Study of the Triplet and Singlet States of Ir(ppy)_3 by the Excitation Spectra for Photoluminescence

Photoluminescence of phosphorescent molecule tris(2-phenylpyridine) iridium (Ir(ppy)_3) has been studied in the neat film and film of Ir(ppy)_3 doped in CBP. Weak absorption bands at 485, 451 and 406 nm are attributed to the metal-ligand charge transfer triplet state (3MLCT) from the excitation spectra for the green emission. Additional emission band with a peak at 396 nm and a broad sideband at about 423 nm are observed in the neat film. The 396 nm emission is much weaker than the green emission. Its intensity increases with decreasing temperature from 300 K to about 100 K, and becomes constant at 100-10 K. This emission is attributed to the emission from the singlet state 1MLCT which gives rise to absorption band at 386 nm. The conversion of the intersystem crossing from the singlet state to the triplet state is estimated to be 98.7%. From difference of excitation spectra between the films doped and non-doped in CBP, we suggest energy transfer from the n = 1 vibrational state of Ir(ppy)_3 dopant to the n = 0 vibrational state of CBP host. Discussion is given on the vibronic structure observed in the emission and excitation spectra by comparing with the observed Raman spectrum

Relaxation and luminescence processes in photo-excited phosphorescent Pt^<2+> -compound N^N^C-Pt(Cl)

　Numerical analysis is made for the photoluminescence (PL) lifetime and intensity of cyclometalated Pt-compound N^N^C-Pt(Cl), by taking into account non-radiative relaxations among three zero-field splitting substates of triplet T_1 state and energy dissipation from the substates to unexcited neighboring N^N^C-Pt(Cl) and by solving the rate equations for the three substates. From the fitting between the calculated and observed temperature dependences of PL lifetime and intensity, large zero-field splitting of 90cm and short radiative lifetime of 1.9 μs were obtained. It is suggested that the energy dissipation is responsible for the decrease of PL intensity with increasing temperature

Analysis on Phosphorescence Decay Time of Ir(ppy)_3 in Tetrahydrofuran under Magnetic Field

　The photoluminescence (PL) lifetime of fac tris(2-phenylpyridine) iridium (Ir(ppy)_3) in tetrahydrofuran has been observed to decrease from 145 to 47 µs at 1.5 K with increasing the magnetic field B from 0 to 10 T. A numerical analysis has been done to explain the magnetic field dependence of the PL lifetime. We use a model of three substates 1, 2 and 3 for the emitting 3MLCT triplet states, where non-radiative one-phonon relaxation is undertaken, and assume the magnetic interaction between the low-energy substates 1 and 2 and neglect the interaction with the upper substates 3. Three PL lifetimes are derived. Good agreement is obtained between the observed PL lifetime and the calculated longest PL lifetime, including the deviation from the B^2 dependence observed above about 6 T. The field dependence is also calculated at various temperatures up to 300 K. Unlike the case of 1.5 K, the PL lifetimes change little at high temperatures

Europium ions in electrolytic colored KCl:Pb^<2+> + Eu^<2+> crystals

　The crystals of KCl doped with Pb^ and Eu^ ions were electrolytically colored at low temperature such as 300℃ and high electric field of 4000 V/cm. The absorption, magnetic circular dichroism and photoemission spectra were studied for the crystals before and after the coloration, and compared with those of colored KCl crystals doped with Pb^ and Ca^ , Sr^ ions. It is concluded that Eu^ ions do not change the valency by the coloration. Broad infrared emission bands are observed at 1200, 1450 and 1985 nm in the electrolytically colored crystal.　PACS: 76.30 Mi; 76.30 Kg; 78.35 F

Level Assignment for Various Photoluminescence Bands of Tm^<3+> Ions in LiYF_4 Crystal

　Photoluminescence and excitation spectra of Tm ions in LiYF_4 crystal have been investigated at 12 K. The luminescence is investigated under excitation with lights of 780, 680, 460, 360 and 266 nm wavelengths. The emission bands are observed to depend on the excitation wavelength, e.g. two emission bands at 1229 and 1201 nm are generated by the 460 nm excitation but not by 780, 680, 360 and 266 nm excitation. Comparing the emission spectra with the excitation spectra for the IR and visible emissions, we suggest the level assignment for the observed luminescence bands including the 288 and 286 nm UV emission bands

Spectroscopic and electrical characteristics of highly stable ultra-violet emitting tetraphenylsilane-carbazole organic compound

　Optical absorption and photoluminescence (PL) are investigated for organic small molecule of ultra-violet (344 nm) fl uorescence emitting bis (3,5-di (9H-carbazol-9-yl) phenyl)diphenylsilane(SimCP2), together with the glass transition temperature T_g and carrier mobility. SimCP2 is morphologically more stable than the other ultra-violet light emitting materials 1,3-bis (9-carbazolyl) benzene (mCP) and 3,5-bis (9-carbazolyl) tetraphenylsilane (SimCP) because of higher T_g of 148 °C. The electron and hole mobilities are higher (4.8 × 10^＜－4＞ and 2.7 × 10^＜－4＞cm^2V^＜－1＞s^＜－1＞, respectively,　at electric field of 9 × 10^4Vcm^＜－1＞) than those of mCP and SimCP. From the PL spectra of SimCP2 doped in polystyrene, the most intense 0-0 vibrational T_1 emission band was observed at 412 nm. SimCP2 has a wide band gap of highest occupied molecular orbital (HOMO) energy of 6.12 eV and lowest unoccupied molecular orbital (LUMO) energy of 2.56 eV. These results indicate that SimCP2 is expected to be effi cient host material for blue phosphorescence emitters in organic light emitting diodes

Enhancement of Efficiency and Lifetime of Blue Organic Light-Emitting Diodes Using Two Dopants in Single Emitting Layer

We have demonstrated efficient blue organic light-emitting diode with the structure of indium tin oxide/4,4′,4″-tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine/1,4-bis[N-(1-naphthyl)-N′-phenylamino]-4,4′-diamine/9,10-di(2-naphthyl)anthracene (ADN): 1-4-di-[4-(N,N-di-phenyl)amino]styryl-benzene (DSA-ph) 3 wt%/tris-(8-hydroxyquinoline)aluminum/LiF/Al. Improved efficiencies and longer operational lifetime were obtained by codoping a styrylamine-based dopant BD-3 (0.1 wt%) into the emitting layer of ADN doped with DSA-ph compared to the case of non-codoping. This was due to the improved charge balance and expansion of exciton recombination zone. The better charge balance was obtained by reducing the electron mobility of ADN which was higher than the hole mobility in the case of non-codoping