Angularly uniform white light-emitting diodes using an integrated reflector cup

We report on white light-emitting diodes (LEDs) with a truncated-conical (TC) geometry produced by laser micromachining. A blue LED was shaped into a circular disc with 50°-inclined sidewall using a modified laser micromachining setup. A layer of Al was coated onto the inclined sidewall and the bottom surface to form an integrated reflector. Due to the highly reflective mirror, laterally propagating photons are redirected into the upward direction, contributing to an increase of 21.7% of light intensity in the normal direction. With quantum dots applied to the surface, white light emission from this TC-LED structure demonstrated a 37% enhancement in color uniformity, compared with a conventional device. © 2010 IEEE.published_or_final_versio

Incidence and Growth of Patent Thickets - The Impact of Technological Opportunities and Complexity

We investigate incidence and evolution of patent thickets. Our empirical analysis is based on a theoretical model of patenting in complex and discrete technologies. The model cap- tures how competition for patent portfolios and complementarity of patents affect patent- ing incentives. We show that lower technological opportunities increase patenting in- centives in complex technologies while they decrease incentives in discrete technologies. Also, more competitors increase patenting incentives in complex technologies and reduce them in discrete technologies. To test these predictions a new measure of the density of patent thickets is introduced. European patent citations are used to construct measures of fragmentation and technological opportunity. Our empirical analysis is based on a panel capturing patenting behavior of 2074 firms in 30 technology areas over 15 years. GMM estimation results confirm the predictions of our theoretical model. The results show that patent thickets exist in 9 out of 30 technology areas. We find that decreased technological opportunities are a surprisingly strong driver of patent thicket growth

The Control Method for Wavelength-Based CCT of Natural Light Using Warm/Cool White LED

Reproducing circadian patterns of natural light through lighting requires technology that can control correlated color temperature (CCT) and short wavelength ratio (SWR) simultaneously. This study proposes a method for controlling wavelength-based CCT of natural light using LED light sources. First, the spectral power distribution (SPD) of each channel of the test lighting (two-channel LED lighting with warm white and cool white) is identified through actual measurement. Next, CCT and SWR are calculated based on the additive mixing of SPD using the mixing ratio from the measured SPD. Finally, the regression equations for mixing ratio-CCT and mixing ratio-SWR are derived through regression analysis. These equations are then utilized to implement a wavelength-based CCT control algorithm. For performance and evaluation purposes, natural light reproduction experiments were conducted, achieving a mean error of 94.5K for CCT and 1.5% for SWR

Incidence and Growth of Patent Thickets - The Impact of Technological Opportunities and Complexity

We investigate incidence and evolution of patent thickets. Our empirical analysis is based on a theoretical model of patenting in complex and discrete technologies. The model captures how competition for patent portfolios and complementarity of patents affect patenting incentives. We show that lower technological opportunities increase patenting incentives in complex technologies while they decrease incentives in discrete technologies. Also, more competitors increase patenting incentives in complex technologies and reduce them in discrete technologies. To test these predictions a new measure of the density of patent thickets is introduced. European patent citations are used to construct measures of fragmentation and technological opportunity. Our empirical analysis is based on a panel capturing patenting behavior of 2074 firms in 30 technology areas over 15 years. GMM estimation results confirm the predictions of our theoretical model. The results show that patent thickets exist in 9 out of 30 technology areas. We find that decreased technological opportunities are a surprisingly strong driver of patent thicket growth

The development of the toner density sensor for closed-loop feedback laser printer calibration

A new infrared (IR) sensor was developed for application in closed-loop feedback printer calibration as it relates to monochrome (black toner only) laser printers. The toner density IR sensor (TDS) was introduced in the early 1980’s; however, due to cost and limitation of technologies at the time, implementation was not accomplished until within the past decade. Existing IR sensor designs do not discuss/address: • EMI (electromagnetic interference) effects on the sensor due to EP (electrophotography) components • Design considerations for environmental conditions • Sensor response time as it affects printer process speed The toner density sensor (TDS) implemented in the Lexmark E series printer reduces these problems and eliminates the use of the current traditional “open-loop” (meaning feedback are parameters not directly affecting print darkness such as page count, toner level, etc.) calibration process where print darkness is adjusted using previously calculated and stored EP process parameters. The historical process does not have the ability to capture cartridge component variation and environmental changes which affect print darkness variation. The TDS captures real time data which is used to calculate EP process parameters for the adjustment of print darkness; as a result, greatly reducing variations uncontrolled by historical printer calibration. Specifically, the first and primary purpose of this research is to reduce print darkness variation using the TDS. The second goal is to mitigate the TDS EMI implementation issue for reliable data accuracy

An investigation into novel red emitting phosphors and their applications

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.New red emitting phosphors, based on the double tungstate/molybdates, were discovered. Some were able to retain their luminous efficacy after substituting Y3+ for Eu3+, reducing the cost of the phosphor. This substitution was attempted for existing commercial red emitting phosphors and proved unsuccessful. Another set of phosphors based on these lattices were discovered and the emitted luminous efficacy was 140% greater than other reported Eu3+ phosphors. The best of these was Na2WO4MoO4Eu0.44Al1.34Sm0.011. The integration of phosphors to the lighting application was also studied, including improvements in light extraction for existing phosphors. ACEL panels are currently applied to many applications and were briefly examined. The more recent OLED technology was investigated and comparisons can be drawn with the ACEL panels. LEDs were also a focus of the work with a new method developed for remote application of phosphors to LEDs, based on a dome shaped encapsulant, and this was adopted commercially by a high brightness LED manufacturer. The studies on the phosphors reported herein were aimed at integrating these into commercial applications. Although this was not achieved as brightness and particles size were problematic, if it is demonstrated that further development of the synthetic methods produce phosphors with suitable attributes, this may lead to the integration in applications.Department of Trade and Industry (DTI), Enfis, the Knowledge Transfer Partnership (KTP) and the Technology Strategy Board (TSB

Functional oxides for optoelectronics

Il riscaldamento globale è tra le problematiche più urgenti che dobbiamo affrontare. Diminuire il consumo energetico e incrementare l’energia prodotta da fonti rinnovabili piuttosto che dai combustibili fossili sono azioni fondamentali per affrontare il cambiamento climatico. Dato che l’illuminazione è responsabile del 20% del consumo totale di energia e che il fotovoltaico è tra le fonti di energia rinnovabile che è cresciuta di più negli ultimi decenni, l’optoelettronica riveste un ruolo centrale in questa sfida. Molti degli impressionanti miglioramenti raggiunti negli ultimi decenni in questo campo sono stati resi possibili dallo sviluppo e dall’ottimizzazione dei materiali impiegati. Film sottili e nanostrutture di ossidi sono stati studiati in questo lavoro come una possibile soluzione a problematiche nel settore dell’optoelettronica. In particolare, nanocristalli di CsPbBr3 sono di largo interesse come emettitori di luce, ma risultano poco stabili quando esposti a umidità, solventi polari, ecc. Di conseguenza, nanocristalli di CsPbBr3 sono stati incapsulati in un guscio di silica (CsPbBr3@SiO2) sfruttando una reazione tra l’anidride maleica e il legante oleilammina sulla superficie del CsPbBr3. In particolare, nanocristalli di Cs4PbBr6 vengono convertiti dall’anidride maleica in nanocristalli di CsPbBr3 e l’aggiunta di un precursore della silica permette l’incapsulamento. Ulteriori esperimenti hanno rivelato il ruolo cruciale dei nanocristalli di Cs4PbBr6 e dell’ambiente di reazione ottenuto dopo la loro conversione per garantire la formazione di CsPbBr3@SiO2. Questo lavoro apre la strada allo studio della reattività dei leganti superficiali per l’incapsulazione dei nanocristalli, ma anche per strade alternative per lo scambio o la rimozione dei liganti, una nuova chimica per nanomateriali più stabili. Gli ossidi funzionali sono stati investigati anche in forma di film sottili per applicazioni fotovoltaiche. In dettaglio, la commercializzazione di celle solari a base di materiali emergenti come Cu(In,Ga)Se2 e Sb2Se3 contengono un buffer layer a base di CdS, un composto altamente tossico che ostacola la loro commercializzazione. Zn(1-x)MgxO è stato identificato come un potenziale materiale alternativo per celle solari a base di Cu(In,Ga)Se2 mentre la titania per Sb2Se3. Film sottili di Zn(1-x)MgxO sono stati preparati mediante deposizione da bagno chimico su substrati di vetro. E’ stato studiato il ruolo dell’etanolammina e dell’acido citrico insieme al contenuto di Mg sulle proprietà del film con lo scopo di impiegare questi film come buffer layer in celle solari al Cu(In,Ga)Se2 anche mediate calcoli degli equilibri in soluzione per comprendere il meccanismo di formazione del film. Analogamente, film sottili di titania sono stati preparati mediante spin coating su ossido di stagno drogato fluoro. Un trattamento acido è stato investigato per controllare il drogaggio nel film sottile di titania al fine di ottimizzare le performance della cella solare. Alcuni calcoli termodinamici sono stati eseguiti per confrontare la stabilità di fasi a diverso contenuto di titanio e di ossigeno.Nowadays, global warming is among the most urgent challenges that we have to meet. Decrease the energy consumption and enhance the amount of energy produced trough renewable sources rather than fossil fuels are imperative actions to deal with climate change. Since lighting is responsible of about 20 % of the total energy consumption and since photovoltaics is among the renewable energy source that grew more in the last decades, optoelectronics is a central field in such a challenge. Many of the crucial improvements that have been reached in the last decades in this field were made possible thanks to the development and optimization of the materials involved. In this study, oxides were investigated at the nanoscale and in the form of thin films as valuable solutions to current issues in modern optoelectronics. In particular, CsPbBr3 nanocrystals are interesting materials for light emission applications, but they suffer from poor stability against moisture, polar solvents etc. As a consequence, the reaction between maleic anhydride and the oleylamine capping ligand was exploited to encapsulate CsPbBr3 nanocrystals in SiO2 shells (CsPbBr3@SiO2). Maleic anhydride converted the starting Cs4PbBr6 nanocrystals into CsPbBr3 ones, and the addition of silica precursor promoted the shell growth. Further experiments revealed the crucial role played by Cs4PbBr6 nanocrystals as a starting material and of the reaction environment in order to successfully grow CsPbBr3@SiO2. This study paves the way for the exploitation of the reactivity of surface capping ligands for the encapsulation of nanocrystals, and potentially also for ligand exchange or stripping, a new chemistry route for more stable nanomaterials. Functional oxides were also investigated in the form of thin films for solar cell applications. Cu(In,Ga)Se2 and Sb2Se3 are emerging photovoltaic technologies whose market availability is limited by the presence of a toxic CdS buffer layer. Zn(1-x)MgxO was identified as a potential alternative oxide for the deposition of buffer layers for Cu(In,Ga)Se2 solar cells, whereas titania was investigated for cells based on Sb2Se3. In view of their application as buffer layers in Cu(In,Ga)Se2 solar cells, Zn(1-x)MgxO thin films were grown trough chemical bath deposition onto soda lime glass, in order to optimize the extent of Mg incorporation and the morphology of the film, the role of the complexing agent citric acid together with the nominal Mg amount was investigated. Likewise, titania thin films were prepared trough spin coating onto fluorine-doped thin oxide substrates. Several attempts were devoted to control and measure the n-type doping of the titania layers trough an acidic treatment with the final goal of improving the solar cell performance. Lastly, thermodynamic calculations allowed a stability comparison among TixOy species