[Investigation of luminescence mechanism of hybrid MEH-PPV/ SiO2 and super liner characteristic of amorphous SiO2].

For electricity induced luminescence of thin film, the heterojunction luminescence devices were produced by compounding the organic polymer of MEH-PPV and inorganic semiconductor SiO2. Utilizing the super liner characteristic of SiO2 as acceleration, multiplication and ionization, the solid-state cathodoluminescence was realized. The obvious feature of electroluminescence in the luminescence device with ITO/SiO2/MEH-PPV/SiO2/Al is that it has two spectral bands. In the electroluminescence spectra, the authors obtained both blue emission (403 nm)and excition luminescence (583 nm) of MEH-PPV and the intensity of the long and short wave peak changing with the voltage. Only long wave peak is observed when the voltage is low and only short wave peak appears when the voltage is high. It is the typical feature that the solid-state cathodoluminescence has two spectral bands. It is a new light emission, which has new mechanism and is important for the luminescence. One of the important aspects of the solid state cathodoluminescence theory is the super liner characteristic of SiO2. In the present paper, the luminescence dynamics of solid-state cathodoluminescence, the super liner characteristic of SiO2 in the higher electric field and the influences of thickness on it were studied.

[Phosphorescent effect of Ir (ppy)3 on the luminescent characteristic of Rubrene].

Many organic matters including heavy metal ions can validly utilize the singlet and triplet for luminescence owiog to the spin-orbit coupling. As a result, the internal quantum efficiency can easily achieve a value higher than traditional organic light emitting diodes in theory. There is a strong luminescence of PVK in PVK : PBD : Rubrene system. PL spectra excited by 345 nm of PVK : PBD : Rubrene thin film has a 410 nm PVK luminescent peak and a 560 nm Rubrene peak. EL still has a PVK luminescent peak, which should be kept from happening. Excitons can not adequately transferred from the matrix solution to Rubrene. The doping with Ir(ppy)3 improves the PVK : PBD : Rubrene system performance. PL spectra excited by 345 nm of PVK : PBD : Ir(ppy)3 : Rubrene with low concentration of Rubrene has a 510 nm Ir(ppy)3 peak and a new 548 nm one. However, the Ir(ppy)3 peak is smaller and the Rubrene one is bigger in EL spectra. Notably a strong and single luminescence of Rubrene is obtained in EL and PL spectra excited by 345 nm of PVK : PBD : Ir(ppy)3 : Rubrene with high concentration of Rubrene. Meanwhile, the Ir(ppy)3 luminescent peak disappears. The mechanism originates from the phosphorescent effect of Ir (ppy)3. The singlet excitons can basically be transferred from PVK : PBD or Ir(ppy)3 to Rubrene. But most excitons from Ir (ppy)3 can directly tunnel to the fluorescent material and come into being singlet states that can return to ground states and cause luminescence. Rubrene can accept proportional excitons with low concentration. While the concentration of Rubrene is higher, excitons can be entirely accepted by Rubrene. The effect also restricts the luminescent intensity of Ir(ppy)3 and boosts up that of Rubrene. Furthermore, the energy transfer in PVK : PBD : Ir(ppy)3 : Rubrene system is primary the Forester energy transfer. Excitation spectra of Rubrene and emission spectra of Ir(ppy)3 have a large overlap revealing that there is a strong energy transfer and further confirmed the phosphorescent effect of Ir(ppy)3. The doping system with phosphorescence material and small molecules can enhance the brightness and internal quantum efficiency.