Toshihiro Nonaka

Strong light of red up-conversion in a ZnO-TiO 2 composite containing Er 3+ and Yb 3+

The up-conversion (UC) phosphor produced by a metal-organic decomposition (MOD) method has a multifunctional potential for use in applications such as displays and solid-state lighting. ZnO-TiO₂ composite system containing Er³⁺ and Yb³⁺ were prepared by solid state reaction method, and the composite phosphor shows bright red UC emission under 980 nm laser pumping. Two photon process was involved in the UC phenomenon of the Er, Yb:ZnO-TiO₂ phosphor. The effects of heating temperature, ZnO/TiO₂ composition and Er³⁺, Yb³⁺ concentrations on the UC emission behavior were examined. The ZnO-TiO₂ composite product sintered at 900 °C contained Zn₂TiO₄, TiO₂ and RE₂Ti₂O₇ (RE = Er³⁺ and Yb³⁺) phases and exhibited strong red emissions. The maximum emission luminescence of the UC phosphor was obtained when the mixing ratios of the base materials TiO₂ : ZnO and additive materials Yb₂O₃ : Er₂O₃ were 1 : 1 and 0:06 : 0:02, respectively. The ZnO-TiO₂:Er³⁺, Yb³⁺ phosphor was compared to the brightest available phosphor. It suggests that ZnO-TiO₂:Er³⁺, Yb³⁺ is a potential material for the red up-conversion phosphor.

Characteristics of up-conversion phosphor prepared using the MOD method

It is possible to form oxides of many materials by air sintering after coating the substrate with a metal-organic decomposition (MOD) solution, thus enabling the preparation of thin films by means of simple processes such as spin coating. MOD solutions of titanium oxide, zinc oxide, ytterbium oxide, and erbium oxide were used in this study. A mixture of Ti : Zn : Yb : Er was made by mixing the components at an arbitrary ratio, and after coating the substrate with the mixture, the sample was heated in air for 4 h at 1000 °C. The maximum value of the emission luminance of up-conversion (UC) phosphor was obtained when the mixing ratio of the base materials TiO2 : ZnO was 1 : 1. The emission intensity of UC could be controlled by varying the mixing ratio of rare earth content. UC phosphor produced by the MOD method has multifunctional potential such as for displays and solid-state lighting.

Bright yellow up-conversion in a LaOF containing Er 3+ and Yb 3+

LaF₃, metal-oxide system for use as the base material, containing Er³⁺ and Yb³⁺ for host crystal of rare-earth (RE) elements were prepared by solid state reaction method and its upconversion (UC) luminescence excited by 980 nm laser was studied. The effects of firing temperature, LaF3 with Er³⁺, Yb³⁺ concentrations on the UC emission behavior were examined. The LaOF product sintered at ffOO °C contained LaF₃ phases and exhibited strong green and red emissions arising due to the ²H_11/2, ⁴S_3/2→⁴Ii_5/2 and ⁴F_9/2→⁴Ii_5/2 transitions for Er³+ ion, respectively. Bright yellow color by the mixing of green and red colors was observed in the LaOF product doped with 0.01 at.% Er³⁺ and 0.01 at.% Yb³⁺. It suggests that LaOF : Er³⁺, Yb³⁺ is a potential material for the yellow upconversion phosphor.

Luminescence characterization of LaOF:Yb 3+ /Er 3+ up-conversion phosphor

Oxides can be formed from many materials by air sintering after coating a substrate with a metal-organic decomposition (MOD) solution. This enables the preparation of thin films by simple processes such as spin coating. The up-conversion (UC) phosphor produced by the MOD method has a multifunctional potential for use in applications such as displays and solid-state lighting. In this study, a simple LaF3 oxide system was examined for use as the base material and host crystal of rare-earth (RE) elements for UC phosphor. The maximum emission luminescence of the UC phosphor was obtained when the mixing ratios of the base materials LaF3 and additive materials Yb2O3:Er2O3 were 1:0.01:0.01, respectively. When the mixing ratio of the phosphor, LaF:Yb:Er, was 1:0.01:0.01, 550 nm green and 670 nm red emissions were produced. The UC emission intensity could be controlled by varying the mixing ratio of the rare-earth materials.

Optical properties of distributed inorganic EL devices with multi-stripe electrode

In this study, we fabricated distributed inorganic EL device of conventional structure by using multi-stripe Al electrode. We deposited stripe electrode with narrow gaps on a glass substrate and succeeded in achieving the same electric field intensity as conventional structure. When we measured the luminescence from the side of the stripe electrodes, at 150V (frequency : 1.8 kHz), the luminance of electrode sample was 323 cd/m2 to that measured. Electrode transmittance was unnecessary by using the stripe electrodes, and it was possible to produce a display that did not require transparent ITO electrodes. Finally, we simulated the electric field distribution for the inorganic EL using stripe electrodes by semiconductor device simulator Atlas.

Evaluation of distributed-type inorganic electroluminescence devices using comb-shaped electrodes

We deposited comb-shaped metal electrodes with narrow gaps on a glass substrate and succeeded in achieving a high electric field intensity. Using conventional structures, this result could only be achieved by applying transparent electrodes, and in this study, we used a comb-shaped metal (Au) electrode and a comb-shaped indium tin oxide (ITO) electrode. When we measured the luminescence from the opposite side of the comb-shaped electrodes, at 15 V/µm, the luminance in the ITO electrode sample was identical (92–95 cd/m2) to that measured from the side of the comb-shaped electrodes. Conversely, a 111-cd/m2 brightness (a 1.9-fold increase) was observed from the opposite side of the Au electrode. Electrode transmittance was unnecessary when the luminescence was observed from the opposite side of the comb-shaped electrodes, and by using metals such as Au, it was possible to produce a display that did not require transparent electrodes. Finally, we simulated the electric field distribution for the inorganic electroluminescence (EL) using comb-shaped electrodes by semiconductor device simulator Atlas.

Multi-electrode array technologies for distributed-type inorganic EL displays

We deposited comb electrodes with narrow gaps between the teeth on a glass substrate, thus realizing a high electric field intensity that cannot be achieved with conventional structures. Au electrodes are deposited to form a comb shape and then spin-coated with a phosphor layer obtained by mixing ZnS phosphor particles with resins in a certain ratio. An AC voltage was applied to the gaps between the teeth of the comb electrode to emit light, from which the luminance was measured for different electric field intensities. The luminance was not affected by the transmittance of the electrodes themselves when measured from the phosphor layer side. Therefore, it may be possible to produce a display that does not require transparent electrodes.

Characteristics of distributed-type inorganic electroluminescence panels with comb-shaped electrodes

We deposited comb electrodes with narrow gaps between the teeth on a glass substrate, thus realizing a high electric field intensity that cannot be achieved with conventional structures. Au electrodes are deposited to form a comb shape and then spin-coated with a phosphor layer obtained by mixing ZnS phosphor particles with resins in a certain ratio. An AC voltage was applied to the gaps between the teeth of the comb electrode to emit light, from which the luminance was measured for different electric field intensities. The luminance was not affected by the transmittance of the electrodes themselves when measured from the phosphor layer side. Therefore, it may be possible to produce a display that does not require transparent electrodes by using the phosphor layer side of a device with comb electrodes made of metals, such as Au, for the display.