Organic light-emitting diodes(OLEDs)have important applications in the field of next-generation displays and lighting,and phosphorescent iridium complexes are an important class of electroluminescent phosphorescent ma...Organic light-emitting diodes(OLEDs)have important applications in the field of next-generation displays and lighting,and phosphorescent iridium complexes are an important class of electroluminescent phosphorescent materials.In this paper,Ir(bmppy)_(3),tris(4-methyl-2,5-diphenylpyridine)iridium,was synthesized and elvaluted for photo-physical characteristics.Single crystals suitale for X-ray diffraction(XRD)were grown from a mixture solvent of dichloromethane and absolute ethanol.The composition and structur of Ir(bmppy)_(3)were determined by element analysis,NMR spectra and XRD.The complex crystallizes in the monoclinic symmetry with the space group P21/c with a slightly distorted octahedral configuration.As measured by UV-Visible and photoluminescence spectra,Ir(bmppy)_(3) displays a maximum emission at at 527 nm at ambient temperature,a typical green-emitting profile.The complex has potential for application in the OLED industry.展开更多
Display devices have significantly changed our daily life for decades,from the watches,television,to the laptop and smartphone.As the desire of advanced display device with high-resolution,long operation life and ligh...Display devices have significantly changed our daily life for decades,from the watches,television,to the laptop and smartphone.As the desire of advanced display device with high-resolution,long operation life and lightweight properties,several display techniques have been demonstrated.There are mainly four types of electronic display device:cathode ray tube(CRT),liquid-crystal display(LCD),organic light-emitting diode(OLED),and micro-LED.Due to the different working principles and device structures,each type of display device has its special characteristic properties.The performance of devices could be adjusted through the material selection or device design.With careful device structure regulation,not only the efficiency but also the stability would be improved.Herein,a brief review of innovative strategies towards the structure design is presented.展开更多
A novel full color SOP（system on panel） AMOLED display based on the MIUC polycrystalline silicon TFT technique, and a new control circuit for the panel, which can deal with both VGA and DVI input signals have been d...A novel full color SOP（system on panel） AMOLED display based on the MIUC polycrystalline silicon TFT technique, and a new control circuit for the panel, which can deal with both VGA and DVI input signals have been developed. To realize gray-scale a sub-frame technique has been designed and im- plemented by FPGA device, in which an 120 module has been inserted. Through actual circuit, the whole design has been proven and the advantages of the SOP AMOLED display panel have been confirmed.展开更多
Beam shaping is required for semiconductor lasers to achieve high optical fiber coupling efficiency in many applications.But the positioning errors on optics may reduce beam shaping effects,and then lead to low optica...Beam shaping is required for semiconductor lasers to achieve high optical fiber coupling efficiency in many applications.But the positioning errors on optics may reduce beam shaping effects,and then lead to low optical fiber coupling efficiency.In this work,the positioning errors models for the single emitter laser diode beam shaping system are established.Moreover,the relationships between the errors and the beam shaping effect of each shapers are analysed.Subsequently,the relationship between the errors and the optical fiber coupling efficiency is analysed.The result shows that position errors in the Z axis direction on the fast axis collimator have the greatest influence on the shaping effect,followed by the position errors in the Z axis direction on the converging lens,which should be strictly suppressed in actual operation.Besides,the position errors have a significant influence on the optical fiber coupling efficiency and need to be avoided.展开更多
The practical application of semiconductor-based high-efficiency white-light sources, also known as light-emitting diodes, or LEDs, is a recent development of Japanese engineering. This development could be a game-cha...The practical application of semiconductor-based high-efficiency white-light sources, also known as light-emitting diodes, or LEDs, is a recent development of Japanese engineering. This development could be a game-changer for lighting worldwide, given that current power consumption for lighting accounts for 16% of the total electricity consumption in Japan.展开更多
This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency o...This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency of timer output waveform which is measured using a digital storage oscillator(DSO)is almost linearly proportional to the applied input voltage.Hence we obtain a linear relationship between the frequency of timer output waveform and the input voltage.Because of its quasi-digital output,the main advantages of this developed converter are linear input-output relationship,small size,easy portabilityand high cost performance.In addition,the timer output waveform can be directly interfaced with personal computer or microprocessor/microcontroller for further processing of the input voltage signal without intervening any analog-to-digital converter(ADC).展开更多
The experimental study on negative capacitance（NO） of various light-emitting diodes（LEDs） is presented. Experimental result shows that all LEDs display the NO phenomenon. The voltage modulated electroluminescence...The experimental study on negative capacitance（NO） of various light-emitting diodes（LEDs） is presented. Experimental result shows that all LEDs display the NO phenomenon. The voltage modulated electroluminescence（VMEL） experiment confirms that the reason of negative capacitance is the strong recombination of the injected carriers in the active region of luminescence. The measures also verify that the dependence of NO on voltage and frequency in different LEDs is similar. NO phenomenon is more obvious with higher voltage or lower frequency.展开更多
A new dimmer using a mental-oxide-semiconductor field-effect transistor (MOSFET) for alternating-current (AC) directly driven light-emitting-diode (LED) lamp was presented. The control method of proposed dimmer is pul...A new dimmer using a mental-oxide-semiconductor field-effect transistor (MOSFET) for alternating-current (AC) directly driven light-emitting-diode (LED) lamp was presented. The control method of proposed dimmer is pulse width control (PWM) method. Compared with the conventional phase-controlled dimmer, the proposed PWM dimmer can produce sine wave and did not cause harmonics problem. Furthermore, the proposed control method did not amplify the light flicker due to the independence of input voltage. Therefore, the PWM dimmer can be used as the dimmer of the AC LED lamp instead of the conventional phase-controlled dimmer. The experimental result shows that the proposed PWM dimmer has good performances.展开更多
Colloidal semiconductor nanocrystals have been proven to be promising candidates for applications in low‐cost and high‐performance photovoltaics,bioimaging,and photocatalysis due to their novel size‐and shape‐depe...Colloidal semiconductor nanocrystals have been proven to be promising candidates for applications in low‐cost and high‐performance photovoltaics,bioimaging,and photocatalysis due to their novel size‐and shape‐dependent properties.Among the colloidal systems,I‐III‐VI semiconductor nanocrystals(NCs)have drawn much attention in the past few decades.Compared to binary NCs,ternary I‐III‐VI NCs not only exhibit low toxicity,but also a high performance similar to that of binary NCs.In this review,we mainly focus on the synthesis,properties,and applications of I‐III‐VI NCs.We summarize the major synthesis methods,analyze their photophysical and electronic properties,and highlight some of the latest applications of I‐III‐VI NCs in solar cells,light‐emitting diodes,bioimaging,and photocatalysis.Finally,based on the information reviewed,we highlight the existing problems and challenges.展开更多
White organic light-emitting diodes were fabricated by using 4,48-bis （2,28-diphenylvinyl） -1,18-bi- phenyl （DPVBi） as a dopant with a structure of ITO/4,4＂-bisEN-（1-naphthyl-1-）-N-phenyl-amino]-bi- phenyl （NP...White organic light-emitting diodes were fabricated by using 4,48-bis （2,28-diphenylvinyl） -1,18-bi- phenyl （DPVBi） as a dopant with a structure of ITO/4,4＂-bisEN-（1-naphthyl-1-）-N-phenyl-amino]-bi- phenyl （NPB,50 nm）/NPB：DPVBi （molecular weight ratio 10 ; 1,30 nm）/tris-（8-hydroxyquinoline）a- luminum（AIq：, ,20 nm）/LiF（1 nm）/Al. A broad emissive band with four major peaks of 438,464,496 and 520 nm was obtained by electroluminescence spectra,of which 438 nm-,464 nm- and 520 nm-peak come from emission of NPB, DPVBi and AIq3, respectively,and 496 nm-one resulted from the emissive superposition of three materials above. The emission from DPVBi was attributed to the charge trapping from NPB. The emission region was transferred partly from AIq3 to DPVBi-doped NPB by introducing the dopant DPVBi,which leads to emission of DPVBi and an enhanced emission from NPB. The maxi- mum luminance and current efficiency were 4721 cd/m^2 at 22 V and 0.80 cd/A at 5V,respectively.展开更多
Through experiments and computer simulation,the influence of the energy levels of organic materials and electrode materials in the organic light-emitting diodes (OLEDs) on the device performances is discussed.Results ...Through experiments and computer simulation,the influence of the energy levels of organic materials and electrode materials in the organic light-emitting diodes (OLEDs) on the device performances is discussed.Results show that the device performances are influenced by not only the carrier injection barriers at the electrode interface but also the barriers at the organic heterojunction interface.This result is helpful to the selection of the organic materials and their arrangement in the optimal design of OLEDs.展开更多
Microcavity structure consisting of distributed Bragg reflector and metal aluminum mirror is designed. Using tris (8-hydroxyquinoline) aluminum as electron-transport layer and emissive layer, and N, N′-bis (3-methylp...Microcavity structure consisting of distributed Bragg reflector and metal aluminum mirror is designed. Using tris (8-hydroxyquinoline) aluminum as electron-transport layer and emissive layer, and N, N′-bis (3-methylphenyl)-N, N′-diphenylbenzidine as a hole-transport layer, microcavity organic light-emitting diodes(MOLEDs) are fabricated. Compared to the electroluminescence spectra of non-cavity OLEDs, the linewidth of the MOLEDs is compressed from 75 nm to 7 nm, and the peak intensity enhances by a factor of about 3. When the effective length of the microcavity is modified, resonance wavelength can be selectively scanned over a very wide range of wavelengths that cover almost 140 nm.展开更多
A power management unit （PMU） chip supplying dual panel supply voltage, which has a low electro-magnetic interference （EMI） characteristic and is favorable for miniaturization, is designed. A two-phase charge pump...A power management unit （PMU） chip supplying dual panel supply voltage, which has a low electro-magnetic interference （EMI） characteristic and is favorable for miniaturization, is designed. A two-phase charge pump circuit using external pumping capacitor increases its pumping current and works out the charge-loss problem by using bulk-potential biasing circuit. A low-power start-up circuit is also proposed to reduce the power consumption of the band-gap reference voltage generator. And the ring oscillator used in the ELVSS power circuit is designed with logic devices by supplying the logic power supply to reduce the layout area. The PMU chip is designed with MagnaChip＇s 0.25 μ high-voltage process. The driving currents of ELVDD and ELVSS are more than 50 mA when a SPICE simulation is done.展开更多
Much attention has been paid to white LEDs because of their potential applications in the illumination.The doping of rare earth ions plays an important role in the optical properties of yellow fluorescent powder.And m...Much attention has been paid to white LEDs because of their potential applications in the illumination.The doping of rare earth ions plays an important role in the optical properties of yellow fluorescent powder.And mainly aiming to raise the intensity and the luminous rate of the white LEDs and by photoluminescence and electroluminescence,the luminescence spectrum of yellow fluorescent powder bought from different places is measured.Furthermore, the luminous intensity in the normal direction and the angle distribution of half maximum power for the white LEDs packed with cylindrical Φ 5 epoxy on the same blue GaN chips are also measured under the same manufacture conditions. The results show that the yellow fluorescent powder bought from China mainland has higher optical output rate than that bought from China Taiwan and hence is more suitable to fabricate the white LEDs for practical use.展开更多
Photodiode＇s reflectance plays an important role regarding the relation between responsivity and the incident flux. In this work we analyze how the spectral reflectance changes among photodiodes from the same manufac...Photodiode＇s reflectance plays an important role regarding the relation between responsivity and the incident flux. In this work we analyze how the spectral reflectance changes among photodiodes from the same manufacturer and batch and how the reflectance of three standard photodiodes has drifted during six years. The results show that the reflectance changes from diode to diode within the same batch and also show that the reflectance ofphotodiodes changes on time. This ageing is spectraUy dependent.展开更多
White organic light-emitting diodes were fabricated by using a novel phosphorescence bis（1,2-diphenyl-1H-benzoimidazole）iridium（acetylacetonate）[（pbi）2Ir（acac）] as sensitizer and a fluorescent dye of 4- （dicy...White organic light-emitting diodes were fabricated by using a novel phosphorescence bis（1,2-diphenyl-1H-benzoimidazole）iridium（acetylacetonate）[（pbi）2Ir（acac）] as sensitizer and a fluorescent dye of 4- （dicyanomethylene）-2-t-butyl-6-（1,1,7,7-tetramethyljulolidyl-9-enyl）-4H-pyran （DCJTB） codoped into a carbazole polymer of poly（N-vinylcarbazole） （PVK）. Through characterizing the UV-Vis absorption spectra, the photoluminescence spectra of （pbi）2Ir（acac） and DCJTB, and the electroluminescence spectral properties of the WOLEDs, the energy transfer mechanisms of the codoped polymer system were deduced. The results demonstrate that the luminescent spectra with different intensity of （pbi）2Ir（acac） and DCJTB were co-existent in the EL spectra of the blended system, which is ascribed to an incomplete energy transfer process in the EL process. The efficient Forster and Dexter energy transfer between the host and the guests enabled a strong yellow emission from （pbi）2Ir（acac） and DCJTB, where （pbi）2Ir（acac） plays an important role as a phosphorescent sensitizer for DCJTB. With the blue emitting-layer of N,N＇-diphenyl-N,N＇-bis（1- naphthyl）（1,1＇-biphenyl）-4,4＇-diamine, the codoped system device achieved white emission. The codoped system showed that its Commissions Internationale de 1＇Eclairage coordinates were more independent of the variation of bias voltage than those of phosphorescent doped PVK systems.展开更多
The coupled DBR LED with one DBR for reflecting normal incidence light and the other for reflecting inclined incidence light has been grown by MOCVD. For improving the conventional DBR which was used to increase light...The coupled DBR LED with one DBR for reflecting normal incidence light and the other for reflecting inclined incidence light has been grown by MOCVD. For improving the conventional DBR which was used to increase light extraction efficiency in AIG-alnP red light LED is analyzed. At 20 mADc injection current, the LED peak wave length is 630 nm, and the light intensity of on axis is 137 mcd. The output light power is 2.32 mW. The light intensity and output light power have been improved compared with the conventional LEDs.展开更多
In terms of asymmetrical three-dimensional distribution(ID) of luminous intensity(LI) of light-emitting-diode(LED),a testing system was conducted in this study. Design and principle of the testing system were introduc...In terms of asymmetrical three-dimensional distribution(ID) of luminous intensity(LI) of light-emitting-diode(LED),a testing system was conducted in this study. Design and principle of the testing system were introduced. 31 photometers were placed on a concentric circle,and all of them were used to gather LI data of LED at the same time. The data acquisition card(DAC) was used to gather multichannel data and controlled motor. Experimental results indicated that the testing system had achieved the goal of testing three-dimensional distribution of LI. And each parameter could meet the requirements of industrial production and measurement.展开更多
文摘Organic light-emitting diodes(OLEDs)have important applications in the field of next-generation displays and lighting,and phosphorescent iridium complexes are an important class of electroluminescent phosphorescent materials.In this paper,Ir(bmppy)_(3),tris(4-methyl-2,5-diphenylpyridine)iridium,was synthesized and elvaluted for photo-physical characteristics.Single crystals suitale for X-ray diffraction(XRD)were grown from a mixture solvent of dichloromethane and absolute ethanol.The composition and structur of Ir(bmppy)_(3)were determined by element analysis,NMR spectra and XRD.The complex crystallizes in the monoclinic symmetry with the space group P21/c with a slightly distorted octahedral configuration.As measured by UV-Visible and photoluminescence spectra,Ir(bmppy)_(3) displays a maximum emission at at 527 nm at ambient temperature,a typical green-emitting profile.The complex has potential for application in the OLED industry.
基金Projects(71572028,71872027)supported by the National Natural Science Foundation of China。
文摘Display devices have significantly changed our daily life for decades,from the watches,television,to the laptop and smartphone.As the desire of advanced display device with high-resolution,long operation life and lightweight properties,several display techniques have been demonstrated.There are mainly four types of electronic display device:cathode ray tube(CRT),liquid-crystal display(LCD),organic light-emitting diode(OLED),and micro-LED.Due to the different working principles and device structures,each type of display device has its special characteristic properties.The performance of devices could be adjusted through the material selection or device design.With careful device structure regulation,not only the efficiency but also the stability would be improved.Herein,a brief review of innovative strategies towards the structure design is presented.
文摘A novel full color SOP（system on panel） AMOLED display based on the MIUC polycrystalline silicon TFT technique, and a new control circuit for the panel, which can deal with both VGA and DVI input signals have been developed. To realize gray-scale a sub-frame technique has been designed and im- plemented by FPGA device, in which an 120 module has been inserted. Through actual circuit, the whole design has been proven and the advantages of the SOP AMOLED display panel have been confirmed.
基金Project(51475479) supported by the National Natural Science Foundation of ChinaProject(2017YFB1104800) supported by the National Key Research and Development Program of China+2 种基金Project(2016GK2098) supported by the Key Research and Development Program of Hunan Province,ChinaProject(ZZYJKT2017-07) supported by the State Key Laboratory of High Performance Complex Manufacturing,Central South University,ChinaProject(JMTZ201804) supported by the Key Laboratory for Precision&Non-traditional Machining of Ministry of Education,Dalian University of Technology,China
文摘Beam shaping is required for semiconductor lasers to achieve high optical fiber coupling efficiency in many applications.But the positioning errors on optics may reduce beam shaping effects,and then lead to low optical fiber coupling efficiency.In this work,the positioning errors models for the single emitter laser diode beam shaping system are established.Moreover,the relationships between the errors and the beam shaping effect of each shapers are analysed.Subsequently,the relationship between the errors and the optical fiber coupling efficiency is analysed.The result shows that position errors in the Z axis direction on the fast axis collimator have the greatest influence on the shaping effect,followed by the position errors in the Z axis direction on the converging lens,which should be strictly suppressed in actual operation.Besides,the position errors have a significant influence on the optical fiber coupling efficiency and need to be avoided.
文摘The practical application of semiconductor-based high-efficiency white-light sources, also known as light-emitting diodes, or LEDs, is a recent development of Japanese engineering. This development could be a game-changer for lighting worldwide, given that current power consumption for lighting accounts for 16% of the total electricity consumption in Japan.
文摘This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency of timer output waveform which is measured using a digital storage oscillator(DSO)is almost linearly proportional to the applied input voltage.Hence we obtain a linear relationship between the frequency of timer output waveform and the input voltage.Because of its quasi-digital output,the main advantages of this developed converter are linear input-output relationship,small size,easy portabilityand high cost performance.In addition,the timer output waveform can be directly interfaced with personal computer or microprocessor/microcontroller for further processing of the input voltage signal without intervening any analog-to-digital converter(ADC).
基金This workis supported by the National Nature Science Founda-tion (Grant No.DMR-60376027)
文摘The experimental study on negative capacitance（NO） of various light-emitting diodes（LEDs） is presented. Experimental result shows that all LEDs display the NO phenomenon. The voltage modulated electroluminescence（VMEL） experiment confirms that the reason of negative capacitance is the strong recombination of the injected carriers in the active region of luminescence. The measures also verify that the dependence of NO on voltage and frequency in different LEDs is similar. NO phenomenon is more obvious with higher voltage or lower frequency.
文摘A new dimmer using a mental-oxide-semiconductor field-effect transistor (MOSFET) for alternating-current (AC) directly driven light-emitting-diode (LED) lamp was presented. The control method of proposed dimmer is pulse width control (PWM) method. Compared with the conventional phase-controlled dimmer, the proposed PWM dimmer can produce sine wave and did not cause harmonics problem. Furthermore, the proposed control method did not amplify the light flicker due to the independence of input voltage. Therefore, the PWM dimmer can be used as the dimmer of the AC LED lamp instead of the conventional phase-controlled dimmer. The experimental result shows that the proposed PWM dimmer has good performances.
文摘Colloidal semiconductor nanocrystals have been proven to be promising candidates for applications in low‐cost and high‐performance photovoltaics,bioimaging,and photocatalysis due to their novel size‐and shape‐dependent properties.Among the colloidal systems,I‐III‐VI semiconductor nanocrystals(NCs)have drawn much attention in the past few decades.Compared to binary NCs,ternary I‐III‐VI NCs not only exhibit low toxicity,but also a high performance similar to that of binary NCs.In this review,we mainly focus on the synthesis,properties,and applications of I‐III‐VI NCs.We summarize the major synthesis methods,analyze their photophysical and electronic properties,and highlight some of the latest applications of I‐III‐VI NCs in solar cells,light‐emitting diodes,bioimaging,and photocatalysis.Finally,based on the information reviewed,we highlight the existing problems and challenges.
文摘White organic light-emitting diodes were fabricated by using 4,48-bis （2,28-diphenylvinyl） -1,18-bi- phenyl （DPVBi） as a dopant with a structure of ITO/4,4＂-bisEN-（1-naphthyl-1-）-N-phenyl-amino]-bi- phenyl （NPB,50 nm）/NPB：DPVBi （molecular weight ratio 10 ; 1,30 nm）/tris-（8-hydroxyquinoline）a- luminum（AIq：, ,20 nm）/LiF（1 nm）/Al. A broad emissive band with four major peaks of 438,464,496 and 520 nm was obtained by electroluminescence spectra,of which 438 nm-,464 nm- and 520 nm-peak come from emission of NPB, DPVBi and AIq3, respectively,and 496 nm-one resulted from the emissive superposition of three materials above. The emission from DPVBi was attributed to the charge trapping from NPB. The emission region was transferred partly from AIq3 to DPVBi-doped NPB by introducing the dopant DPVBi,which leads to emission of DPVBi and an enhanced emission from NPB. The maxi- mum luminance and current efficiency were 4721 cd/m^2 at 22 V and 0.80 cd/A at 5V,respectively.
文摘Through experiments and computer simulation,the influence of the energy levels of organic materials and electrode materials in the organic light-emitting diodes (OLEDs) on the device performances is discussed.Results show that the device performances are influenced by not only the carrier injection barriers at the electrode interface but also the barriers at the organic heterojunction interface.This result is helpful to the selection of the organic materials and their arrangement in the optimal design of OLEDs.
文摘Microcavity structure consisting of distributed Bragg reflector and metal aluminum mirror is designed. Using tris (8-hydroxyquinoline) aluminum as electron-transport layer and emissive layer, and N, N′-bis (3-methylphenyl)-N, N′-diphenylbenzidine as a hole-transport layer, microcavity organic light-emitting diodes(MOLEDs) are fabricated. Compared to the electroluminescence spectra of non-cavity OLEDs, the linewidth of the MOLEDs is compressed from 75 nm to 7 nm, and the peak intensity enhances by a factor of about 3. When the effective length of the microcavity is modified, resonance wavelength can be selectively scanned over a very wide range of wavelengths that cover almost 140 nm.
文摘A power management unit （PMU） chip supplying dual panel supply voltage, which has a low electro-magnetic interference （EMI） characteristic and is favorable for miniaturization, is designed. A two-phase charge pump circuit using external pumping capacitor increases its pumping current and works out the charge-loss problem by using bulk-potential biasing circuit. A low-power start-up circuit is also proposed to reduce the power consumption of the band-gap reference voltage generator. And the ring oscillator used in the ELVSS power circuit is designed with logic devices by supplying the logic power supply to reduce the layout area. The PMU chip is designed with MagnaChip＇s 0.25 μ high-voltage process. The driving currents of ELVDD and ELVSS are more than 50 mA when a SPICE simulation is done.
文摘Much attention has been paid to white LEDs because of their potential applications in the illumination.The doping of rare earth ions plays an important role in the optical properties of yellow fluorescent powder.And mainly aiming to raise the intensity and the luminous rate of the white LEDs and by photoluminescence and electroluminescence,the luminescence spectrum of yellow fluorescent powder bought from different places is measured.Furthermore, the luminous intensity in the normal direction and the angle distribution of half maximum power for the white LEDs packed with cylindrical Φ 5 epoxy on the same blue GaN chips are also measured under the same manufacture conditions. The results show that the yellow fluorescent powder bought from China mainland has higher optical output rate than that bought from China Taiwan and hence is more suitable to fabricate the white LEDs for practical use.
文摘Photodiode＇s reflectance plays an important role regarding the relation between responsivity and the incident flux. In this work we analyze how the spectral reflectance changes among photodiodes from the same manufacturer and batch and how the reflectance of three standard photodiodes has drifted during six years. The results show that the reflectance changes from diode to diode within the same batch and also show that the reflectance ofphotodiodes changes on time. This ageing is spectraUy dependent.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.60425101）, the Program for the New Century Excellent Talents in University of Ministry of Education of China （No.NCET-06-0812）, and the Young Talent Project of University of Electronic Science and Technology of China （No.060206）.
文摘White organic light-emitting diodes were fabricated by using a novel phosphorescence bis（1,2-diphenyl-1H-benzoimidazole）iridium（acetylacetonate）[（pbi）2Ir（acac）] as sensitizer and a fluorescent dye of 4- （dicyanomethylene）-2-t-butyl-6-（1,1,7,7-tetramethyljulolidyl-9-enyl）-4H-pyran （DCJTB） codoped into a carbazole polymer of poly（N-vinylcarbazole） （PVK）. Through characterizing the UV-Vis absorption spectra, the photoluminescence spectra of （pbi）2Ir（acac） and DCJTB, and the electroluminescence spectral properties of the WOLEDs, the energy transfer mechanisms of the codoped polymer system were deduced. The results demonstrate that the luminescent spectra with different intensity of （pbi）2Ir（acac） and DCJTB were co-existent in the EL spectra of the blended system, which is ascribed to an incomplete energy transfer process in the EL process. The efficient Forster and Dexter energy transfer between the host and the guests enabled a strong yellow emission from （pbi）2Ir（acac） and DCJTB, where （pbi）2Ir（acac） plays an important role as a phosphorescent sensitizer for DCJTB. With the blue emitting-layer of N,N＇-diphenyl-N,N＇-bis（1- naphthyl）（1,1＇-biphenyl）-4,4＇-diamine, the codoped system device achieved white emission. The codoped system showed that its Commissions Internationale de 1＇Eclairage coordinates were more independent of the variation of bias voltage than those of phosphorescent doped PVK systems.
基金supported by Beijing Science and Technology Committee (project number D0404003040221)
文摘The coupled DBR LED with one DBR for reflecting normal incidence light and the other for reflecting inclined incidence light has been grown by MOCVD. For improving the conventional DBR which was used to increase light extraction efficiency in AIG-alnP red light LED is analyzed. At 20 mADc injection current, the LED peak wave length is 630 nm, and the light intensity of on axis is 137 mcd. The output light power is 2.32 mW. The light intensity and output light power have been improved compared with the conventional LEDs.
文摘In terms of asymmetrical three-dimensional distribution(ID) of luminous intensity(LI) of light-emitting-diode(LED),a testing system was conducted in this study. Design and principle of the testing system were introduced. 31 photometers were placed on a concentric circle,and all of them were used to gather LI data of LED at the same time. The data acquisition card(DAC) was used to gather multichannel data and controlled motor. Experimental results indicated that the testing system had achieved the goal of testing three-dimensional distribution of LI. And each parameter could meet the requirements of industrial production and measurement.
