published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

No description available.

The greenhouse industry is interested in light emitting diodes (LEDs) as a light source supplement to solar light to improve plant growth and development. Before LEDs can be adopted as supplemental light for greenhouse crops, plant responses to LED spectral quality need to be investigated. Tomato and cucumber seedlings were grown under different supplemental blue and red photon flux ratios (B:R ratios) under high (16-19 mol m⁻² d⁻¹) and low (5-9 mol m⁻² d⁻¹) solar daily light integrals (DLIs). The supplemental daily light integral was 3.6 mol m⁻² d⁻¹. A treatment without supplemental light served as a control. Both tomato and cucumber seedlings had increased growth rate and improved morphology when grown under the supplemental LED light compared to the control. However, no significant differences were observed for any growth and morphological parameters measured in this study between the different B:R ratios for both cucumber and tomato transplants under high DLI conditions. Cucumber seedlings showed a tendency to decrease dry mass, leaf number and leaf area under low DLI conditions with increasing B:R ratio. Tomato seedlings did not show any differences between the different B:R ratios under low DLI conditions. Seedlings growth and morphology under supplemental LED light were compared to those under supplemental high pressure sodium (HPS) light. Cucumber seedlings under supplemental HPS light had greater shoot dry mass than those under the supplemental red LED light. Tomato shoot dry mass showed no differences between the HPS and red LED supplemental light treatments. Cucumber seedlings were also grown under supplemental LED pulsed lighting and supplemental LED continuous lighting. Cucumber seedlings showed no differences in shoot dry mass and net photosynthetic rate between the treatments. Collectively, these studies concluded that red LED is preferred for supplemental lighting and the increase of blue light does not offer any benefits unless the efficiency of blue LEDs largely exceeds the red LEDs. The results of this research can be used for fixture development by LED manufactures and as a decision making tool for the adoption of supplemental LED lighting by greenhouse growers.

Increasing the rate of orthodontic tooth movement (OTM) can reduce risks such as periodontal disease and caries. This study investigated whether light emitting diode (LED) phototherapy could accelerate the rate of OTM. Orthodontic patients with bilaterally symmetric extraction of premolars were recruited. During space closure, LED phototherapy was applied to one side of the dental arch for a specified time and the contralateral side acted as the control. Space closure was measured immediately prior to, during and later in space closure. All 11 patients were compliant with LED application. The results revealed no significant changes in the rate of OTM with LED phototherapy over 3 months of extraction space closure. The findings were contrary to previous findings with laser phototherapy and could be related to the dosage or method of LED phototherapy delivery. Further investigations are needed to determine whether LED phototherapy application can influence the rate of OTM.

Tyrimų tikslas. Ištirti kietakūnio apšvietimo, pagrįsto šviesą emituojančių diodų technologija, panaudojimo galimybes žalumyninių daržovių, želmenų ir daigintų sėklų vidinės kokybės rodikliams valdyti. Mokslinis naujumas. Pirmą kartą nustatyta, kad raudona 638 nm šviesa ir jos derinys su raudona 669 nm, mėlyna 447 nm ir tolimąja raudona 731 nm šviesa paskatina nitratų redukcijos procesus salotose ir kitose žalumyninėse daržovėse. Nustatyta, kad reikšmingam teigiamam efektui žalumyninių daržovių vidinei kokybei pasiekti pakanka jas švitinti didelio tankio fotosintetiškai aktyvios raudonos 638 nm spinduliuotės srautu ~72 h prieš planuojamą derliaus nuėmimą. Pirmą kartą įvertintas kietakūnio apšvietimo spektro efektas skirtingų lietuviškų javų želmenų, lapinių ridikėlių ir daigintų sėklų antioksidacinėms savybėms. Nustatytas teigiamas raudonų 638, 669 nm, mėlynos 447 nm ir tolimosios raudonos 731 nm bangų ilgių deriniui papildomų žalios 518 nm ir geltonos 595 nm šviesos efektas natūraliai aukštomis bioaktyvių medžiagų koncentracijomis audiniuose išsiskiriančių žalumyninių daržovių ir želmenų antioksidacinėms savybėms. Darbo praktinė svarba. Įvertintos originalios konstrukcijos kietakūnio apšvietimo įrenginių taikymo žalumyninių daržovių vidinei kokybei gerinti galimybės. Remiantis darbe nustatytais dėsningumais, parengtas ir patentuotas žalingų nitratų kiekio augaluose sumažinimo, apšvitinant kietakūnio šviestuvo sukuriamu šviesos srautu, metodas ir įrenginys. Atliktų tyrimų... [toliau žr. visą tekstą] / The aim of the research was to investigate the usability of the solid state lighting, based on light emitting diode technology, for the management of nutritional quality indices in green vegetables and sprouts. Scientific originality. It was determined for the first time, that red 638 nm light and its combination with blue 447 nm, red 669 nm and far red 731 nm light promoted nitrate reduction processes in lettuce and other green vegetables. It is enough to irradiate green vegetables with the high flux of photosyntheticaly active 638 nm red light for ~72 h before harvesting for the pronounced positive effect on their internal quality. The effect of the solid-state lighting spectra on antioxidant properties of Lithuanian cereal greens, leafy radish and sprouted seeds was evaluated for the first time. The positive effect of green 518 nm and yellow 595 nm light, supplemental for the red 638, 669 nm light, blue 447 nm and far red 731 nm light on the antioxidant properties of green vegetables and sprouts, naturally containing higher concentrations of bioactive compounds, was determined. Practical value of the work. Solid-state lighting application possibilities for the improvement of green vegetable internal quality were evaluated. According to defined trends, the method and apparatus for the reduction of harmful nitrates in plants, when irradiating plants with the light flux generated by semiconductor lighting unit, was designed and patented. The complex investigations and... [to full text]

Tyrimų tikslas. Ištirti kietakūnio apšvietimo, pagrįsto šviesą emituojančių diodų technologija, panaudojimo galimybes žalumyninių daržovių, želmenų ir daigintų sėklų vidinės kokybės rodikliams valdyti. Mokslinis naujumas. Pirmą kartą nustatyta, kad raudona 638 nm šviesa ir jos derinys su raudona 669 nm, mėlyna 447 nm ir tolimąja raudona 731 nm šviesa paskatina nitratų redukcijos procesus salotose ir kitose žalumyninėse daržovėse. Nustatyta, kad reikšmingam teigiamam efektui žalumyninių daržovių vidinei kokybei pasiekti pakanka jas švitinti didelio tankio fotosintetiškai aktyvios raudonos 638 nm spinduliuotės srautu ~72 h prieš planuojamą derliaus nuėmimą. Pirmą kartą įvertintas kietakūnio apšvietimo spektro efektas skirtingų lietuviškų javų želmenų, lapinių ridikėlių ir daigintų sėklų antioksidacinėms savybėms. Nustatytas teigiamas raudonų 638, 669 nm, mėlynos 447 nm ir tolimosios raudonos 731 nm bangų ilgių deriniui papildomų žalios 518 nm ir geltonos 595 nm šviesos efektas natūraliai aukštomis bioaktyvių medžiagų koncentracijomis audiniuose išsiskiriančių žalumyninių daržovių ir želmenų antioksidacinėms savybėms. Darbo praktinė svarba. Įvertintos originalios konstrukcijos kietakūnio apšvietimo įrenginių taikymo žalumyninių daržovių vidinei kokybei gerinti galimybės. Remiantis darbe nustatytais dėsningumais, parengtas ir patentuotas žalingų nitratų kiekio augaluose sumažinimo, apšvitinant kietakūnio šviestuvo sukuriamu šviesos srautu, metodas ir įrenginys. Atliktų tyrimų... [toliau žr. visą tekstą] / The aim of the research was to investigate the usability of the solid state lighting, based on light emitting diode technology, for the management of nutritional quality indices in green vegetables and sprouts. Scientific originality. It was determined for the first time, that red 638 nm light and its combination with blue 447 nm, red 669 nm and far red 731 nm light promoted nitrate reduction processes in lettuce and other green vegetables. It is enough to irradiate green vegetables with the high flux of photosyntheticaly active 638 nm red light for ~72 h before harvesting for the pronounced positive effect on their internal quality. The effect of the solid-state lighting spectra on antioxidant properties of Lithuanian cereal greens, leafy radish and sprouted seeds was evaluated for the first time. The positive effect of green 518 nm and yellow 595 nm light, supplemental for the red 638, 669 nm light, blue 447 nm and far red 731 nm light on the antioxidant properties of green vegetables and sprouts, naturally containing higher concentrations of bioactive compounds, was determined. Practical value of the work. Solid-state lighting application possibilities for the improvement of green vegetable internal quality were evaluated. According to defined trends, the method and apparatus for the reduction of harmful nitrates in plants, when irradiating plants with the light flux generated by semiconductor lighting unit, was designed and patented. The complex investigations and... [to full text]

Increasing the rate of orthodontic tooth movement (OTM) can reduce risks such as periodontal disease and caries. This study investigated whether light emitting diode (LED) phototherapy could accelerate the rate of OTM. Orthodontic patients with bilaterally symmetric extraction of premolars were recruited. During space closure, LED phototherapy was applied to one side of the dental arch for a specified time and the contralateral side acted as the control. Space closure was measured immediately prior to, during and later in space closure. All 11 patients were compliant with LED application. The results revealed no significant changes in the rate of OTM with LED phototherapy over 3 months of extraction space closure. The findings were contrary to previous findings with laser phototherapy and could be related to the dosage or method of LED phototherapy delivery. Further investigations are needed to determine whether LED phototherapy application can influence the rate of OTM.

ZnO material based hetero-junctions are a potential candidate for the design andrealization of intrinsic white light emitting devices (WLEDs) due to several advantages overthe nitride based material system. During the last few years the lack of a reliable andreproducible p-type doping in ZnO material with sufficiently high conductivity and carrierconcentration has initiated an alternative approach to grow n-ZnO nanorods (NRs) on other ptypeinorganic and organic substrates. This thesis deals with ZnO NRs-hetero-junctions basedintrinsic WLEDs grown on p-SiC, n-SiC and p-type polymers. The NRs were grown by thelow temperature aqueous chemical growth (ACG) and the high temperature vapor liquid solid(VLS) method. The structural, electrical and optical properties of these WLEDs wereinvestigated and analyzed by means of scanning electron microscope (SEM), current voltage(I-V), photoluminescence (PL), cathodoluminescence (CL), electroluminescence (EL) anddeep level transient spectroscopy (DLTS). Room temperature (RT) PL spectra of ZnOtypically exhibit one sharp UV peak and possibly one or two broad deep level emissions(DLE) due to deep level defects in the bandgap. For obtaining detailed information about thephysical origin, growth dependence of optically active defects and their spatial distribution,especially to study the re-absorption of the UV in hetero-junction WLEDs structure depthresolved CL spectroscopy, is performed. At room temperature the CL intensity of the DLEband is increased with the increase of the electron beam penetration depth due to the increaseof the defect concentration at the ZnO NRs/substrate interface. The intensity ratio of the DLEto the UV emission, which is very useful in exploring the origin of the deep level emissionand the distribution of the recombination centers, is monitored. It was found that the deepcenters are distributed exponentially along the ZnO NRs and that there are more deep defectsat the root of ZnO NRs compared to the upper part. The RT-EL spectra of WLEDs illustrateemission band covering the whole visible range from 420 nm and up to 800 nm. The whitelightcomponents are distinguished using a Gaussian function and the components were foundto be violet, blue, green, orange and red emission lines. The origin of these emission lines wasfurther identified. Color coordinates measurement of the WLEDs reveals that the emitted lighthas a white impression. The color rendering index (CRI) and the correlated color temperature(CCT) of the fabricated WLEDs were calculated to be 80-92 and 3300-4200 K, respectively.

One dimensional (1-D), zinc oxide (ZnO) and copper (II) oxide (CuO), nanostructures have great potential for applications in the fields of optoelectronic and sensor devices. Research on nanostructures is a fascinating field that has evolved during the last few years especially after the utilization of the hydrothermal growth method. Using this method variety of nanostructures can be grown from solutions, it is a cheap, easy, and environment friendly approach. These nanostructures can be synthesized on various conventional and nonconventional substrates such as silicon, plastic, fabrics and paper etc. The primary purpose of the work presented in this thesis is to realize controllable growth of ZnO, CuO and nanohybrid ZnO/CuO nanostructures and to process and develop white light emitting diodes and sensor devices from the corresponding nanostructures. The first part of the thesis deals with ZnO nanostructures grown under different hydrothermal conditions in order to gain a better understanding of the growth. Possible parameters affecting the growth such as the pH, the growth temperature, the growth time, and the precursors  concentration which can alter the morphology of the nanostructures were investigated (paper 1). Utilizing the advantage of the low temperature for growth we synthesized ZnO nanostructures on different substrates, specifically on flexible substrates, which are likely to be integrated with flexible organic substrates for future foldable and disposable electronics (paper 2, 3). In the second part of the thesis, using the results and findings from the growth of ZnO nanostructures, it was possible to successfully implement ZnO nanostructures for white light emitting diodes (LEDs) on different flexible substrates (paper 4, 5). In paper 4 we realized a ZnO/polymer LED grown on a paper substrate. In paper 5 we extended the idea to print the ZnO nanorods/polymer hybrid LEDs with potential application to large area flexible displays. In the last part of the thesis, CuO and nanohybrid ZnO/CuO nanostructures were utilized to fabricate Ag+ detection and humidity sensors. In paper 6 we reported Ag+ selective electrochemical sensor based on the use of functionalized CuO nanopetals. To combine the advantages of both oxides nanostructures and to improve the performance we fabricated a pn-heterojuction using intrinsic n-ZnO nanorods and p-CuO nanostructures which were then utilized as an efficient humidity sensor (paper 7).