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Intrinsic Polarization and Tunable Color of Electroluminescence from Organic Single Crystal-based Light-Emitting Devices.

Ding R, Feng J, Zhou W, Zhang XL, Fang HH, Yang T, Wang HY, Hotta S, Sun HB - Sci Rep (2015)

Bottom Line: A single crystal-based organic light-emitting device (OLED) with intrinsically polarized and color-tunable electroluminescence (EL) has been demonstrated without any subsequent treatment.The polarization ratio of 5:1 for the transversal-electric (TE) and transversal-magnetic (TM) polarization at the emission peak of 575 nm, and 4.7:1 for the TM to TE polarization at the emission peak of 635 nm, respectively, have been obtained.The emitting color is tunable between yellow, yellow-green and orange by changing the polarization angle.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun, 130012, People's Republic of China.

ABSTRACT
A single crystal-based organic light-emitting device (OLED) with intrinsically polarized and color-tunable electroluminescence (EL) has been demonstrated without any subsequent treatment. The polarization ratio of 5:1 for the transversal-electric (TE) and transversal-magnetic (TM) polarization at the emission peak of 575 nm, and 4.7:1 for the TM to TE polarization at the emission peak of 635 nm, respectively, have been obtained. The emitting color is tunable between yellow, yellow-green and orange by changing the polarization angle. The polarized EL and the polarization-induced color tunability can be attributed to the anisotropic microcavity formed by the BP3T crystal with uniaxial alignment of the molecules.

No MeSH data available.


(a) A sketch of the experimental setup for the optical measurements, the observation angle variation is the angle to the normal of the sample (c-axis of the crystal) in the angle-resolved EL spectra measurement. (b) Angle-resolved EL spectra of BP3T single-crystal OLEDs by mounting the samples on a rotating holder. (c) Polarization angle-resolved EL spectra detected at normal incidence by varying the polarization direction.
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f4: (a) A sketch of the experimental setup for the optical measurements, the observation angle variation is the angle to the normal of the sample (c-axis of the crystal) in the angle-resolved EL spectra measurement. (b) Angle-resolved EL spectra of BP3T single-crystal OLEDs by mounting the samples on a rotating holder. (c) Polarization angle-resolved EL spectra detected at normal incidence by varying the polarization direction.

Mentions: In order to clarify the mechanism of this polarized light emission, the optical measurement system is set up for the observation angle-resolved and polarization angle-resolved EL spectra. The experiment setup is shown in Fig. 4a. The observation angle-resolved EL spectra are measured by rotating the observation angle to the c-axis of the crystal without polarizer. With the increasing of the observation angle from 0° to 60°, both emitting peaks centered at 575 nm and 635 nm shift towards short wavelength (Fig. 4b). The peak at the short wavelength moves out of the emission wavelength region of the crystal and disappears, when the observation angle is increased to 30°. On the basis of the template stripping technique, the anode and cathode of Au and Ca/Ag serving as reflecting mirrors are deposited on both sides of the organic single crystal. Then an anisotropic microcavity is therefore established by sandwiching the crystal between the metallic electrodes. Therefore, the blue shift of the emission peaks is caused by the microcavity effect. In the case of the polarization angle-resolved EL spectra (Fig. 4c) detected by varying the polarization direction of the polarizer, the polarization angle corresponds to the angle between the collection polarizer and the centre axis which is parallel to the OLEDs. By the rotation of the polarizer, the EL spectra can be changed from orange to yellow-green and yellow. The polarized EL and tunable emission color from the BP3T-based OLEDs can be attributed to the large birefringence difference between a-axis and b-axis of the crystal induced by the uniaxially alignment of the BP3T molecules4243444546. The two EL peaks at 575 and 635 nm observed in the TE and TM polarized spectra correspond to the resonance of TE and TM modes in the anisotropic microcavity, respectively474849. The TE and TM cavity modes exhibit a giant polarization splitting of around 60 nm which is much broader than the BP2T crystal-based OLEDs16. The polarization splitting is broad enough to tune the color emission from yellow-green to orange observed from the OLED due to a big difference of the refractive index between a-axis and b-axis of BP3T single crystals. There is also a giant polarization splitting observed from the polarized PL spectra measured with the crystal-based OLEDs (Supplementary Figure S3). Furthermore, the resonant wavelength in the microcavity will be determined by the total optical length depending on the thickness of crystals16. A comparison of different polarized EL spectra based on different crystal thickness is shown in the Supplementary Figure S4. The two cavity peaks will shift towards short wavelength when the thickness of crystals employed in the OLEDs decreases from 510 to 500 nm.


Intrinsic Polarization and Tunable Color of Electroluminescence from Organic Single Crystal-based Light-Emitting Devices.

Ding R, Feng J, Zhou W, Zhang XL, Fang HH, Yang T, Wang HY, Hotta S, Sun HB - Sci Rep (2015)

(a) A sketch of the experimental setup for the optical measurements, the observation angle variation is the angle to the normal of the sample (c-axis of the crystal) in the angle-resolved EL spectra measurement. (b) Angle-resolved EL spectra of BP3T single-crystal OLEDs by mounting the samples on a rotating holder. (c) Polarization angle-resolved EL spectra detected at normal incidence by varying the polarization direction.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4513548&req=5

f4: (a) A sketch of the experimental setup for the optical measurements, the observation angle variation is the angle to the normal of the sample (c-axis of the crystal) in the angle-resolved EL spectra measurement. (b) Angle-resolved EL spectra of BP3T single-crystal OLEDs by mounting the samples on a rotating holder. (c) Polarization angle-resolved EL spectra detected at normal incidence by varying the polarization direction.
Mentions: In order to clarify the mechanism of this polarized light emission, the optical measurement system is set up for the observation angle-resolved and polarization angle-resolved EL spectra. The experiment setup is shown in Fig. 4a. The observation angle-resolved EL spectra are measured by rotating the observation angle to the c-axis of the crystal without polarizer. With the increasing of the observation angle from 0° to 60°, both emitting peaks centered at 575 nm and 635 nm shift towards short wavelength (Fig. 4b). The peak at the short wavelength moves out of the emission wavelength region of the crystal and disappears, when the observation angle is increased to 30°. On the basis of the template stripping technique, the anode and cathode of Au and Ca/Ag serving as reflecting mirrors are deposited on both sides of the organic single crystal. Then an anisotropic microcavity is therefore established by sandwiching the crystal between the metallic electrodes. Therefore, the blue shift of the emission peaks is caused by the microcavity effect. In the case of the polarization angle-resolved EL spectra (Fig. 4c) detected by varying the polarization direction of the polarizer, the polarization angle corresponds to the angle between the collection polarizer and the centre axis which is parallel to the OLEDs. By the rotation of the polarizer, the EL spectra can be changed from orange to yellow-green and yellow. The polarized EL and tunable emission color from the BP3T-based OLEDs can be attributed to the large birefringence difference between a-axis and b-axis of the crystal induced by the uniaxially alignment of the BP3T molecules4243444546. The two EL peaks at 575 and 635 nm observed in the TE and TM polarized spectra correspond to the resonance of TE and TM modes in the anisotropic microcavity, respectively474849. The TE and TM cavity modes exhibit a giant polarization splitting of around 60 nm which is much broader than the BP2T crystal-based OLEDs16. The polarization splitting is broad enough to tune the color emission from yellow-green to orange observed from the OLED due to a big difference of the refractive index between a-axis and b-axis of BP3T single crystals. There is also a giant polarization splitting observed from the polarized PL spectra measured with the crystal-based OLEDs (Supplementary Figure S3). Furthermore, the resonant wavelength in the microcavity will be determined by the total optical length depending on the thickness of crystals16. A comparison of different polarized EL spectra based on different crystal thickness is shown in the Supplementary Figure S4. The two cavity peaks will shift towards short wavelength when the thickness of crystals employed in the OLEDs decreases from 510 to 500 nm.

Bottom Line: A single crystal-based organic light-emitting device (OLED) with intrinsically polarized and color-tunable electroluminescence (EL) has been demonstrated without any subsequent treatment.The polarization ratio of 5:1 for the transversal-electric (TE) and transversal-magnetic (TM) polarization at the emission peak of 575 nm, and 4.7:1 for the TM to TE polarization at the emission peak of 635 nm, respectively, have been obtained.The emitting color is tunable between yellow, yellow-green and orange by changing the polarization angle.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun, 130012, People's Republic of China.

ABSTRACT
A single crystal-based organic light-emitting device (OLED) with intrinsically polarized and color-tunable electroluminescence (EL) has been demonstrated without any subsequent treatment. The polarization ratio of 5:1 for the transversal-electric (TE) and transversal-magnetic (TM) polarization at the emission peak of 575 nm, and 4.7:1 for the TM to TE polarization at the emission peak of 635 nm, respectively, have been obtained. The emitting color is tunable between yellow, yellow-green and orange by changing the polarization angle. The polarized EL and the polarization-induced color tunability can be attributed to the anisotropic microcavity formed by the BP3T crystal with uniaxial alignment of the molecules.

No MeSH data available.