Po-Ching Kao

Energy Transfer and Thermal Quenching Behaviors of CaLa2 ( MoO4 ) 4 : Sm3 + , Eu3 + Red Phosphors

CaLa 2 (MoO 4 ) 4 :Sm 3+ , Eu 3+ phosphors are prepared using a convenient solid-state reaction route. The red emission intensity of Eu 3+ is enhanced by Sm 3+ ion codoping. The energy transfer mechanism from Sm 3+ to Eu 3+ was found to be a dipole-quadrupole interaction with a critical distance of 10.42 A. With increasing Eu 3+ doping content, the energy transfer efficiency (Sm 3+ → Eu 3+ ) gradually increased to 75.5%. The thermal quenching behavior was investigated using absorption and emission spectra. The thermal quenching temperature (T 50 ) of CaLa 2 (MoO 4 ) 4 :Sm 3+ ,Eu 3+ phosphors is above 200°C, and the activation energy of the thermal quenching process is 0.13 eV. The effect of codoped Sm 3+ ions on the thermal stability of CaLa 2 (MoO 4 ) 4 :Sm 3+ ,Eu 3+ phosphors is investigated.

How the surface energy of ultra-thin CuF2 film as anode buffer layer affect the organic light-emitting devices?

The effect of surface energy on organic light-emitting device performance was demonstrated by depositing an ultra-thin CuF2 buffer layer on indium tin oxide (ITO) substrates, followed by ultraviolet (UV)-ozone treatment. An optimal thickness UV-ozone treated CuF2 (4 nm)/ITO anode significantly improved device performance. Work function estimates from X-ray photoelectron measurements suggested that both pristine and UV-ozone treated CuF2/ITO anodes had no hole injection barrier. Measurements of energy band, surface energy and surface polarity indicated device improvement came from the simultaneous increase in work function and surface energy of ITO by adding treated CuF2 film between ITO and the hole-transporting layer.

Enhanced luminescence efficiency of Ag nanoparticles dispersed on indium tin oxide for polymer light-emitting diodes

This study presents a substantial enhancement in electroluminescence achieved by depositing Ag nanoparticles on an ITO-coated glass substrate (Ag/ITO) for approximately 10-s to form novel window materials for use in polymer light-emitting diodes (PLEDs). The PLEDs discussed herein are single-layer devices based on a poly[9,9-dioctylfluorene-co-benzothiadiazole] (F8BT) emissive layer. In addition to its low cost, this novel fabrication method can effectively increase the charge transport properties of the active layer to meet the high performance requirements of PLEDs. Due to the increased conductivity and work function of the Ag/ITO substrate, the electroluminescence intensity was increased by nearly 3.3-fold compared with that of the same PLED with a bare ITO substrate.

High PLED Enhancement by Surface Plasmon Coupling of Au Nanoparticles

In this investigation, a simple, rapid, and low-cost sputtering system was employed to deposit a Au-nanoparticles (Au-NPs) layer in polymer light-emitting diode (PLED) at room temperature. The green-emitting PLEDs considered herein are single-layer devices based on a poly[9,9-dioctylfluorene-co-benzothiadiazole] emissive layer. This novel fabrication effectively avoids interruption or degradation of the charge transport properties of the active layer and therefore satisfies the high performance requirements for PLEDs. Because of the surface-plasmon-enhanced emission, the electroluminescence intensity of the green-emitting PLED based on the Au-NPs/ITO anode increased nearly 2.7-fold, compared to that of the standard green-emitting PLED with a bare ITO substrate.

The effects of ultraviolet-ozone-treated ultra-thin MnO-doped ZnO film as anode buffer layer on the electrical characteristics of organic light-emitting diodes

In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing an MnO-doped ZnO film as a buffer layer between the indium tin oxide (ITO) electrode and the α-naphthylphenylbiphenyldiamine hole transport layer. The enhancement mechanism was systematically investigated, and the X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results revealed the formation of the UV-ozone-treated MnO-doped ZnO film. With this film, the work function increased from 4.8 eV (standard ITO electrode (∼ 10±5 Ω/◻)) to 5.27 eV (UV-ozone-treated MnO-doped ZnO deposited on the ITO electrode with 1 wt. % for 1 nm), while the surface roughness of the UV-ozone-treated MnO-doped ZnO film was smoother than that of the ITO electrode. The deposited UV-ozone-treated MnO-doped ZnO film increased the surface energy and polarity of the ITO surface, as determined from contact angle measurements. Further, results from admittance spectroscopy showed that the inserted UV-ozone-treated Mn...

Influence of gallium-doped zinc-oxide thickness on polymer light-emitting diode luminescence efficiency.

Conducting atomic force microscopy and scanning surface potential microscopy were used to study the local electrical properties of gallium‐doped zinc oxide (GZO) films prepared by pulsed laser deposition (PLD) on a polyimide (PI) substrate. For a PLD deposition process time of 8 min, the root‐mean‐square roughness, coverage percentage of the conducting regions, and mean work function on the GZO surface were 2.33 nm, 96.6%, and 4.82 eV, respectively. When the GZO/PI substrate was used for a polymer light‐emitting diode (PLED), the electroluminescence intensity increased by nearly 20% compared to a standard PLED, which was based on a commercial‐ITO/glass substrate. Microsc. Res. Tech. 76:783–787, 2013.

2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate as an effective electron injecting interlayer on indium-tin oxide cathode in inverted bottom-emission organic light-emitting diodes

2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate (MADN:Rb2CO3) is used as an effective electron injecting interlayer on an indium-tin oxide (ITO) cathode for inverted bottom-emission organic light-emitting diodes (IBOLEDs). At a Rb2CO3 doping concentration of 20% in MADN, the device exhibits enhanced characteristics, some of which are turn-on voltage, luminance at a given current density, and current efficiency. The attained performance is better than that of the device using lithium fluoride (LiF) as an n-type dopant. Space-charge-limited current acknowledges improved electrical properties of Rb2CO3 doped MADN. Ultraviolet and X-ray photoelectron spectroscopy investigation unveils an interfacial dipole layer induced by charge transfer between Rb2CO3 and ITO, leading to a lowered ITO work function and an electron injection barrier. The improved electron injection and transport capabilities contribute to better charge balance in IBOLED, thus resulting in advanced luminance efficiency. In addition, the morphology stability of organic films is also amended, which benefits long-term reliability under operationally induced thermal stress. Moreover, the effectiveness of using Rb2CO3:MADN as an electron injecting layer for IBOLEDs is superior to many of its alkali-based counterparts demonstrated in the literature, with high compatibility with different types of sophisticated ITO-based IBOLEDs.2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate (MADN:Rb2CO3) is used as an effective electron injecting interlayer on an indium-tin oxide (ITO) cathode for inverted bottom-emission organic light-emitting diodes (IBOLEDs). At a Rb2CO3 doping concentration of 20% in MADN, the device exhibits enhanced characteristics, some of which are turn-on voltage, luminance at a given current density, and current efficiency. The attained performance is better than that of the device using lithium fluoride (LiF) as an n-type dopant. Space-charge-limited current acknowledges improved electrical properties of Rb2CO3 doped MADN. Ultraviolet and X-ray photoelectron spectroscopy investigation unveils an interfacial dipole layer induced by charge transfer between Rb2CO3 and ITO, leading to a lowered ITO work function and an electron injection barrier. The improved electron injection and transport capabilities contribute to better charge balance in IBOLED, thus resulting in advanced luminance efficiency. ...

Differences between the luminescence efficiencies of PLEDs based on Ag-nanoparticles/GZO/PEN and GZO/Ag-nanoparticles/PEN anodes

This study presents a simple, rapid, and low-cost sputtering system for the deposition of Ag-nanoparticles (Ag-NPs) in polymer light-emitting diodes (PLEDs) at room temperature. Proposed PLED structures based on Ag-NPs/GZO/PEN (AGP) and GZO/Ag-NPs/PEN (GAP) anodes are discussed. Because of surface-plasmon-enhanced emission, the electroluminescence intensities of PLEDs based on AGP anodes increased nearly 3.4-fold compared to normal PLEDs without Ag-NPs.