Green Gap Research Articles

Laser‐Driven High‐Brightness Green Light for Underwater Wireless Optical Communication

AbstractGreen light is generally used as the transmitter of underwater wireless optical communication (UWOC) system, but the currently available light‐emitting diode (LED)‐based green light has a poor luminous flux density (i.e., low brightness) and a low wall‐plug efficiency (WPE), known as the “green gap”. In this work, it is proposed to produce the laser‐driven green light by using blue laser diodes to pump the narrow‐band green‐emitting β‐Sialon phosphor‐in‐glass (PiG) film. The dominant wavelength of the laser‐driven green light can be tuned in the range of ≈520–540 nm, required for UWOC, by controlling the phosphor content at ≈60–80% and the film thickness at ≈150–185 µm. By introducing highly reflective TiO2 into the PiG film, the laser‐driven green light exhibits a maximum luminous flux density of 1260 lm mm−2 under blue laser excitation with a power density of 15.49 W mm−2. For UWOC application, the green light is demonstrated to have a modulation bandwidth of 1.76 MHz, a high WPE of 8.7%, and a long transmission distance of ≈61.6 m. This work suggests that the laser‐driven high‐brightness green light will be a promising light source for UWOC.

Enhancing Green Finance for Inclusive Green Growth: A Systematic Approach

Recently, green financing has become a popular technique for dealing with environmental issues. However, whether green financing is effective in addressing current global environmental issues remains to be seen since the green investment gap has been discovered to be rather sizable, with no certainty regarding how to fill it. The purpose of this study was to systematically analyze green finance in all of its forms, instruments, and measurements. Herein, we highlighted overall research trends in an effort to enhance green finance for inclusive green investment, as well as examined the progress needed to fill the green finance gap. This study also provides information on which authors, countries, publishers, and journals are contributing most to green finance. The methodological approach used in many reviewed papers was determined as a benchmark for those authors interested in green finance. Moreover, this study critically analyzes and summarizes 146 relevant studies. The results of our review study imply that the green financing gap is frequently observed because of low finance levels, poor green project selection/management, risk and return trade-off, and a lack of analytical tools and expertise in identifying and assessing green project risks. More specifically, regulatory issues have been observed as the main challenge in enhancing green finance. Therefore, we propose further studies to be conducted on how to enhance green finance for green investment that could deliberately affect green growth. Simultaneously, we noted what incentives could initiate private investors to make green investments, and what additional green financing methods should be introduced to fill the financing gap. Finally, this study seeks to have an impact in assisting future studies to consider the status of each country in terms of green finance mobilization and capital contribution by sharing the specific experience of that country and what lessons could be learned from that country.

Sustainable lifestyles, eating out habits and the green gap: a study of food waste segments

PurposeThis paper aims to identify Australian consumer segments based on sustainable lifestyles and attitudes towards food waste and model the factors (socio-demographic, attitudinal and lifestyle) contributing to different levels of food waste.Design/methodology/approachThis study uses a face-to-face survey of 334 respondents. Principal component analysis (PCA) is used to identify consumer segments, and econometric analysis is used to model the factors contributing to different levels of food waste.FindingsA total of six lifestyle segments are identified: the freshness lovers, the vegetarian and organic food lovers, the recycle/reuse advocates, the waste-conscious consumers, the label-conscious/sensory consumer and the food waste defenders. This research distinguishes between low and medium levels of food waste based on marginal effects analysis. At low levels of food waste, consumers who worry about the food waste cost, making efforts to reduce food waste are less likely to waste food. Affluent consumers, who claim to be waste conscious, have young children and frequently eat outside, are more likely to waste food than others, lying in the medium waste group.Originality/valueAustralia, like many other countries, has high levels of food waste and despite policy efforts, curbing household food waste remains a challenge. In addition, there are limited food waste studies that focus on consumers who practice sustainable lifestyles. The current paper contributes to the market segmentation literature and has several implications for food policy and practice.

Comparative investigation into polarization field-dependent internal quantum efficiency of semipolar InGaN green light-emitting diodes: A strategy to mitigate green gap phenomenon

Semipolar InGaN-made green light-emitting diodes (LEDs) have sparked tremendous interest within the photonics community in recent past as advantageous replacements for already operable polar (0001)-oriented LEDs due to reduction in efficiency droop and related green gap phenomenon. Nevertheless, any theoretical investigation in order to compare internal quantum efficiency (IQE); output power and 3 dB bandwidth (BW) within non-c-plane-oriented InGaN green LEDs is innately unavailable. This study intends to describe the consequence of strain-induced polarization field on aforesaid major optical and electronic characteristics of In0.29Ga0.71N/GaN green LED along semipolar (101̅2), (112̅2), (101̅1), (202̅1), (303̅1̅), (202̅1̅) and (101̅1̅) crystal orientations by introducing modified ABC model which involves the contribution from phase-space filling (PSF) and carrier drift leakage. Our numerical investigation illustrates that best IQE, droop ratio, light emission spectra, output power and I-V profile can be obtained from (112̅2)-oriented InGaN green LED due to inconsiderable appearance of intrinsic plus lattice-mismatch induced piezoelectric polarization charge. 3 dB BW and differential carrier lifetime (DLT) is also shown to be superior for this green LED structure. In addition with these, the evidence noticed from verification of external quantum efficiency (EQE) with previous experimental reports on semipolar (112̅2) InGaN green LEDs indicates reasonable accuracy of our theoretical approach.

Leveraging Blockchain Technology and Tokenizing Green Assets to Fill the Green Finance Gap

Clean energy projects have difficulties accessing finance. The transition to clean energy and accelerating investments in green projects require a game-changing approach, groundbreaking infrastructure, and pioneering green financing strategies. This article discusses the potential of blockchain technology in filling the green investment gap. Use cases related to the application of blockchain in green projects are analyzed. Blockchain technology can provide security, transparency, auditability, and traceability and help fill the green finance gap.

Efficient Green Light Acclimation of the Green Algae Picochlorum sp. Triggering Geranylgeranylated Chlorophylls.

In analogy to higher plants, eukaryotic microalgae are thought to be incapable of utilizing green light for growth, due to the “green gap” in the absorbance profiles of their photosynthetic pigments. This study demonstrates, that the marine chlorophyte Picochlorum sp. is able to grow efficiently under green light emitting diode (LED) illumination. Picochlorum sp. growth and pigment profiles under blue, red, green and white LED illumination (light intensity: 50–200 μmol m−2 s−1) in bottom-lightened shake flask cultures were evaluated. Green light-treated cultures showed a prolonged initial growth lag phase of one to 2 days, which was subsequently compensated to obtain comparable biomass yields to red and white light controls (approx. 0.8 gDW L−1). Interestingly, growth and final biomass yields of the green light-treated sample were higher than under blue light with equivalent illumination energies. Further, pigment analysis indicated, that during green light illumination, Picochlorum sp. formed unknown pigments (X1-X4). Pigment concentrations increased with illumination intensity and were most abundant during the exponential growth phase. Mass spectrometry and nuclear magnetic resonance data indicated, that pigments X1-X2 and X3-X4 are derivatives of chlorophyll b and a, which harbor C=C bonds in the phytol side chain similar to geranylgeranylated chlorophylls. Thus, for the first time, the natural accumulation of large pools (approx. 12 mg gDW −1) of chlorophyll intermediates with incomplete hydrogenation of their phytyl chains is demonstrated for algae under monochromatic green light (Peak λ 510 nm, full width at half maximum 91 nm). The ability to utilize green light offers competitive advantages for enhancing biomass production, particularly under conditions of dense cultures, long light pathways and high light intensity. Green light acclimation for an eukaryotic microalgae in conjunction with the formation of new aberrant geranylgeranylated chlorophylls and high efficiency of growth rates are novel for eukaryotic microalgae. Illumination with green light could enhance productivity in industrial processes and trigger the formation of new metabolites–thus, underlying mechanisms require further investigation.

Organic food purchase decisions from a context-based behavioral reasoning approach

While the burgeoning development of organic foods has received great interest from academicians, the green gap has been posing challenges to the understanding of the inconsistency between consumers' actions and their positive intentions towards organic foods. The latest marketing literature has pointed to the potential of the cognitive and reasoning process taking into account context-specificity as the answer to the problem. Applying the novel Behavioral Reasoning Theory, this study sets out to bridge this gap by providing insights into the context-based reasoning process of Vietnamese consumers. PLS-SEM method was employed to test the proposed hypotheses between values, reasons, attitudes, behavioral intention, and actual purchase behavior among 300 consumers from two big cities (i.e., Hanoi and Ho Chi Minh) in Vietnam. The mediation analysis was conducted for reasons and attitudes. The model was also extended using trust and knowledge factors. Overall, the results suggested the strong cognitive routes originated from values onto reasons and attitudes, whereas attitudes and reasons (for and against) positively influenced purchase intentions. Additionally, the mediational effects of both reasons and attitudes were not established. Trust was found strengthening reasons for and attitudes while mitigating reasons against. Consumers’ knowledge rendered impacts on intentions but not attitudes. Useful implications for academicians, marketers, and policymakers were also discussed.

Numerical study on photoelectric properties of semi-polar 101̄1 green InGaN light-emitting diodes with quaternary AlInGaN quantum barriers

Semi-polar 101̄1 green InGaN light-emitting diodes with different quantum barrier materials were numerically investigated by considering the In composition fluctuation model. For the green light-emitting diode using quaternary Al0.05In0.1Ga0.85N quantum barriers with low Al content, the electric field was reduced, the carrier distribution was appropriately modified, and the efficiency droop was significantly alleviated. In particular, the band pulldown was relieved, and the Fermi levels were flatter, which elevated the electron confinement and decreased the hole injection potential barrier, further promoting hole transport. Moreover, the carrier distribution was more homogeneous and no longer concentrated in the last quantum well, resulting in a reduced nonradiative recombination rate and minimal turn-on voltage. Finally, the internal quantum efficiency was further enhanced by increasing the radiative recombination and thus the efficiency decreased by only 9.1% at a current density of 1000 A/cm2. The proposed structure using quaternary Al0.05In0.1Ga0.85N with low Al molar fraction as a quantum barrier showed great potential for overcoming the “green gap” problem and application in high-power scenarios.

Superior Optoelectronic Performance of N-Polar GaN LED to Ga-Polar Counterpart in the “Green Gap” Range

The low luminous efficiency of indium gallium nitride (InGaN) light-emitting diodes (LED) in the “green gap” range has been a long unsettled issue confounding the researchers. One of the main obstacles comes from the intrinsic polarization field in the incumbent Ga-polar LEDs (Ga-LEDs), where the polarization field will bend the energy band thus reducing the radiative recombination efficiency. The scenario will become different when we reverse the polarization field with the adoption of N-polar GaN, which should be a promising candidate to obtain LEDs with high luminous efficiency in the “green gap” range. In this study, the optical and electronic performances of InGaN LEDs in the “green gap” range with N- and Ga-polar have been numerically investigated. The results demonstrate that the light-output power of N-polar LED (N-LED) is ~1.69-fold higher than that of Ga-LED at a current density of 1250 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , thus leading to a significantly improved internal quantum efficiency. Meanwhile, the turn-on voltage of N-LED is lowered by ~17.3% compared to that of Ga-LED. As revealed by the energy band diagram, the superior optoelectronic performance of N-LED is mainly attributed to the stronger carrier confinement in the active region and the lower carrier injection barriers. This study suggests the prospective realization of high luminous efficiency InGaN LEDs in the “green gap” range by the implementation of N-LEDs.

Shifting LED emission from blue to the green gap spectral range using In0.12Ga0.88N relaxed templates

In y Ga 1-y N templates are grown with y ≤ 13.5% and a few nm surface roughness . These templates are used successfully to address two of the main issues facing long wavelength emitting LEDs, mainly the low growth temperature and high values of strain in the quantum wells (QWs). In this work, three LED structures are investigated: the first is a blue LED grown on GaN, the second and third are green LEDs grown on relaxed In y Ga 1-y N templates with y of about 10% and 12%, respectively. The same multiple quantum wells (MQWs) were used in the three LED structures, with the same well width, barrier width, and growth temperature. The reduced strain in the QWs due to the use of InGaN templates enhances the indium incorporation rate in the QWs. Red shift in emission wavelength of about 100 nm, from 470 nm to 570 nm, was achieved, at low injection current. Optical output power and external quantum efficiency (EQE) measurements showed that at high level of current injection, performance of the blue LED is about twice of the green emitting LEDs on InGaN templates. The current results indicate the potential of the InGaN template approach, with high values of y , in addressing problems facing long wavelength InGaN LEDs. • Relaxed InGaN templates are used to shift blue LED emission from blue to the green gap spectral range. • Indium content>10% shows surface roughness of few nanometers and pit density in the 10 7 cm −2 to the mid 10 8 cm −2 range. • Performance of the blue the blue LED on GaN is about twice that of green LED on InGaN templates.

Signalling compliance: an explanation of the intermittent green policy implementation gap in China

ABSTRACT The existence of the green policy implementation gap in China has aroused widespread concern, and is frequently explained with officials’ characteristics, problematic institutions, and citizens’ participation. However, few studies have noticed the intermittence of the gap. By coding six media signals and 394 documents issued by the central government (2000–2015) from 27 items in dimensions of credibility/reliability, intensity, and clarity according to the signalling theory, causes of the intermittence were explored. I found that central signals are the driving force. Document signals work better than media signals, particularly in Hu Jintao’s era. Documents’ credible commitments, threats, legal effects, issuing departments, wording intensity, clear definition of departments and society’s responsibilities, and regulation targets can significantly stimulate local governments’ environmental regulation behaviours, especially in eastern China. In Xi Jinping’s era, credible commitments and environmental campaigns’ impacts are higher. The paper demonstrates how, where and when China’s model of environmental authoritarianism is effective.

Highlighting Theodor W. Engelmann's “Farbe und Assimilation” [Color and Assimilation

AbstractIn 1883, Theodor Wilhelm Engelmann, a German scientist, wrote his essay “color and assimilation” (Ger.: “Farbe und Assimilation”) describing the state of the art in photosynthesis research, his recent findings, and further assumptions based upon his presented results. Nearly 140 years later, many of his assumptions were proven correct. By his still well‐known bacteria experiments using aerotactic, heterotrophic bacteria, he identified the chloroplasts as the location in which photosynthesis and oxygen production takes place. Furthermore, by evaluating the effects of different light spectra, he constructed the first action spectra that demonstrated the implication of the “green gap” of chlorophylls. He further posited that accessory photosynthetic pigments existed to extend the absorption range of chlorophyll. Although infrequently cited, his work was foundational for current ecological research of the vertical appearance of algae species within the underwater gradient in light spectrum due to specific harvesting of different light spectra, hence complementary chromatic adaptation of communities. This short retrospective highlights this piece of literature that represents an early step toward our current understanding of ecological competition for light spectra.

β‐SiAlON:Eu2+ Phosphor‐in‐Glass Film: An Efficient Laser‐Driven Color Converter for High‐Brightness Wide‐Color‐Gamut Projection Displays

AbstractThe green‐emissive laser phosphor is urgently demanded for projection displays to compensate the “Green Gap.” Herein, the well‐known β‐SiAlON:Eu2+ with admirable luminescent feature is incorporated into robust silicate glass matrix, cosintered on sapphire plate, and then constructed into “phosphor wheel,” succeeding in retaining excellent green‐emissive performance and meanwhile relieving the luminescence droop at high pumping density of blue laser. Probing the local effect of laser–matter interaction reveals that the luminescence saturation is majorly determined by thermal quenching, but the influence of intensity quenching cannot be ignored. Systematical works are performed to optimize glass composition, cosintering procedure, sample parameters, and optical path, turning out the maximal quantum efficiency of 60%, thermal conductivity of 9.5 W m−1 K−1, and high saturation threshold far beyond 22 W mm−2. In a proof‐of‐concept experiment, accompanied with red laser diode, the constructed light engine yields a high brightness with luminous flux of 1310 lm (luminance of 880 Mcd m−2), a low étendue of ≈1.5 mm2, and a wide color gamut of 112.5% National Television System Committee (NTSC), demonstrating the composite material as an efficient laser‐driven color converter for projection displays.

Multimicroscopy of cross-section zincblende GaN LED heterostructure

Zincblende GaN has the potential to bridge the “green gap” due to the absence of internal electric fields with respect to wurtzite GaN. However, at present, the quality of zincblende GaN light emitting diodes (LEDs) is not yet sufficient for useful efficient green devices. One of the major challenges is the poor spectral purity of the emitted light. A multimicroscopy approach, combining scanning electron microscopy-cathodoluminescence (SEM-CL), scanning transmission electron microscopy (STEM), and scanning electron diffraction (SED), is applied on a single feature to enable cross correlation between techniques and to investigate the possible causes for the broad optical emission of a zincblende GaN LED structure. This investigation demonstrates that SEM-CL on a site-specific TEM cross section prepared by focused ion beam (FIB) microscope can provide access to nanoscale light emission variations that can be directly related to structural differences seen in STEM. We demonstrate that the general large quantum well (QW) emission peak width relates to quantum well thickness and In content fluctuations. Multiple low-energy QW emission peaks are found to be linked with stacking fault bunches that intersect the QWs. Splitting of the QW emission peak is also found to be caused by the formation of wurtzite-phase inclusions associated with twins formed within the zincblende matrix. Our characterization also illustrates the quantum well structure within such wurtzite inclusions and their impact on the optical emission.

Modelling the macroeconomics of a ‘closing the green finance gap’ scenario for an energy transition

Reaching the UK net-zero emissions target translates into substantial investment requirements into low-carbon energy infrastructure. However, investors are currently not investing sufficiently in renewable energy capacity, leading to the so-called green finance gap. Current energy-economy models generally do not reveal the macroeconomic implications of policies aimed at scaling-up green finance for energy transitions. In the light of this background, we extend the energy-economy Green Investment Barrier Model with the insights from a systematic literature review to investigate the macroeconomic implications of a policy scenario designed to close the green finance gap in combination with and without a scenario to decarbonise the power sector. We also compare the achieved results with studies focusing on a similar research question. We find that the closing the green finance gap policy scenario alongside a low-carbon power scenario leads to the co-benefits of lower power system costs and unemployment, and increases in GDP.

Monolithic Multi‐Color Tunable Inorganic Light‐Emitting Diodes

AbstractInorganic light‐emitting diodes (LEDs) possess exceptional advantages for achieving wide wavelength emission ranges. However, certain material limitations should be overcome to alleviate the green gap between InGaN and AlInGaP‐based LEDs. In this study, monolithic red, green, and bluish‐green emissions are achieved by exploiting the blueshift phenomenon, caused by the band‐filling and piezoelectric screening effects. Different‐sized LEDs are designed to control the injection current density on the same wafer. The smaller the size of the LED, the shorter the emission wavelength, resulting in multi‐color emission (from red to bluish‐green). As a result, red, green, and white emissions are individually and simultaneously obtained using dichromatic LED systems, comprising three red and one green LED cell. In addition, a wide range of visible light colors are achieved by adjusting the size of the LEDs and the applies injection current.

Green Skills Gap in the Bulgarian Tourism Industry

Green skills are crucial for the sustainable development of tourism and hospitality companies and significantly contribute to their overall performance. This study explores the green skills gaps in...

Understanding the green total factor energy efficiency gap between regional manufacturing—insight from infrastructure development

Infrastructure development and energy efficiency improvement are crucial to the high-quality transformation of the economy. However, little literature discusses how infrastructure development affects the energy efficiency gap between regional manufacturing. This paper estimates the per capita capital stock of economic infrastructure and the green total factor energy efficiency of China's manufacturing industry. Unlike the prior grouping according to geographical location or other standards, this paper conducts a data-driven clustering method and convergence analysis on energy efficiency. Thirty provinces eventually converge into four clubs, and the gaps in energy efficiency between various clubs are found to persist. The results of the panel-ordered Probit model indicate that infrastructure development can reduce regional discrepancies in manufacturing's green total factor energy efficiency. This effect is heterogeneous in transportation infrastructure and power infrastructure. As time goes on, the marginal effect of infrastructure diminishes. Moreover, the established infrastructure reduces the regional disparities in energy efficiency, while the infrastructure under construction instead widens the gap. Some relevant policy recommendations are provided for future infrastructure planning and green development strategy based on the conclusions.

Watt-Level Visible Continuous-Wave Upconversion Fiber Lasers toward the “Green Gap” Wavelengths of 535–553 nm

The development of visible fiber lasers toward increasing power and variety has facilitated their usage in a rapidly growing number of scientific and industrial applications. Until now, holes in the visible spectral region have remained difficult or expensive to fill. Green laser oscillation in Ho3+ active fibers has contributed to bridging the so-called “green gap” between readily accessible spectral ranges, which is difficult to access with conventional semiconductor laser sources. However, green fiber lasers are limited in power because of the lack of high-brightness pump sources. Their wavelength tuning capability is also bottlenecked at short emission wavelengths due to the strong signal reabsorption. In this study, we developed a means of continuously tunable laser operation at the true-green wavelength of 535–553 nm. In a free-running laser operation, an output power up to 0.98 W was achieved at a center wavelength of 543.1 nm, yielding a Gaussian-like beam. This represents the highest power level demonstrated to date from a visible Ho3+-doped fiber laser. The results enable a new class of broadband green tunable fiber lasers with a power level on the order of watts and beyond, filling in the “green gap”.

Why is green consumption easier said than done? Exploring the green consumption attitude-intention gap in China with behavioral reasoning theory

Abstract Many consumers have shown positive attitudes towards green consumption; however, these attitudes do not necessarily translate into intentions or behaviors. To analyze this attitude-intention and hence behavior gap, this paper employs behavioral reasoning theory which extends the traditional theory of planned behavior by including context-specific reasons, in addition to values and global motives as possible determinants of intentions and behaviors. This study collected first-hand data by conducting a face-to-face survey with 839 Chinese consumers from four cities in Jiangsu Province and eight cities in Anhui Province, and applies structural equation modeling for data analysis. The results indicate that reasons for green consumption affect intentions only indirectly through attitudes, while reasons against green consumption impact intentions in a direct way, bypassing attitudes. In other words, reasons against green consumption impede intentions, despite positive attitudes. At the same time, both types of reasons are influenced by environmental values. To bridge the attitude-intention gap, we propose measures that the governments and businesses can take to raise the environmental values of consumers, and reduce their “reasons against” and increase their “reasons for” green consumption.