Absorption Spectrum Of Chlorophyll Research Articles

A narrow-band blue emitting phosphor by co-doping Bi3+ and alkali metal ions (Li+, Na+ and K+) with dual luminescence center

The technology of solid-state lighting has developed for decades in various industries. Phosphor, as an element part, determines the application domain of lighting products. For instance, blue and red-emitting phosphors are required in the process of plant supplementing light, arrow-band emitting phosphors are applied to backlight displays, etc. In this work, a Bi3+-activated blue phosphor is obtained in a symmetrical and compact crystal structure of Gd3SbO7 (GSO). Then, the co-doping strategy of alkali metal ions (Li+, Na+, and K+) is used to optimize the performance. The result shows that the photoluminescence intensity is increased by 2.1 times and 1.3 times respectively by introducing Li+ and K+ ions. Not only that, it also achieves narrow-band emitting with the full width of half-maximum (FWHM) reaching 42 nm through Na+ doping, and its excitation peak position also shifts from 322 to 375 nm, which can be well excited by near-ultraviolet (NUV) light emitting diode (LED) chips (365 nm). Meanwhile, the electroluminescence spectrum of GSO:0.6 mol%Bi3+,3 wt%Na+ matches up to 93.39% of the blue part of the absorption spectrum of chlorophyll a. In summary, the Bi3+-activated blue phosphor reported in this work can synchronously meet the requirements of plant light replenishment and field emission displays.

A novel light source for post-harvest lettuce preservation based on chlorophyll absorption spectrum

With increased consumers’ demand for safe and healthy food, LED lighting for photobiology has received wider attention. In order to prolong the preservation time of the post-harvest lettuce, this paper documents a novel light source designed for preservation based on the chlorophyll absorption spectrum. Effects of intermittent exposure (35 μmol m−2 s−1) on sensory quality and chlorophyll content in fresh lettuce were investigated during 3 days storage at 20°C ± 1°C and 60% ± 1% humidity using dark as the control. The results show that the lighting reduced the colour difference value of lettuce by 23.5% compared with the dark. The content of chlorophyll was 19.7% more than in the dark. The lighting with the novel light source inhibited the decline in the colour difference value − a/ b of lettuce and delayed the degradation of chlorophyll.

A novel reddish‐orange emitting NaSrBiTeO6:Sm3+ phosphor with high moisture resistance and thermostability for horticultural light emitting diode applications

AbstractA sequence of reddish‐orange emitting NaSrBi(1−x)TeO6:xSm3+ phosphors were successfully composited by a favorable solid‐phase chemical process. The sintering temperature is optimized as 850°C. NaSrBiTeO6 (NSBTO):Sm3+ samples were assigned to the cubic double‐perovskite structure, exhibiting the space group of Fmm (225). Photoluminescence emission spectra display the main peaks at 562, 598, 645, and 705 nm at 404 nm excitation. Among them, the most intense emission peak is at 645 nm. The concentration‐quenching mechanism of Sm3+ follows the interaction between electric dipoles and quadrupoles. The asymmetric ratio (I(4G5/2‐6H9/2)/I(4G5/2‐6H5/2) of NSBTO:2 mol%Sm3+ phosphor is extracted as 4.96. The optimum NSBTO:2 mol%Sm3+ phosphor has excellent thermal stability with a remained emission intensity riches 93.61% (420 K). After testing with high‐pressure water steam at various periods, the phosphor remains chemically stable for moisture resistance. For the NSBTO:2 mol%Sm3+ phosphor, the satisfactory color purity and low correlated color temperature (CCT) are obtained with 99.9% and 1494 K, respectively. The electroluminescence spectra of the prepared red light emitting diode (LED) are in conformity with the phytochrome absorption spectra of chlorophyll a, chlorophyll b, PFR, and PR. The white light‐emitting diode (w‐LED) is also perfectly packaged, obtaining an efficient color rendering index (Ra) of 92.12 and CCT of 5553 K. These exceeding optical properties certified that NaSrBi(1−x)TeO6:xSm3+ demonstrates promising prospects and can be efficiently applied in horticultural LED applications.

Synthesis of Bi3+ and Eu3+ co-doped Na4CaSi3O9 blue-red light tunable emission phosphors for inducing plant growth

Sunlight is an important factor in plant growth. In this regard, both blue and red lights provide significant contributions. Blue–red light dual-emission phosphors, which can be achieved by regulating energy transfer between two independent luminous centers, have recently been investigated extensively. In this study, Bi3+ and Eu3+ co-doped Na4CaSi3O9 (NCSO: Bi3+, Eu3+) phosphors are successfully synthesized via a high-temperature solid-phase method at approximately 900 °C for a few hours. X-ray powder diffraction is used to verify the crystal structure, phase purity, and structural refinement of the NCSO-based phosphors. Upon light excitation at 299 nm, the phosphors show blue–red dual emission. The blue emission (300–500 nm) may have originated from the 3P1 → 1S0 transition of Bi3+, whereas the red emission (575–725 nm) is attributable to the 5D0 → 7FJ (J = 1, 2, 3 and 4) transition of Eu3+ ions. Energy transfer from Bi3+ to Eu3+ is systematically investigated and the thermal stability of the phosphors is analyzed using temperature-dependent spectroscopy. The emission spectra of NCSO: Bi3+, Eu3+ are consistent with the absorption spectra of chlorophyll a, chlorophyll b, phytochrome PR, and phytochrome PFR. These results indicate that the obtained phosphors exhibit significant potential for inducing plant growth.

High thermally stable deep red-emitting Sb3+,Ho3+-codoped Cs2NaScCl6 double perovskite for plant lighting

Lead-free halide double perovskite has received widespread attention due to its excellent optical performance. However, the lack of deep red light and poor heat quenching resistance severely limit its application in plant lighting field. In this work, Ho3+ was introduced into the thermally stable Cs2NaScCl6 host, exhibiting a deep red emission of 660 nm. By constructing an energy transfer channel between Sb3+ and Ho3+, the photoluminescence quantum yield (PLQY) of Cs2NaScCl6:1%Sb3+,40%Ho3+ rises up to 53.8%, that is increased by 17 times, and its emission intensity can still be maintained by 80% at 423 K, exhibiting good heat quenching resistance. The obtained Cs2NaScCl6:1%Sb3+,40%Ho3+ and Cs2NaScCl6:1%Sb3+ with blue light emission were employed for fabricating a light-emitting diode (LED) device with a 340 nm UV chip, and its emission spectrum matches well the absorption spectra of chlorophyll A and chlorophyll B with the high resemblance of 70% and 75%, making it suitable for use as an artificial light source to control the growth process of plants in the field of plant lighting.

On the importance and challenges of modelling extraterrestrial photopigments via density-functional theory

The emergence of oxygenic photosynthesis was a major event in Earth’s evolutionary history and was facilitated by chlorophylls (a major category of photopigments). The accurate modelling of photopigments is important to understand the characteristics of putative extraterrestrial life and its spectral signatures (detectable by future telescopes). In this paper, we perform a detailed assessment of various time-dependent density-functional theory (TD-DFT) methods for predicting the absorption spectra of chlorophyll a, with particular emphasis on modern low-cost approximations. We also investigate a potential extraterrestrial photopigment called phot0 and demonstrate that the electronegativity of the metal ion may exert a direct influence on the locations of the absorption peaks, with higher electronegativity inducing blue-shifting and vice-versa. Based on these calculations, we established that global-hybrid approximations with a moderate percentage of exact exchange – such as M06 and PW6B95 – are the most appropriate compromise between cost and accuracy for the computational characterisation of photopigments of astrobiological interest. We conclude with a brief assessment of the implications and avenues for future research.

Structure and luminescence of a high-efficient blue-red-emitting Na2BaMg(PO4)2: Eu2+, Mn2+ phosphor for plant growth LEDs

New dual-emitting phosphor Na2BaMg(PO4)2: Eu2+, Mn2+ is prepared via conventional sintering method. The structural and luminescent properties of as-synthesized phosphor were systematically studied by experimental characterization and theoretical calculation. Utilizing the Eu2+→Mn2+ energy transfer, this phosphor exhibits efficient double-band emissions at 415 and 620 nm, which has a good match with the absorption spectra of chlorophyll A/B and phytochrome in plants. The energy transfer mechanism had been investigated through emission intensity and decay lifetime variation using Reisfeld's approximation method. Na2BaMg(PO4)2: Eu2+, Mn2+ shows promising properties like good thermal stability (75% emission intensity maintenance at 200 °C) and high quantum efficiency (QE > 80%). A prototype LED was fabricated using optimized phosphor and NUV chip, which exhibits two distinct emission peaks modulating an optimum action spectrum for plant absorption. All results indicate that Na2BaMg(PO4)2: Eu2+, Mn2+ is of great potential as converted component for plant growth LEDs.

An efficient protocol for excited states of large biochromophores.

Efficient energy transport in photosynthetic antenna is a long-standing source of inspiration for artificial light harvesting materials. However, characterizing the excited states of the constituent chromophores poses a considerable challenge to mainstream quantum chemical and semiempirical excited state methods due to their size and complexity and the accuracy required to describe small but functionally important changes in their properties. In this paper, we explore an alternative approach to calculating the excited states of large biochromophores, exemplified by a specific method for calculating the Qy transition of bacteriochlorophyll a, which we name Chl-xTB. Using a diagonally dominant approximation to the Casida equation and a bespoke parameterization scheme, Chl-xTB can match time-dependent density functional theory's accuracy and semiempirical speed for calculating the potential energy surfaces and absorption spectra of chlorophylls. We demonstrate that Chl-xTB (and other prospective realizations of our protocol) can be integrated into multiscale models, including concurrent excitonic and point-charge embedding frameworks, enabling the analysis of biochromophore networks in a native environment. We exploit this capability to probe the low-frequency spectral densities of excitonic energies and interchromophore interactions in the light harvesting antenna protein LH2 (light harvesting complex 2). The impact of low-frequency protein motion on interchromophore coupling and exciton transport has routinely been ignored due to the prohibitive costs of including it in simulations. Our results provide a more rigorous basis for continued use of this approximation by demonstrating that exciton transition energies are unaffected by low-frequency vibrational coupling to exciton interaction energies.

Rhodopsin driven microbial CO2 fixation using synthetic biology design.

Solar energy is the ultimate source of sustainable energy. One-hour of the sunlight energy received by the earth has more energy than the whole human needs in a year. Microorganisms and plants use sunlight as energy sources to fix CO2 and drive biosynthesis of biomass, which is the foundation of the biosphere on the earth. Sunlight energy harvesting is the first crucial step to use the solar energy. Chlorophyll-based and rhodopsin-based light harvesting systems are two distinct and absorbance complementary mechanisms (Bryant & Frigaard, 2006; Finkel et al., 2013). Classic chlorophyll-based systems in photosynthesis have been well documented. The discovery of proteorhodopsin (PR) has changed the view of its role in natural ecosystem (Beja et al., 2000; Beja et al., 2001; Rozenberg et al., 2021). PR is globally abundant and widely distributed in microbes (Beja et al., 2000; Beja et al., 2001; Campbell et al., 2008; Finkel et al., 2013; Fuhrman et al., 2008; Jing et al., 2018; Rusch et al., 2007; Sabehi et al., 2005). A recent survey in the Mediterranean Sea and the Eastern Atlantic Ocean suggested that microbial rhodopsins-based systems could contribute to the same amount of light energy harvesting as chlorophyll-based systems (Gomez-Consarnau et al., 2019). In comparison to chlorophyll-based photosynthesis that assembles a large and relative complex network of light-harvesting, a rhodopsin-based functional activity only involves one single gene encoded membrane protein with retinal. Rhodopsins are light-activated ion transporters, including light-driven pumps and light-gated channels (Ernst et al., 2014; Rozenberg et al., 2021). Among them, proton-pumping PR has been well-studied and documented. It can act as a light activated proton pump, harvesting solar energy to pump out protons for the generation of a proton motive force which supports ATP synthesis (Steindler et al., 2011), biomass growth (Gómez-Consarnau et al., 2007), substrate uptake (Gómez-Consarnau et al., 2016), and bacterial survival (Gómez-Consarnau et al., 2010). The simplicity of rhodopsin offers a new approach to genetically engineering non-phototrophic cells for harvesting light energy. Engineered Escherichia coli with rhodopsin was reported to have a long-term viability (Song et al., 2019), enhanced biomass growth (Kim et al., 2017) and accelerated target compound biosynthesis (Toya et al., 2022). The conventional concept of rhodopsin phototrophy is based on light-driven extra energy supply, such as increasing ATP to promote microbial carbon fixation. It has been reported that PR powered anaplerotic CO2 fixation could occur in Dokdonia sp. MED134 (Palovaara et al., 2014), and in marine bacteria (Alonso-Sáez et al., 2010; Beier et al., 2015; Jing et al., 2022; Kirchman et al., 2007; Koedooder et al., 2018; Moran & Miller, 2007; Pinhassi et al., 2016; Smith et al., 2010). Despite microbial rhodopsins representing the most widespread phototrophic system at the genetic level (Finkel et al., 2013), the relationship between rhodopsin and microbial autotrophic carbon fixation is still unclear. It is possible that the significance of rhodopsin in global carbon cycling could be underestimated. Both ATP and reducing equivalents (e.g., NADH or NADPH) are required for cell growth. We reason that rhodopsin cannot drive the microbial autotrophic CO2 fixation pathway on its own because the system lacks electron donor. When an organic compound such as formate was used as the electron donor, Gloeobacter rhodopsin-expressing Ralstonia eutropha can increase 20% biomass growth in the light (Davison et al., 2022). Formate is split into CO2 and NADH when it gets into Ralstonia eutropha. Extra ATP can be produced by the light activated proton pump Gloeobacter rhodopsin. Chlorophyll-based photoautotrophic systems obtain electron donors from light-driven water splitting, which can be used to generate NADPH. Rhodopsin phototrophy, unlike chlorophyll-based photosynthesis, is independent of electron transfer and is not involved into any known redox processes (Hassanzadeh et al., 2021). We hypothesised that a closed redox loop can be constructed by integrating rhodopsin with an electron donor. In such a rhodopsin-based autotrophic system, an electron donor could be an electrode powered by a solar panel, and an electron shuttling molecule such as riboflavin could transfer the electron from the electrode to rhodopsin-expressing microbes (Davison et al., 2022). In this designed system, a rhodopsin-based photoelectrosynthetic system could drive autotrophic growth of bacteria using CO2 as the sole carbon source, and with light as the only energy input (Figure 1). The proton motive force generated from rhodopsin has been proven to enable microbes to overcome thermodynamically unfavourable processes to reduce NAD+ and generate NADH (Tefft & TerAvest, 2019). Then the light-activated rhodopsins can drive the reversing function of NADH dehydrogenase for the synthesis of NADH from quinones. Rhodopsin is not only a “booster” but also “drive” electron transfer. We therefore established a photoelectrochemical CO2 fixation system with engineered Ralstonia eutropha, in which the heterogeneously expressing Gloeobacter rhodopsin powered both ATP and NADH formation to drive CO2 fixation. The engineered Ralstonia eutropha accepted electrons from an electrode mediated by an electron shuttle (Davison et al., 2022) (Figure 1). Such Ying (electrons) and Yang (protons) interactions not only power ATP synthesis but also form redox reactions to complete the cycle of biosynthesis. The rhodopsin-based CO2 fixation system enabled Ralstonia eutropha to perform autotrophic growth using light as the only energy source and CO2 as the sole carbon source. Since microbial rhodopsin is simple and able to be expressed in many different microbes, such rhodopsin-based photoelectrosynthesis can be extended to a broad range of microbes for CO2 fixation, which could open a new frontier in “rhodopsin-based photosynthesis.” The light intensity on the solar panel was only 2 μmol m−2 s−2 to generate ~1.6–1.8 V to drive autotrophic growth of R. eutropha-GR in the photo-electrosynthetic system (Figure 1). Given that the light toelectricity efficiency in solar panel is usually 20%, the overall solar energy to biomass in photo-electrosynthetic system was about 4%, which is comparable to conventional chlorophyll-based photosynthesis (Davison et al., 2022). The design of rhodopsin-based photosynthesis can be further improved by learning the lessons from chlorophyll-based system (Ort et al., 2015), including light capture, carbon capture and smart consortium. Rhodopsins absorb wavelength around 530 nm which is complementary to the chlorophyll system. Directed evolution is able to extend the rhodopsin's light absorption. Gloeobacter violaceus rhodopsin was reported to be evolved into 70 variants with absorption maxima shifted by up to ±80 nm (Engqvist et al., 2015). With novel retinal analogues, rhodopsin was able to expand the absorbance band, tailing out to near-infrared wavelengths (Ganapathy et al., 2017). The quantum efficiency of rhodopsins can reach almost 70% (Govindjee et al., 1990; Yang et al., 2022). Many microbes can take up both CO2 and bicarbonate using their various channels, the extra energy supplied by light-activated rhodopsins may increase the flux of inorganic carbon into cells, enhancing carbon capture efficiency. Another potential application of rhodopsin is to create a consortium or coculture containing both chlorophyll- and rhodopsin-based microbes. At least 10% of energy from photosynthetically active radiation is lost in chlorophyll-based photosynthesis due to its weak absorbance in the green band (Zhu et al., 2008). The loss of light utilisation is a key factor for the low efficiency of photosynthesis for CO2 reduction. Notably, chlorophyll's absorption spectrum is complemented by rhodopsin's (Walter et al., 2010). Therefore, the consortium or coculture is expected to improve the utilisation of solar energy (Figure 2). The same goal can be accomplished by cloning rhodopsin into chlorophyll-containing bacteria using synthetic biology design. To address the problem that two photosystems compete for the same photon sources, rhodopsin has been reported to replace photosystem I (PSI) in Synechocystis sp. PCC6803, increasing the growth rate by 16% (Chen et al., 2019). The expanded light absorbance of rhodopsin enables the design of synthetic mixed consortium to achieve maximal light capture and CO2 fixation per unit of surface area (Figure 2). Microbial rhodopsins are ubiquitous and multifunctional in the biosphere (Rozenberg et al., 2021). The roles of microbial rhodopsins in nature will be better understood through further studies on molecular microbial ecology and biochemistry (Chazan et al., 2022; Pushkarev et al., 2018). The exploration of rhodopsins is consistently updating our perspectives on their structures, functions and molecular mechanisms. The applications of rhodopsins can lead to new research of photosynthesis via advanced design of synthetic biology (Davison et al., 2022; Inoue et al., 2021), promoting for faster and more efficient biosynthesis and CO2 fixation. WEH proposed the idea. WEH and WT write the manuscript. WEH thanks EPSRC (EP/M002403/1 and EP/N009746/1) and BBSRC (BB/M000265/1) in the UK for finance support. The authors declare no competing financial interest.

Conversion of UV light to dazzling reddish orange light with robust color purity for plant growth in biocompatible glasses

Remarkable red luminescence was achieved from synthesized lithium zinc borate glasses (LBZ) composed of Eu3+ and Gd3+ ions by melt quenching for greenhouse applications. LBZ: Gd3+ glass exhibited emission at 311 nm (6P7/2→8S7/2) upon 265 nm excitation. By exciting at 393 nm, LBZ: Eu3+ glass emits a dazzling reddish-orange emission at 612 nm (5D0→7F2). Due to successful energy migration from Gd3+ to Eu3+, co-doped glasses generate more exquisite reddish light at 612 nm with high color purity than independently (Eu3+) doped glass under 265 nm of UV irradiation. Various fluorescence methods were used to demonstrate energy transmission. Notably, the enhanced luminescence extending from 580 to 700 nm pertaining to co-doped glasses was correlated with the absorption spectrum of chlorophyll. The results of in vitro cell viability confirm the non-cytotoxicity and a high level of biocompatibility. From the results, the non-cytotoxic co-doped (1.0Gd3+-1.0Eu3+)-glass has been found to be a potential candidate as a biocompatible greenhouse glass for plant growth.

Metal To Metal Charge Transfer Induced Efficient Yellow/Far‐Red Luminescence in Na2Ca3(Nb, Ta)2O9:Bi3+ toward the Applications of White‐LEDs and Plant Growth Light

AbstractRed and far‐red spectral components are the basics for color rendering improvement of illumination devices and growth regulation of plants, respectively. Establishing a feasible design principle in solid state materials for the red/far‐red phosphors is significant but challenging. Realizing metal to metal charge transfer (MMCT) in Bi3+‐doped phosphors is a new strategy to target the red/far‐red luminescence. As a proof of concept, the MMCT state involving the ground state of Bi3+ ion and the excited state of host (Nb/Ta)5+ cations in Na2Ca3(Nb, Ta)2O9:Bi3+ induces efficient and tunable yellow/far‐red luminescence (peaking at 597–667 nm). Moreover, benefited from the appropriate distance between Bi3+ and (Nb/Ta)5+ ions, Na2Ca3(Nb, Ta)2O9:Bi3+ possess intense absorption in near‐ultraviolet region and no absorption in visible region. The plant growth light with the blending of Na2Ca3Nb2O9:Bi3+ far‐red phosphor and BAM:Eu2+ blue phosphor yields broadband electroluminescence covering almost the entire absorption spectra of chlorophyll and phytochrome, which is superior to the Cr3+‐ and Mn4+‐based light‐emitting diode (LED) devices. The white‐LED device by employing Na2Ca3Ta2O9:Bi3+ yellow phosphor as the essential component yields full‐spectrum warm white light with high color indexes.

Novel Dual-Excitation and Dual-Emission Materials: Eu2+,Pb2+ Co-doped Core-Shell-Structured CaS@CaZnOS Phosphors and Their Application for Highly Efficient Photosynthesis of Plants.

Eu2+,Pb2+-doped core-shell-structured CaS@CaZnOS phosphors were synthesized by a two-step high-temperature solid-phase method. The as-synthesized CaS:Eu2+,Pb2+@CaZnOS:Pb2+ phosphors possess excellent dual-excitation and dual-emission (DE2) luminescent properties, which give rise to red emission peaking at 650 nm under green excitation, derived from the core CaS:Eu2+,Pb2+, and blue emission peaking at 424 nm, originating from the shell CaZnOS:Pb2+, under ultraviolet (UV) excitation. In addition, tunable red/blue emission can be achieved by changing the doping concentration of Pb2+ in the CaZnOS shell. The red/blue dual emission of core-shell DE2 phosphors under excitation of UV and green light significantly matches with the absorption spectrum of chlorophyll (a, b); hence, the as-prepared phosphors are excellent solar spectral conversion (SSC) auxiliaries of plastic films or laminated glass for greenhouses and provide ideas for creating more efficient and practically valuable SSC auxiliaries. The DE2 properties are described, and the energy transfer mechanism from Pb2+ to Eu2+ in the core is proposed and discussed in detail.

Investigation of Chlorophyl-a Derived Compounds as Photosensitizer for Photodynamic Inactivation

Chlorophyll has unique physicochemical properties which makes them good as photosensitizer of Photodynamic Inactivation (PDI). The physicochemical properties of chlorophyll as photosensitizer can be optimized through several routes.  One of the possible route is by replacing the metal ion center of chlorophyll with other ions. In this research, the effect of coordinated metal ion in the natural chlorophyll-a was studied for bacterial growth (S. aureus) inhibition. The replacement of metal in the center of chlorophyll hopefully can improve the intensity of Intersystem Crossing Mechanism (ISC) lead to the formation of singlet oxygen species. The chlorophyll a and b were isolated from spinach via precipitation technique using 1,4 dioxane and water. The chlorophyll a and b were separated using sucrose column chromatography. The thin layer chromatography result showed that chlorophyll a (Rf: 0.57) had been well separated with chlorophyll b (Rf: 0.408). The absorption spectra of chlorophyll a and b showed that the Soret band was observed at 411 and 425 nm, while the Q band appeared at 663 and 659 nm. Replacement of metal ion center shifted the Soret band of chlorophyll- a derivatives to lower energy region, while Q-band was slightly shifted to the higher energy region. The absorption and the fluorescence intensity were  also observed decreasing after ion replacement. The Inhibition activity investigation over S. aureus showed the highest inhibition activity was exhibited by Zn-pheophytin-a (66.8%) followed by chlorophyll a (30.1 %) and Cu-pheophytin-a (0%). The inhibition activity is correlated with decreasing fluorescence intensity. The formation of singlet oxygen by ISC mechanism is hypothesized to deactivate the excitation state of Cu-pheophytin-a. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Tunable blue-red dual emission via energy transfer in Na4CaSi3O9: Ce3+, Mn2+ phosphors for plant growth LED

Along with the rapid development of modern agriculture, plant growth requires better light quality. Blue and red light play a crucial role in plant growth, so achieving blue-red dual light emission is urgently needed. The energy transfer (ET) between two independent luminous centers is an effective means to regulate the blue-red dual emission. Hence, Ce3+-Mn2+ co-doped Na4CaSi3O9 (NCSO) phosphors are successfully synthesized by a conventional high-temperature solid-state method. The crystal structure and phase purity of NCSO phosphors are confirmed by X-ray powder diffraction (XRD) and Rietveld structure refinement. Ce3+ and Mn2+ co-doped NCSO phosphors exhibit blue - red dual emission under the excitation of 336 nm. The blue emission mainly comes from the 5d-4f transition of Ce3+, while the red emission belongs to the 4T1(4G)-6A1(6S) spin-forbidden transition of Mn2+. The emission spectra of NCSO: Ce3+, Mn2+ is in good agreement with the absorption spectra of chlorophyll. The ET process from Ce3+ to Mn2+ is studied and the temperature-dependent luminescence is examined to verify the thermal stability of phosphor. These results indicate that the as-obtained phosphors may have potential applications in plant growth lighting.

Simulation of plant growth spectrum with high-fitness based on spectral segmentation fitting

Light emitting diodes (LEDs) are considered next-generation light sources. Because of their narrow spectral distribution, fast response and convenient adjustment, LEDs are widely used in spectrally adjustable light sources. In order to determine the best combination of LEDs to obtain a high-fitness plant growth spectrum, in this paper we use Gaussian function model to construct the spectral distribution of monochromatic LEDs, choose the absorption spectrum of chlorophyll b as the target spectrum. Divide the spectrum into gentle wavebands and steep wavebands and use the combination of equal-interval and unequal-interval peak wavelength LEDs to fit the target spectrum, then compared eight experiments and determined the best number of LEDs used in different wavebands of the target spectrum. Finally, this paper use the LEDs of Epitex series to fit target spectrum, experimental results show that correlation coefficient R2 can reach 0.9673 and 0.9675.

Design of highly efficient deep-red emission in the Mn4+ doped new-type structure CaMgAl10O17 for plant growth LED light.

The auxiliary light equipment for plant growth requires phosphor-converted light-emitting-diodes (pc-LEDs) with high luminous efficiency and a stable structure, and the properties of phosphors highly determine the performance of the pc-LEDs. This work reports a deep-red emitting phosphor with an ultra-wide response range which is regarded as CaMgAl10O17:Mn4+. The absorption range spans the ultraviolet, near-ultraviolet, blue, and green light regions from 250 to 550 nm. Under the excitation of the best excitation position at 343 nm, deep-red light at 654 nm is emitted, and the quantum efficiency is as high as 86.7%. The luminous efficiency of the two pc-LED devices prepared based on CaMgAl10O17:Mn4+ with 395 and 460 nm chips reached 54.3 and 59.6 lm W-1, respectively. The spectra of the two pc-LEDs exhibit high resemblance to the absorption spectra of chlorophyll A and B in plant growth photosynthesis. These indicate that the CaMgAl10O17:Mn4+ phosphor can be an excellent candidate for plant growth LED light.

Accurate Computation of the Absorption Spectrum of Chlorophyll a with Pair Natural Orbital Coupled Cluster Methods.

The ability to accurately compute low-energy excited states of chlorophylls is critically important for understanding the vital roles they play in light harvesting, energy transfer, and photosynthetic charge separation. The challenge for quantum chemical methods arises both from the intrinsic complexity of the electronic structure problem and, in the case of biological models, from the need to account for protein–pigment interactions. In this work, we report electronic structure calculations of unprecedented accuracy for the low-energy excited states in the Q and B bands of chlorophyll a. This is achieved by using the newly developed domain-based local pair natural orbital (DLPNO) implementation of the similarity transformed equation of motion coupled cluster theory with single and double excitations (STEOM-CCSD) in combination with sufficiently large and flexible basis sets. The results of our DLPNO–STEOM-CCSD calculations are compared with more approximate approaches. The results demonstrate that, in contrast to time-dependent density functional theory, the DLPNO–STEOM-CCSD method provides a balanced performance for both absorption bands. In addition to vertical excitation energies, we have calculated the vibronic spectrum for the Q and B bands through a combination of DLPNO–STEOM-CCSD and ground-state density functional theory frequency calculations. These results serve as a basis for comparison with gas-phase experiments.

Establishment of the Qy Absorption Spectrum of Chlorophyll a Extending to Near-Infrared.

A weak absorption tail related to the Qy singlet electronic transition of solvated chlorophyll a is discovered using sensitive anti-Stokes fluorescence excitation spectroscopy. The quasi-exponentially decreasing tail was, at ambient temperature, readily observable as far as −2400 cm−1 from the absorption peak and at relative intensity of 10−7. The tail also weakened rapidly upon cooling the sample, implying its basic thermally activated nature. The shape of the spectrum as well as its temperature dependence were qualitatively well reproduced by quantum chemical calculations involving the pigment intramolecular vibrational modes, their overtones, and pairwise combination modes, but no intermolecular/solvent modes. A similar tail was observed earlier in the case of bacteriochlorophyll a, suggesting generality of this phenomenon. Long vibronic red tails are, thus, expected to exist in all pigments of light-harvesting relevance at physiological temperatures.

State-Targeted Energy Projection: A Simple and Robust Approach to Orbital Relaxation of Non-Aufbau Self-Consistent Field Solutions.

Orbital optimization is crucial when using a non-Aufbau Slater determinant that involves promotion of an electron from a (nominally) occupied molecular orbital to an unoccupied one, or else ionization from a molecular orbital that lies below the highest occupied frontier molecular orbital. However, orbital relaxation of a non-Aufbau determinant risks "variational collapse" back to the Aufbau solution of the self-consistent field (SCF) equations. Algorithms such as the maximum overlap method (MOM) that are designed to avoid this collapse are not guaranteed to work, and more robust alternatives increase the cost per SCF iteration. Here, we introduce an alternative procedure called state-targeted energy projection (STEP) that is based on level shifting and is identical in cost to a normal SCF procedure, yet converges in numerous cases where MOM suffers variational collapse. Benchmark calculations on small-molecule reference data suggest that ΔSCF calculations based on STEP are an accurate way to compute both ionization and excitation energies, including core-level ionization and excited states with significant double-excitation character. For the molecule 2,4,6-trifluoroborazine, ΔSCF calculations based on STEP afford excellent agreement with experiment for both vertical and adiabatic ionization energies, the latter requiring geometry optimization of a non-Aufbau valence hole. Semiquantitative agreement with experiment is obtained for the absorption spectrum of chlorophyll a. Finally, the importance of asymptotic exchange and correlation is illustrated by application to Rydberg states using spin-scaled Møller-Plesset perturbation theory with a non-Aufbau reference determinant. Together, these results suggest that STEP offers a reliable and affordable alternative to the MOM procedure for determining non-Aufbau solutions of the SCF equations.

Ba3Y2WO9:Mn4+: A near-UV and yellow-green light excited red phosphor for greenhouse cultivation

A novel Mn4+-activated Ba3Y2WO9 phosphor of double perovskite structure has been prepared via high-temperature solid-state reaction method. The phosphor can emit red emission located at ～692 nm, which greatly overlaps with the absorption spectra of chlorophyll and phytochrome in the red light range. the intensest excitation band of the phosphor originating in the O2−→Mn4+ charge transfer and the 4A2g→4T1g of Mn4+ centres at ～367 nm, while the sub intense excitation band formed by 4A2g→4T2g transition is located in the yellow-green light region (～535 nm). The excitation and emission performance of the phosphor indicates its potential application in light-conversion film/glass for greenhouse cultivation since it can convert not only UV but also yellow-green light into red emission. The optimal doping concentration of Mn4+in the Ba3Y2WO9 host is 0.3 mol%, beyond which energy transfer between Mn4+ ions based on d-d interaction results in fluorescence quenching. Besides, the crystal field strength and thermal stability of the sample are also discussed.