Academic literature on the topic 'Nitride RED phosphor'

Multiternary nitride and oxynitride compounds doped with rare earth ions, such as Eu2+ and Ce3+ have been enthusiastically applied as various phosphors to white LED. New red and green phosphors, CaAlSiN3:Eu and Ba3Si6O12N2:Eu, have been successfully synthesized, recently. The red phosphor has intense emission around 650 nm under two different irradiations at 405 and 455 nm from blue- and near UV-LED chips, respectively; while strong emission is observed around 520 nm from the green phosphor. Both phosphors also show small thermal quenching over the temperatures up to 150 °C. In addition, both LaSi3N5:Ce and La3Si8O4N11:Ce in lanthanum silicon nitride and oxynitride were examined as candidates for a blue phosphor in white LED with near UV-LED chip.

Solid-state lighting (SSL) is emerging as a highly competent field and a possible alternative to existing lighting technologies. Development of a suitable phosphor is an important aspect of SSL. The aim of this review is to summarize status of Inorganic Phosphors towards SSL applications. Various examples have been taken from oxide, fluoride, nitride, sulfide and phosphate based host lattices. The important concepts like CIE coordinates and Color Correlated Temperature (CCT) will also be discussed. The sections encompasses of red, blue and green light emitting phosphors. The white light emitting phosphors will also be discussed in details.

The red persistent luminescence and the photostimulable luminescence in the nitride SrLiAl₃N₄:Eu²⁺ are reported, and the mechanism are discussed on the basis of the HRBE diagram.

Narrow band deep-red emission SrLiAl₃N₄:Eu²⁺ phosphor was effectively synthesized using complex nitride Sr₃Al₂N₄ and Li₃AlN₂ as raw materials. The phosphor exhibited strong deep-red emission peaking at 654 nm under excitation at 450 nm.

Red-emitting BCNO phosphor has been synthesized by a microwave-assisted solid state reaction using a low-cost boric acid, urea and polyethylene glycol (PEG-20k) as the starting materials. The effects of reaction parameters: temperature, carbon and nitrogen content on material composition and photoluminescence properties were investigated. Nearly multi-phase hexagonal boron nitride, boron oxide, boron carbide and carbon graphite was observed, indicating the BCNO were successfully synthesized. The photoluminescence spectra of the phosphor excited by a UV light (365 nm) showed a broad emission band at 460 - 620 nm.

A near infrared (NIR) persistent luminescent Ba[Mg₂Al₂N₄]:Eu²⁺–Tm³⁺ phosphor chargeable by red light was prepared via a solid state reaction from all-nitride starting materials.

En 2008, pour la première fois toutes les fonctions d’éclairage avant d’un véhicule sont entièrement à LEDs. Cette source de lumière a ouvert l'âge d'or de l'éclairage automobile par la basse consommation électrique, l’efficacité, la fiabilité, la haute luminosité, la compacité, ainsi que la rentabilité. Ces qualités lui ont permis de gagner la majorité des parts de marché dans l’automobile.La miniaturisation de la LED a permis la pixellisation du faisceau lumineux. Cela améliore davantage la sécurité routière. En effet, éclairer la route sans éblouir les autres usagers est devenu possible avec cette technologie. En outre, le besoin d'éclairage évolue avec l'arrivée de la voiture autonome. C’est alors que les technologies des LEDs pixélisées représentent des perspectives dans le domaine de l’éclairage pour les capteurs, et même dans la communication par la projection des pictogrammes et/ou l’écriture sur la route. Un second axe de recherche sera traité dans cette thèse. Il consiste à étudier les LEDs rouges avec luminophore pour les fonctions de signalisation arrière en automobile.De nouveaux mécanismes de défaillances vont faire surface, dû à ces nouveaux profils de mission et les nouvelles techniques de fabrication des LEDs immatures. Un besoin critique d’une démarche scientifique pour définir et exécuter un plan de tests et des caractérisations électriques, optiques, physiques et thermiques de ces nouvelles technologies.Les objectifs principaux de ces travaux de thèse seront de développer des nouvelles méthodes, des nouveaux bancs de caractérisations Opto-Électro-Thermiques et d’investiguer les modes et les mécanismes de défaillances liés aux processus de fabrication, géométries, matériaux de composition et aux nouveaux profils de mission des systèmes d'éclairage
In 2008, all front lighting functions of a vehicle are based on full LEDs for the first time. This light source opened the golden age of automotive lighting through low power consumption, efficiency, reliability, high brightness, compactness, as well as cost efficiency. These qualities have enabled it to gain the majority of the automotive market share.The miniaturization of the LED made possible the light beam pixelization. This further improves road safety. Indeed, lighting the road without glairing other users has become possible with this technology. In addition, lighting needs are changing with the arrival of the autonomous car. This is when pixelated LED technologies represent prospects in the field of lighting for sensors, and even in communication through the projection of pictograms and / or writing on the road.A second research axis will be dealt with in this thesis. It consists of studying red LEDs with phosphor for automotive rear signaling functions.New failure mechanisms will emerge, due to these new mission profiles and new techniques for manufacturing immature LEDs. A critical need for a scientific approach to define and execute a test plan and electrical, optical, physical and thermal characterizations of these new technologies.The main objectives of this thesis will be to develop new methods, new Opto-Electro-Thermal benchs’ characterizations and to investigate the modes of failure mechanisms related to manufacturing processes, geometries, composition materials and to new lighting systems mission profiles

Throughout Central Florida surface water and ground water are decreasing in quantity and quality in part because of excess Nitrate and Phosphorus nutrients. Stormwater runoff serves as a medium for transport of Nitrate and Phosphorus to surface water and ground water. The goal of this experiment is assess the Nitrate and Phosphorus removal in stormwater using select media. The results of a literature search, batch test experimentation and column test experimentation are used to determine an optimal media blend that may be implemented in detention ponds to reduce Nitrate and Phosphorus. The extensive literature search revealed 32 different media that may be used to remove Nitrate and Phosphorus. Each potential media was qualitatively and quantitatively evaluated based on 5 criteria: 1) relevance, 2) permeability, 3) cost, 4) availability in Florida, and 5) additional environmental benefit. The top 7 performing media: Florida peat, sandy loam, woodchips, crushed oyster shell; crushed limestone, tire crumb and sawdust were selected for batch test experimentation. The aerobic conditions in batch test experimentation prohibited the growth of denitrifying bacteria, therefore media mixes were selected for column test experimentation based on Ammonia and Orthophosphate concentrations. Batch test experimentation showed the most effective media to be 50% sand, 30% tire crumb, 20% sawdust by weight (media mix 1) and 50% sand, 25% sawdust, 15% tire crumb, 10% limestone by weight (media mix 2). Media mix 1, media mix 2 and a control are tested in column test experimentation, where the control is site soil from Hunters Trace development in Ocala, Florida. Column test experimentation models a dry detention pond where water passes through a 48 inch unsaturated zone then a 48 inch saturated zone. To test Nitrate and Orthophosphate removal potential, pond water augmented with Nitrate (0.38, 1.26, 2.5 mg/L NO3-N) and Orthophosphate (0.125, 0.361, 0.785 mg/L PO4-P) was pumped into the columns. Media mix 1 and media mix 2 outperformed the control in both Nitrate and Orthophosphate removal. Media mix 1 and media mix 2 had Nitrate removal efficiencies ranging from 60% to 99% and the control had Nitrate removal efficiencies ranging from 38%-80%. Media mix 1 and media mix 2 averaged Orthophosphate removal efficiencies ranging from approximately 42% to 67%. For every run in every influent Orthophosphate concentration the saturated control added Orthophosphate to the water. The Nitrate and Orthophosphate removal performances for media mix 1 and media mix 2 could not be directly compared because of different influent saturated nutrient concentrations.
M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engr MSEnvE

Elevated concentrations of nutrients, particularly nitrate, in groundwater and springs in Florida are a growing resource management concern. Stormwater infiltration basins, which are a common stormwater management practice in the well-drained karst terrain areas of Florida, are a potentially important source of nutrients to the groundwater system because stormwater exits the basin by only evaporation or infiltration. To better understand the biogeochemical processes integrating stormwater infiltration impacts on groundwater resources in a field-scale setting, a combination of hydrologic, soil chemistry, water chemistry, dissolved and soil gas, isotope, and microbiological data was collected from 2007 through 2010 at two stormwater infiltration basins receiving runoff from predominantly residential watersheds in north-central Florida. Substantially different biogeochemical processes affecting nitrogen fate and transport were observed beneath the two stormwater infiltration basins. Differences are related to soil textural properties that deeply link hydroclimatic conditions with soil moisture variations in a humid, subtropical climate. During 2008, shallow groundwater beneath the basin with predominantly clayey soils (median 41% silt+clay content) exhibited decreases in dissolved oxygen from 3.8 to 0.1 mg/L and decreases in nitrate-nitrogen from 2.7 mg/L to less than 0.016 mg/L, followed by manganese and iron reduction, sulfate reduction, and methanogenesis. In contrast, beneath the basin with predominantly sandy soils (median 2% silt+clay content), aerobic conditions persisted from 2007 through 2009 (dissolved oxygen of 5.0–7.8 mg/L), resulting in nitrate-nitrogen of 1.3–3.3 mg/L in shallow groundwater. Soil extractable nitrate-nitrogen was significantly lower and the copper-containing nitrite reductase gene density was significantly higher beneath the clayey basin. Differences in moisture retention capacity between fine- and coarse-textured soils resulted in median volumetric gas-phase contents of 0.04 beneath the clayey basin and 0.19 beneath the sandy basin, inhibiting surface/subsurface oxygen exchange beneath the clayey basin. Subsurface biogeochemical processes at the clayey stormwater infiltration basin were further analyzed to better understand the effects of the highly variable hydrologic conditions common in humid, subtropical climates. Cyclic variations in biogeochemical processes generally coincided with wet and dry hydroclimatic conditions. Oxidizing conditions in the subsurface persisted for about one month or less at the beginning of wet periods with dissolved oxygen and nitrate showing similar temporal patterns. Reducing conditions in the subsurface evolved during prolonged flooding of the basin. At about the same time oxygen and nitrate reduction concluded, manganese, iron, and sulfate reduction began, with the onset of methanogenesis one month later. Reducing conditions persisted up to six months, continuing into subsequent dry periods until the next major oxidizing infiltration event. Evidence of denitrification in shallow groundwater at the site is supported by median nitrate-nitrogen less than 0.016 mg/L, excess nitrogen gas up to 3 mg/L progressively enriched in delta-15N during prolonged basin flooding, and isotopically heavy delta-15N and delta-18O of nitrate (up to 25 and 15 per mil, respectively). Isotopic enrichment of newly infiltrated stormwater suggests denitrification was partially completed within two days. Soil and water chemistry data suggest a biogeochemically active zone exists in the upper 1.4 m of soil, where organic carbon was the likely electron donor supplied by organic matter in soil solids or dissolved in infiltrating stormwater. The cyclic nature of reducing conditions effectively controlled the nitrogen cycle, switching nitrogen fate beneath the basin from nitrate leaching to reduction in the shallow saturated zone. Soil beneath the sandy stormwater infiltration basin was amended using biosorption activated media (BAM) to study the effectiveness of this technology in reducing inputs of nitrogen and phosphorus to groundwater. The functionalized soil amendment BAM consists of a 1.0:1.9:4.1 mixture (by volume) of tire crumb (to increase sorption capacity), silt and clay (to increase soil moisture retention), and sand (to promote sufficient infiltration), which was applied to develop an innovative best management practice (BMP) utilizing nutrient reduction and flood control sub-basins. Construction and materials costs, excluding profit and permit fees, for the innovative BMP were about $US 65 per square meter of basin bottom. Comparison of nitrate/chloride ratios for the shallow groundwater indicate that prior to using BAM, nitrate concentrations were substantially influenced by nitrification or variations in nitrate input. In contrast, for the new basin utilizing BAM, nitrate/chloride ratios indicate minor nitrification and nitrate losses with the exception of one summer sample that indicated a 45% loss. Biogeochemical indicators (denitrifier activity derived from real-time polymerase chain reaction and variations in major ions, nutrients, dissolved and soil gases, and stable isotopes) suggest nitrate losses are primarily attributable to denitrification, whereas dissimilatory nitrate reduction to ammonium and plant uptake are minor processes. Denitrification was likely occurring intermittently in anoxic microsites in the unsaturated zone, which was enhanced by increased soil moisture within the BAM layer and resultant reductions in surface/subsurface oxygen exchange that produced conditions conducive to increased denitrifier activity. Concentrations of total dissolved phosphorus and orthophosphate were reduced by more than 70% in unsaturated zone soil water, with the largest decreases in the BAM layer where sorption was the most likely mechanism for removal. Post-BAM orthophosphate/chloride ratios for shallow groundwater indicate predominantly minor increases and decreases in orthophosphate with the exception of one summer sample that indicated a 50% loss. Differences in nutrient variations between the unsaturated zone and shallow groundwater may be the result of the intensity and duration of nutrient removal processes and mixing ratios with water that had undergone little biogeochemical transformation. In order to quantify potential processes leading to observed nitrogen losses beneath the innovative BMP, an integrated infiltration basin–nitrogen reduction (IBNR) system dynamics model was developed. Based on two simulation periods, the IBNR model indicated denitrification accounted for a loss of about one-third of the total dissolved nitrogen mass inflow and was occurring predominantly in the BAM layer. The IBNR model results in combination with the field-based biogeochemical assessment demonstrated that the innovative BMP using the functionalized soil amendment BAM is a promising passive, economical, stormwater nutrient-treatment technology. Further field- and laboratory-scale research on the long-term sustainability of nutrient losses and further elucidation of causative physicochemical and biogeochemical mechanisms would contribute to improved BAM performance and green infrastructure development in the future.
ID: 031001572; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Ni-Bin Chang.; Title from PDF title page (viewed August 26, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 246-263).
Ph.D.
Doctorate
Civil, Environmental, and Construction Engineering
Engineering and Computer Science
Civil Engineering

博士
國立成功大學
化學工程學系
104
White light LED lighting is believed to replace the conventional lighting and becomes the next generation lighting device due to its advantages such as energy efficiency, long lifetime, compactness, environment friendliness and designable features. Phosphors are essential materials for the fabrication of the LED lighting devices and their properties significantly affect the performance of the devices. Among various types of phosphor, the type with red emission is considered to be the most urgent one to be developed for two main reasons: Its use can improve the color rendering of the currently commercialized LED lighting devices and conventional red phosphors suffer from poor thermal and chemical stability and low quantum efficiency. Recently, nitride phosphors have been discovered and shown to be ideal for application in LED lighting due to their superior properties such as high quantum efficiency, long wavelength (red) emission and high thermal and chemical stability. However, the methods that have been developed for synthesis of nitride phosphors mostly suffer from either severe synthesis conditions or involving the use of moisture or oxygen sensitive starting materials, resulting in high production costs and thus high market prices of the commercially available nitride phosphors, and limiting the application of the LED lighting devices. In the past few years, we developed a combustion synthesis method for nitride phosphors with advantages including simple and inexpensive equipment required, relatively low cost of the reactants, a fast reaction and short processing time, potential capability for mass production. Effects of N2 gas pressure and reactant compositions related to product yield and emission property will be discussed in this research.The research result reveals the that product yield, emission intensity and wavelength of CaAlSiN3:Eu2+ phosphor can be controlled via adjust the reactant compositions using thermal insulation apparatus. Moreover, effects of Ca content (in the reactant mixture) on the formation and the photoluminescence properties of CaAlSiN3:Eu2+ phosphor (CASIN) were investigated. The plate-like blue-green emission of AlN:Eu2+ phosphor, both of plate-like and bar-like orange-red emission of Ca-α-SiAlON:Eu2+ phosphor and plate-like ,bar-like and irregular-shaped (i.e., agglomerated fine particles) red emission of CaAlSiN3:Eu2+ phosphor can be synthesized at the same time with various Ca contents. The bar-like morphology of CaAlSiN3:Eu2+ seen to have stronger emission than the other two morphologies (i.e., plate-like and agglomerated fine particles of CaAlSiN3:Eu2+), The Ca and Eu contents (expressed as molar ratios) in the synthesized products were found to increase roughly with increasing Y but were both lower than the respective Ca and Eu contents in the reactant mixtures.The synthesized CaAlSiN3:Eu2+ phosphor absorbs light in the region of 220–600 nm and shows a broad band emission in the region of 500–800 nm under excited by the blue light (460 nm) and generates emission peaking at ~650 nm.

碩士
國立臺灣大學
化學研究所
106
The narrowband red-emitting phosphor SrLiAl3N4:Eu2+(SLA) with extraordinary structure and excellent luminous properties is regarded as a prospective red phosphor for white light-emitting diodes(WLEDs). The quality of the white-LED depends on the emission intensity and luminous efficacy of radiation (LER) of the component phosphor, which is, in turn, is related to the emission wavelength, and the bandwidth of the phosphor. As it is now, the emission efficiency of SLA is still not sufficient for the commercial application. Besides, to obtain the optimum luminous efficiency, the emission wavelength of the phosphor should be between 620-630 nm, while the emission wavelength of SLA phosphor is at 655 nm, where the human eyes’ sensitivity is low, and will lead to a decrease in LER. Thus, to obtain the high quality of WLED, improving the emission intensity and blue-shifting the emission wavelength of this phosphor are necessary. The properties of SLA was optimized by chemical substitution with using Ba3N2 as flux. By the addition of flux, the Morphology of the SLA phosphor was improved by smoother surfaces and larger particle sizes that reflected enhanced luminescence properties and stability in the high-temperature devices. By tuning the environment of the luminescence centers via chemical substitution, where the SLA host was modified by substitution of Ga in the Al site, the emission peak at 655 nm was successfully shifted to 630 nm, and enhanced its LER and efficiency up to 1.25 compared to SLA. The narrowband red-emitting SLA was prepared by using solid-state reaction under high pressure. The crystal structure information was investigated by X-ray diffractometer and refined by TOPAS. To describe the relationship between the crystal structure and its luminous properties, the photoluminescence and the temperature-dependent photoluminescence properties were analyzed. To investigate the environments of the luminescence centers, time-resolved emission spectra and decay times at low temperature were measured, and the ultra violet-visible-Near Infrared device was used to evaluate the feasibility of the fabrication into WLED device.

博士
國立臺灣大學
化學研究所
104
Traditional WLEDs are fabricated using blue chip and yellow phosphor to produce white light, with high efficiency but poor color rendering index (CRI) because of the lack of a red component. In this work, using chemical substitution and synthesis conditions on the basis red nitride phosphors, while theoretical discussion of their chemical properties. The light emission of Sr2Si5N8:Eu2+ at 620 nm, the orange light is ideal to red source. The properties of Sr2Si5N8:Eu2+ can be tailored by tuning the pressure, temperature, and sintering time in the basic sintering process. In the synthesis of Sr2Si5N8:Eu2+, Sr2Si5N8:Eu2+ was converted into SrSi6N8:Eu2+ during heating. CaAlSiN3: Eu2+ is also one of the highly stable material, which is located 650 nm. (Sr,Ca)AlSiN3:Eu2+, was developed through cation substitution and blue shift to 620 nm of peak position. Distortion of the lattice structure introduced adequate space and highly coordinated sites in the Sr/Eu centers for charge variation effect. Subsequently, typically arranged variations of the SiN¬4 and AlN4 clusters were formed in the lattice by Raman and ssNMR technique. SrLiAl3N4:Eu2+ presents a narrow band red phosphor for reducing near infrared region emission. In this study, SrLiAl3N4:Eu2+ red phosphor was prepared through a high-pressure solid-state reaction and was coated with organosilica layers to improve water resistance. The coated samples exhibited excellent moisture resistance while retaining external quantum efficiency in high temperature and high humidity. This study provides valuable information on the stimulation of nitride phosphors in LEDs

In this chapter, we review our recent work on blue laser diode-based visible light communication and solid-state lighting. Gallium nitride (GaN) phosphor-converted white light-emitting diodes (Pc-WLEDs) are emerging as an indispensable solid-state lighting (SSL) source for next-generation display system and the lighting industry. Together with the function of lighting, visible light communication (VLC) using Pc-WLEDs has gained increasing attention to fulfill the growing demand for wireless data communication. Practically, the low modulation response and low emitting intensity of light-emitting diodes (LED) are the drawbacks for the development of ultrahigh-speed VLC and high-quality SSL system. Blue GaN laser diode (LD) and remote phosphor-based white light can be used for both high-speed VLC and SSL simultaneously. We demonstrated a color-rendering index (CRI) of 93.8, a correlated color temperature (CCT) of 4435 K, and a data rate of 1.6 Gbps under NRZ-OOK modulation by an exciting blue laser diode on narrowband green−/red-emitting composite phosphor film. This work opens up exciting possibilities for future high-speed indoor VLC and high-quality SSL.

Oxygen has returned to some dead zones, but many problems remain. As this chapter explains, nutrient input from agriculture in some regions has decreased because farmers use buffer zones, cover crops, and precision agriculture. But voluntary efforts to minimize nutrient pollution aren’t enough. In Iowa, the Des Moines Water Works, led by a charismatic CEO, Bill Stowe, unsuccessfully sued to reduce nitrate leaching from local farms. The value of government action has been demonstrated in Denmark, whereas its absence has led to many environmental problems in China. The chapter argues that one solution is tied to human health and climate change: our diet. Eating less, especially eating less red meat, would be better for our health, and it would reduce nutrient pollution and abate climate change. Agriculture accounts for nearly a third of all greenhouse gas emissions. The chapter ends by suggesting that the successful bans against DDT and phosphorus detergents are among the reasons to be optimistic about solving the dead-zone problem.

The Baltic Sea is a semi-enclosed sea with remarkable cyclonic circulation. The most attention must be paid to the local-scale factors playing the significant role in the overall figures. Fresh water inflow takes the majority of the mass budget income thus enabling local streams. The bathymetry of the Lithuanian Baltic zone is lowering gradually towards the open sea and has no significant deeps or depths. As the little exception there is a deeper basin, which stretches from the Curonian Spit until it reaches the approaches of the Southern Gotland Deep. The long-term investigations of spatial seasonal distribution of inorganic nutrients (nitrite, nitrate and orthophosphate) resulted to some regularities depending on prevailing wind scale duration and force. The results obtained during the experiment showed the complicacy of field structure. Extremely heterogeneous patterns of nutrients are formed when northern or eastern winds or breezes are prevailing. After the other wind directions significant decrease of heterogeneity was observed. Assessment showed that Curonian Lagoon water entering the Baltic Sea is enriched with dissolved inorganic nitrogen 6 times more and dissolved inorganic phosphorus concentration is higher by 2 times in comparison to the open sea values in winter.

Fertilization is a method to enhance tree growth and timber production. Ammonium nitrate and wood ash are commonly used fertilizers, which can be applied at the same time to increase levels of both nitrogen and other macro- and micronutrients. We studied how ammonium nitrate and wood ash fertilization affects photosynthetic activity and transpiration at leaf level in a deciduous tree plantation in former agricultural land with mineral soil, located in the central part of Latvia (Keipene parish). Additionally, we performed foliar and soil nutrient analyses. Our results support the notion that nitrogen fertilization may not result in increased photosynthetic activity. It is possible that the photosynthetic activity has increased at canopy scale along with increasing leaf area, not at leaf scale. Wood ash addition seems to have resulted in higher photosynthetic activity for hybrid alder, although it could not be explained with phosphorus availability. Although closely related to photosynthesis, in most cases transpiration was not positively affected by fertilization. Environmental factors, such as humidity, temperature and wind speed may have a greater effect on this process.

Enhanced forest growth may respond to demand of woody resources and contribute to the climate change mitigation. Forest soil treatment with fertilizers, as well as drainage and thinning enhance forest growth. The analysis of needles is an established method in forest science to identify the nutrient status in the forest stand and need for forest soil enrichment with fertilizers. The aim of this research is to estimate the efficiency of forest soil enrichment with wood ash and ammonium nitrate in order to eliminate nutrient deficiency in forest stands. Forest soil was enriched with wood ash fertilizer or ammonium nitrate in 2016–2017. The current year needles were collected from fertilized and control plots, from three trees in each plot. The samples were collected in the period 2018–2019. Total nitrogen (g kg-1), calcium (g kg-1), magnesium (g kg-1), and potassium (g kg-1) were analyzed in the collected samples. The chemical properties of collected needles were compared at the individual object level to estimate the impact of fertilizer on forest stand. A statistically significant increase in the concentrations of potassium and phosphorus was detected in some plots treated with wood ash and ammonium nitrate. In addition, a correlation analysis conducted between the variables of chemical properties of needles and soil showed few significant correlations between nutrient content in needles and in soil samples.

The research site consists of a pilot-scale surface flow constructed wetland at the farm Mezaciruli located in Zalenieki County, Jelgava Region, in the middle part of Latvia. The constructed wetland was installed in June 2014 to improve water quality in agricultural catchment and examine nutrient retention at the constructed wetland receiving surface and drainage runoff. The constructed wetland’s surface area of 0.37 ha corresponds to 0.5 % of the total catchment area. During the observation period of 32 months (2014-2017) water quality parameters such as total suspended solids (TSS), nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), total nitrogen (TN), orthophosphate-phosphorus (PO4-P), and total phosphorus (TP) were monitored twice a month using a grab sample approach. Retention efficiency for monitored water quality parameters was calculated based on their concentrations at the inlet and outlet. The monitoring results obtained during this study showed a reduction within the constructed wetland for all examined parameters. The concentrations of NO3-N, NH4-N and TN were reduced on average by 13 %, 15 % and 16 %, respectively. PO4-P and TP concentrations were reduced on average by 38 % and 36 %, respectively. Total suspended solids were reduced by 31% at the outlet of the constructed wetland. However, in some cases, an increase in nutrient concentrations in water leaving the constructed wetland was observed. Therefore, there is a need for further research to investigate causes of such increase.