3+ centers are assigned to the substitution for two Y sites in Y3Si6N11. It was found that the Ce2 emission intensity is continuously enhanced relative to that of Ce1 with an increasing Ce3+ concentration, thus leading to a redshift of the broadband. Meanwhile, a more notable fluorescence lifetime shortening of Ce1 compared to Ce2 with an increasing Ce3+ concentration was observed. These results suggest the occurrence of energy transfer from Ce1 to Ce2. The temperature-dependent luminescence intensity of Y3Si6N11:Ce3+ was also studied in the range of 93 to 473 K.

Er3+-induced intensity enhancement of ∼2 μm emission is observed in 2 atom % Tm3+ doped Lu2O3 under 782 nm excitation. The maximum enhancement reaches 41.9% with only 0.05 atom % Er3+. Er3+ introduces a new quantum cutting process which is proved to be a Tm3+ → Er3+ → Tm3+ forward-backward energy transfer (FBET) system. The FBET system is observed to work efficiently even at very low Er3+ concentration. Thus, energy loss due to energy migration among Tm3+ ions is suggested to be suppressed by the FBET process. The Tm3+ → Er3+ → Tm3+ FBET system may be a new route to improve the performance of Tm3+ lasers.

In this paper, we synthesized series of Eu 2+ activated CaO ceramic powders by conventional solid state reaction. Using NH 4 Cl as a reducing additives, the Eu 3+ has been successfully reduced to Eu 2+ . An intense blue emission peaked at 460 nm from Eu 2+ was observed. The luminescent intensity of the doping-optimized CaO:Eu 2+ sample can be as high as 106% of commercial BAM blue phosphor under 400 nm near-ultraviolet (NUV) excitation. The effect of Eu 2+ and NH 4 Cl contents on photoluminescence properties and crystal phase formation have been investigated, respectively. The thermal stable property which is an important performance for LED application has also been measured. The emission intensity at 120 °C can maintain 94% of that at room temperature. Our results suggest that CaO: Eu 2+ ceramic powder could be used as a promising blue emitting phosphor for NUV chip based white LEDs.

Forming solid solutions through cation substitution is an efficient way to improve the luminescence properties of Ce3+ or Eu2+ activated phosphors and even to develop new ones, which is badly needed for phosphor-converted white LEDs. Here, we report new color tunable solid solution phosphors based on Eu2+ activated K2Al2B2O7 as a typical case to demonstrate that, besides crystal field splitting of 5d levels, centroid shift and Stokes shift can be dominant in tuning excitation and emission spectra as well as thermal stability of solid solution phosphors, both of which were previously considered to be negligible. Moreover, a general model involving the inductive effect of neighboring cations is proposed to explain the obvious variations in centroid shift and Stokes shift with cation substitution. Our work is propitious for the construction of more reasonable structure-property relations and thus offers theoretical guidance for designing solid solution phosphors.

The step energy transfers from Pr3+ 4f5d state to Ce3+ 5d state followed by energy back transfer from Ce3+ 5d state to Pr3+ 1D2 level are studied. The Ce3+→Pr3+ energy back transfer upon Pr3+ 4f5d excitation is found to be more efficient than the normal Ce3+→Pr3+ energy transfer upon Ce3+ 5d excitation. The efficient energy back transfer is attributed to preferential excitation of the Ce3+ ion with an adjacent Pr3+ surrounding in Pr3+→Ce3+ energy transfer of the first step, whereas Ce3+ is excited randomly in the normal energy transfer. The efficiencies of Ce3+→Pr3+ energy back transfer as a function of Ce3+ and Pr3+ concentration are evaluated, respectively.

CaSc2O4 phosphors codoped with 0.2% Er3+ and various concentrations (0–15%) of Yb3+ are prepared by high temperature solid-state reaction. Two Er3+ luminescence centers are observed and they are assigned to substitution for Ca2+ site (Er3+(I)) and Sc3+ site (Er3+(II)), respectively. We find that the Er3+(I) centers are preferentially formed at low doping concentration and their number starts to decrease along with the increase of the Er3+(II) centers on increasing Yb3+ concentration. Meanwhile, intense upconversion luminescence (UCL) with color tuning from green to red is observed upon 980 nm excitation. The decomposition of the UCL spectra exhibits the main contribution from the Er3+(I) centers in the range of Yb3+ concentration of this work. This result is attributed to efficient emissions of the Er3+(I) centers for the long lifetimes of Er3+(I) both on the green and red emitting levels. Furthermore, we have observed the UCL intensity of CaSc2O4: 0.2% Er3+, 15% Yb3+ is 4 times as strong as that in Y2O3: 0.2 Er3+, 15% Yb3+.

The dehydratase domains (DHs) of the iso-migrastatin (iso-MGS) polyketide synthase (PKS) were investigated by systematic inactivation of the DHs in module-6, -9, -10 of MgsF (i.e., DH6, DH9, DH10) and module-11 of MgsG (i.e., DH11) in vivo, followed by structural characterization of the metabolites accumulated by the mutants, and biochemical characterization of DH10 in vitro, using polyketide substrate mimics with varying chain lengths. These studies allowed us to assign the functions for all four DHs, identifying DH10 as the dedicated dehydratase that catalyzes the dehydration of the C17 hydroxy group during iso-MGS biosynthesis. In contrast to canonical DHs that catalyze dehydration of the β-hydroxy groups of the nascent polyketide intermediates, DH10 acts in a long-range manner that is unprecedented for type I PKSs, a novel dehydration mechanism that could be exploited for polyketide structural diversity by combinatorial biosynthesis and synthetic biology.

Emission spectra of Tm 3+ and Yb 3+ codoped Lu 2 O 3 are studied as a function of the dopant concentration upon 980 nm excitation. The upconverted near infrared emission around 811 nm from Tm 3+ : 3 H 4 → 3 H 6 transition is observed due to two step energy transfers from Yb 3+ through Tm 3+ : 3 F 4 as the intermediate level. The optimal dopants concentrations for the strongest upconversion emission are 0.1 mol% Tm 3+ and 4 mol% Yb 3+ . The dependence of energy transfer coefficients for the two step energy transfers on Tm 3+ and/or Yb 3+ concentration is studied. The obtained results indicate that the excitation diffusions among Yb 3+ ions and among Tm 3+ ions mainly control the energy transfer rates for the optimal dopants concentrations and thus dominate the energy transfer upconversion process.