Colloidal quantum dots(QDs)are excellent optical gain materials that combine high material gain,a strong absorption of pump light,stability under strong light exposure and a suitability for solution-based processing.T...Colloidal quantum dots(QDs)are excellent optical gain materials that combine high material gain,a strong absorption of pump light,stability under strong light exposure and a suitability for solution-based processing.The integration of QDs in laser cavities that fully exploit the potential of these emerging optical materials remains,however,a challenge.In this work,we report on a vertical cavity surface emitting laser,which consists of a thin film of QDs embedded between two layers of polymerized chiral liquid crystal.Forward directed,circularly polarized defect mode lasing under nanosecond-pulsed excitation is demonstrated within the photonic band gap of the chiral liquid crystal.Stable and long-term narrow-linewidth lasing of an exfoliated free-standing,flexible film under water is obtained at room temperature.Moreover,we show that the lasing wavelength of this flexible cavity shifts under influence of pressure,strain or temperature.As such,the combination of solution processable and stable inorganic QDs with high chiral liquid crystal reflectivity and effective polymer encapsulation leads to a flexible device with long operational lifetime,that can be immersed in different protic solvents to act as a sensor.展开更多
There is a rapidly growing demand to use silicon and silicon nitride（Si3N4） integrated photonics for sensing applications, ranging from refractive index to spectroscopic sensing. By making use of advanced CMOS techn...There is a rapidly growing demand to use silicon and silicon nitride（Si3N4） integrated photonics for sensing applications, ranging from refractive index to spectroscopic sensing. By making use of advanced CMOS technology,complex miniaturized circuits can be easily realized on a large scale and at a low cost covering visible to mid-IR wavelengths. In this paper we present our recent work on the development of silicon and Si3N4-based photonic integrated circuits for various spectroscopic sensing applications. We report our findings on waveguide-based absorption, and Raman and surface enhanced Raman spectroscopy. Finally we report on-chip spectrometers and on-chip broadband light sources covering very near-IR to mid-IR wavelengths to realize fully integrated spectroscopic systems on a chip.展开更多
Quantum dots(QDs) offer an interesting alternative for traditional phosphors in on-chip light-emitting diode(LED) configurations.Earlier studies showed that the spectral efficiency of white LEDs with high color render...Quantum dots(QDs) offer an interesting alternative for traditional phosphors in on-chip light-emitting diode(LED) configurations.Earlier studies showed that the spectral efficiency of white LEDs with high color rendering index(CRI) values could be considerably improved by replacing red-emitting nitride phosphors with narrowband QDs.However,the red QDs in these studies were cadmium-based,which is a restricted element in the EU and certain other countries.The use of InP-based QDs,the most promising Cd-free alternative,is often presented as an inferior solution because of the broader linewidth of these QDs.However,while narrow emission lines are the key to display applications that require a large color gamut,the spectral efficiency penalty of this broader emission is limited for lighting applications.Here,we report efficient,high-CRI white LEDs with an on-chip color converter coating based on red InP/ZnSe QDs and traditional green/yellow powder phosphors.Using InP/ZnSe QDs with a quantum yield of nearly 80% and a full width at half-maximum of 45 nm,we demonstrate high spectral efficiency for white LEDs with very high CRI values.One of the best experimental results in terms of both luminous efficacy and color rendering performance is a white LED with an efficacy of 132 lm/W,and color rendering indices of R_(a)≈90,R9 ≈50 for CCT ≈4000 K.These experimental results are critically compared with theoretical benchmark values for white LEDs with on-chip downconversion from both phosphors and red Cd-based QDs.The various loss mechanisms in the investigated white LEDs are quantified with an accurate simulation model,and the main impediments to an even higher efficacy are identified as the blue LED wall-plug Quantum dots(QDs) offer an interesting alternative for traditional phosphors in on-chip light-emitting diode(LED) configurations.Earlier studies showed that the spectral efficiency of white LEDs with high color rendering index(CRI) values could be considerably improved by replacing red-emitting nitride phosphors with narrowband QDs.However,the red QDs in these studies were cadmium-based,which is a restricted element in the EU and certain other countries.The use of In P-based QDs,the most promising Cd-free alternative,is often presented as an inferior solution because of the broader linewidth of these QDs.However,while narrow emission lines are the key to display applications that require a large color gamut,the spectral efficiency penalty of this broader emission is limited for lighting applications.Here,we report efficient,high-CRI white LEDs with an on-chip color converter coating based on red In P/Zn Se QDs and traditional green/yellow powder phosphors.Using In P/Zn Se QDs with a quantum yield of nearly 80% and a full width at half-maximum of 45 nm,we demonstrate high spectral efficiency for white LEDs with very high CRI values.One of the best experimental results in terms of both luminous efficacy and color rendering performance is a white LED with an efficacy of 132 lm/W,and color rendering indices of Ra≈ 90,R9 ≈ 50 for CCT ≈ 4000 K.These experimental results are critically compared with theoretical benchmark values for white LEDs with on-chip downconversion from both phosphors and red Cd-based QDs.The various loss mechanisms in the investigated white LEDs are quantified with an accurate simulation model,and the main impediments to an even higher efficacy are identified as the blue LED wall-plug efficiency and light recycling in the LED package.展开更多
2D materials are considered for applications that require strong light-matter interaction because of the apparently giant oscillator strength of the exciton transitions in the absorbance spectrum.Nevertheless,the effe...2D materials are considered for applications that require strong light-matter interaction because of the apparently giant oscillator strength of the exciton transitions in the absorbance spectrum.Nevertheless,the effective oscillator strengths of these transitions have bee n scarcely reported,nor is there a con sistent interpretati on of the obtained values.Here,we analyse the transition dipole moment and the ensuing oscillator strength of the exciton transition in 2D CdSe nanoplatelets by means of the optically induced Stark effect(OSE).Intriguingly,we find that the exciton absorption line reacts to a high intensity optical field as a transition with an oscillator strength FStark that is 50 times smaller than expected based on the linear absorption coefficient.We propose that the pronounced exciton absorption line should be seen as the sum of multiple,low oscillator strength transitions,rather than a single high oscillator strength one,a feat we assign to strong exciton center-of-mass localization.Within the quantum mechanical description of excitons,this 50-fold difference between both oscillator strengths corresponds to the ratio between the cohere nee area of the exciton's center of mass and the total area,which yields a coherence area of a mere 6.1 nm2.Since we find that the coherence area in creases with reducing temperature,we conclude that thermal effects,related to lattice vibrations,contribute to exciton localization.In further support of this localization model,we show that FStark is in dependent of the n anoplatelet area,correctly predicts the radiative lifetime,and lines up for strongly confined quantum dot systems.展开更多
文摘Colloidal quantum dots(QDs)are excellent optical gain materials that combine high material gain,a strong absorption of pump light,stability under strong light exposure and a suitability for solution-based processing.The integration of QDs in laser cavities that fully exploit the potential of these emerging optical materials remains,however,a challenge.In this work,we report on a vertical cavity surface emitting laser,which consists of a thin film of QDs embedded between two layers of polymerized chiral liquid crystal.Forward directed,circularly polarized defect mode lasing under nanosecond-pulsed excitation is demonstrated within the photonic band gap of the chiral liquid crystal.Stable and long-term narrow-linewidth lasing of an exfoliated free-standing,flexible film under water is obtained at room temperature.Moreover,we show that the lasing wavelength of this flexible cavity shifts under influence of pressure,strain or temperature.As such,the combination of solution processable and stable inorganic QDs with high chiral liquid crystal reflectivity and effective polymer encapsulation leads to a flexible device with long operational lifetime,that can be immersed in different protic solvents to act as a sensor.
基金ERC-In Spectra Advanced Grant, ERC-MIRACLE, ERC-ULPPIC and Methusalem (Smart Photonics Chips) for their supportfunding agencies IWT and FWO that helped in carrying out various parts of the work presented in the paper
文摘There is a rapidly growing demand to use silicon and silicon nitride（Si3N4） integrated photonics for sensing applications, ranging from refractive index to spectroscopic sensing. By making use of advanced CMOS technology,complex miniaturized circuits can be easily realized on a large scale and at a low cost covering visible to mid-IR wavelengths. In this paper we present our recent work on the development of silicon and Si3N4-based photonic integrated circuits for various spectroscopic sensing applications. We report our findings on waveguide-based absorption, and Raman and surface enhanced Raman spectroscopy. Finally we report on-chip spectrometers and on-chip broadband light sources covering very near-IR to mid-IR wavelengths to realize fully integrated spectroscopic systems on a chip.
文摘Quantum dots(QDs) offer an interesting alternative for traditional phosphors in on-chip light-emitting diode(LED) configurations.Earlier studies showed that the spectral efficiency of white LEDs with high color rendering index(CRI) values could be considerably improved by replacing red-emitting nitride phosphors with narrowband QDs.However,the red QDs in these studies were cadmium-based,which is a restricted element in the EU and certain other countries.The use of InP-based QDs,the most promising Cd-free alternative,is often presented as an inferior solution because of the broader linewidth of these QDs.However,while narrow emission lines are the key to display applications that require a large color gamut,the spectral efficiency penalty of this broader emission is limited for lighting applications.Here,we report efficient,high-CRI white LEDs with an on-chip color converter coating based on red InP/ZnSe QDs and traditional green/yellow powder phosphors.Using InP/ZnSe QDs with a quantum yield of nearly 80% and a full width at half-maximum of 45 nm,we demonstrate high spectral efficiency for white LEDs with very high CRI values.One of the best experimental results in terms of both luminous efficacy and color rendering performance is a white LED with an efficacy of 132 lm/W,and color rendering indices of R_(a)≈90,R9 ≈50 for CCT ≈4000 K.These experimental results are critically compared with theoretical benchmark values for white LEDs with on-chip downconversion from both phosphors and red Cd-based QDs.The various loss mechanisms in the investigated white LEDs are quantified with an accurate simulation model,and the main impediments to an even higher efficacy are identified as the blue LED wall-plug Quantum dots(QDs) offer an interesting alternative for traditional phosphors in on-chip light-emitting diode(LED) configurations.Earlier studies showed that the spectral efficiency of white LEDs with high color rendering index(CRI) values could be considerably improved by replacing red-emitting nitride phosphors with narrowband QDs.However,the red QDs in these studies were cadmium-based,which is a restricted element in the EU and certain other countries.The use of In P-based QDs,the most promising Cd-free alternative,is often presented as an inferior solution because of the broader linewidth of these QDs.However,while narrow emission lines are the key to display applications that require a large color gamut,the spectral efficiency penalty of this broader emission is limited for lighting applications.Here,we report efficient,high-CRI white LEDs with an on-chip color converter coating based on red In P/Zn Se QDs and traditional green/yellow powder phosphors.Using In P/Zn Se QDs with a quantum yield of nearly 80% and a full width at half-maximum of 45 nm,we demonstrate high spectral efficiency for white LEDs with very high CRI values.One of the best experimental results in terms of both luminous efficacy and color rendering performance is a white LED with an efficacy of 132 lm/W,and color rendering indices of Ra≈ 90,R9 ≈ 50 for CCT ≈ 4000 K.These experimental results are critically compared with theoretical benchmark values for white LEDs with on-chip downconversion from both phosphors and red Cd-based QDs.The various loss mechanisms in the investigated white LEDs are quantified with an accurate simulation model,and the main impediments to an even higher efficacy are identified as the blue LED wall-plug efficiency and light recycling in the LED package.
基金from FWO-Vlaanderen(12K8216N)Z.H.ack no wledges the Research Foundation Flanders(research projects 17006602 and G0F0920N)+1 种基金Ghent University(GOA no.01G01513)for funding.AJ.H acknowledges the ERC and NWO-TTW.S.Bisschop is acknowledged for SEM imaging of the platelet layers and K.De Nolf for help with the CdSe QD/platelet synthesis respectively.This project has received fun ding from the European Research Council(ERC)under the European Union's Horizon 2020 research and innovation program(grant agreement no.714876 PHOCONA).
文摘2D materials are considered for applications that require strong light-matter interaction because of the apparently giant oscillator strength of the exciton transitions in the absorbance spectrum.Nevertheless,the effective oscillator strengths of these transitions have bee n scarcely reported,nor is there a con sistent interpretati on of the obtained values.Here,we analyse the transition dipole moment and the ensuing oscillator strength of the exciton transition in 2D CdSe nanoplatelets by means of the optically induced Stark effect(OSE).Intriguingly,we find that the exciton absorption line reacts to a high intensity optical field as a transition with an oscillator strength FStark that is 50 times smaller than expected based on the linear absorption coefficient.We propose that the pronounced exciton absorption line should be seen as the sum of multiple,low oscillator strength transitions,rather than a single high oscillator strength one,a feat we assign to strong exciton center-of-mass localization.Within the quantum mechanical description of excitons,this 50-fold difference between both oscillator strengths corresponds to the ratio between the cohere nee area of the exciton's center of mass and the total area,which yields a coherence area of a mere 6.1 nm2.Since we find that the coherence area in creases with reducing temperature,we conclude that thermal effects,related to lattice vibrations,contribute to exciton localization.In further support of this localization model,we show that FStark is in dependent of the n anoplatelet area,correctly predicts the radiative lifetime,and lines up for strongly confined quantum dot systems.
