| Recently, the research of organic electroluminescent materials and devices is the frontier fields of science which is developing rapidly. The organic electroluminescent devices(OLEDs) have a broad application prospect. The organic electroluminescent device is a light emitting device which is fabricated by a multilayer organic film with low driving voltage, high brightness and luminous efficiency and fast response speed. It can be produced in a large scale. It has been developed rapidly in the last few years. The flat panel display that is built by the organic electroluminescent devices has many advantages such as wide viewing angle, simple manufacturing process and low cost. It can also achieve the flexible display. It is widely believed to be the mainstream of a new generation of display devices. Also, there has been a growing interest in OLEDs that emit in the near infrared (NIR) region (700-2500nm). Potential applications of these NIR electroluminescent devices are particularly interesting for optical communication(1300-1600nm), thermal imaging(≥1500nm) and biological imaging. A variety of organic and organometallic materials have been studied for NIR electroluminescence (EL).In this paper, a polymer light-emitting diode with inverted structure was processed by spin coating and vacuum deposition method. The basic structure of the device was ITO/ZnO (30nm)/PFO:MEH-PPV(100nm)/MoO3(8nm)/Al. Because of the introduction of the electron injection layer, the combination of the electron and hole in the emission layer enhanced greatly, which improved the luminescent properties of the device. And the inverted structure improved the stability of the device. The optical and electrical characteristics of the device were characterized by the current-voltage (I-V) curve, absorption spectrum and photoluminescence spectrum. The device exhibited typical diode characteristics. The forward threshold voltage was about3V.Also, near-infrared electroluminescent device is demonstrated by employing the C60-dopped4,4’-N,N’-dicarbazole-biphenyl (CBP) as the emitting layer. The device structure is indium-tin-oxide (ITO)/N, N’-di-1-naphthyl-N, N’-diphenylbenzidine (NPB)/CBP:C60/2,9-dimethyl-4,7diphenyl-1,10-phenanthroline (BCP)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Al. A dominant peak at910nm and a shoulder at1100nm are observed in the electroluminescence (EL) spectrum at room temperature. The results suggest that charge trapping plays a dominant role in the NIR EL mechanisms, whereas the energy transfer from CBP to C6o plays a minor one. The EL spectrum of C6o doped CBP shows a red shift of about200nm compared with that of C60-doped PMMA. The different experimental results for C60-doped PMMA and C60-doped CBP are discussed. The results indicate that the C6o’s luminescence spectrum can be controlled by changing the surrounding environments and the aggregate states of the C6o molecule.In the end, near-infrared (NIR) organic light-emitting devices (OLEDs) are demonstrated by employing erbium fluoride (ErF3)-doped tris-(8-hydroxyquinoline) aluminum (Alq3) as the emitting layer. The device structure is ITO/N, N’-di-l-naphthyl-N, N’-diphenylbenzidine (NPB)/Alq3:ErF3/2,2’,2"-(1,3,5-phenylene) tris (1-phenyl-lH-benzimidazole)(TPBI)/Alq3/Al. Room-temperature electroluminescence around1530nm is observed due to4I13/2-4I15/2transition of the Er3+. The full width at half maximum (FWHM) of the electroluminescent (EL) spectrum is～50nm. The NIR EL intensity from the ErF3-based device is～4times higher than that of Er(DBM)3Phen-based device at the same current. Alq3-ErF3composite films are investigated by the measurements of X-ray diffraction (XRD), absorption, photoluminescence (PL), and PL decay time, respectively. Electron-only devices are also fabricated. The results indicate that energy transfer mechanism and charge trapping mechanism coexist in the NIR EL process. |
PDF Full Text Request