Haruki Fukada

Photoluminescence and electroluminescence from Eu-activated CaAl2O4-based multicomponent oxide thin-film phosphors

Photoluminescence (PL) and electroluminescence (EL) from newly developed Eu-activated CaAl2O4 -based multicomponent oxide phosphor thin films prepared by rf magnetron sputtering are described. Yellowish green and blue emissions in PL were obtained in as-deposited and postannealed ((CaAl2O4)1−x–(BaAl2O4)x):Eu and ((CaAl2O4)1−x–(MgAl2O4)x):Eu thin films, respectively. In addition, blue emission in EL was observed from thin-film electroluminescent (TFEL) devices fabricated by using ((CaAl2O4)1−x–(BaAl2O4)x):Eu thin films postannealed at 1000°C in an Ar+H2(5%) gas atmosphere. A luminance of 3.2cd∕m2 for blue emission was obtained in a ((CaAl2O4)0.44–(BaAl2O4)0.56):Eu TFEL device driven by a 1kHz sinusoidal wave ac voltage; the blue EL emission corresponds to the CIE color coordinates of (x=0.24, y=0.13).

Carrier dynamics studies of III-nitride materials using photo-acoustic and photoluminescence measurements

Internal quantum efficiency (IQE) of radiative recombination for photo-excited carriers in compound semiconductor materials is usually estimated from temperature dependence of photoluminescence (PL) intensity by assuming that the IQE at cryogenic temperature is unity. III-nitride semiconductors, however, usually have large defect-density, and the assumption is not necessarily valid. In this study, we developed a new method to estimate accurate IQE values by simultaneous PL and photo-acoustic (PA) measurements, and demonstratively evaluated the IQE values for an InGaN quantum-well sample. The results show that the conventional method cannot give accurate IQE values, and that our method is a promising way for accurate estimation of absolute IQE values, which could lead to the accurate estimation of radiative and nonradiative recombination lifetimes in carrier dynamics studies.

Luminescent characteristics in blue-emitting bi-activated multi-component oxide phosphor thin films

Recently, blue emission in cathodoluminescence (CL) and photoluminescence (PL) from Bi-activated oxide phosphors such as LaInO<inf>3</inf>:Bi, YNbO<inf>4</inf>:Bi and GdNbO<inf>4</inf>:Bi has been reported. Although the absorption and emission transitions of phosphors activated by ions with ns² configuration (e.g., Bi³⁺-activated phosphors) have been extensively investigated, there are few reports on the luminescent characteristics of Bi-activated oxide phosphor thin films. A blue emission in PL and electroluminescence (EL) from newly developed Bi-activated oxide phosphor thin films, such as La<inf>2</inf>O<inf>3</inf>:Bi and LaInO<inf>3</inf>:Bi, has been recently reported [1,2]. In this paper, we describe the luminescent characteristics of newly developed blue-emitting Bi-activated multi-component oxide phosphor thin films using La<inf>2</inf>O<inf>3</inf>-Y<inf>2</inf>O<inf>3</inf>, Y<inf>2</inf>O<inf>3</inf>-Gd<inf>2</inf>O<inf>3</inf> or Gd<inf>2</inf>O<inf>3</inf>-La<inf>2</inf>O<inf>3</inf>, which are composed of various combinations of La<inf>2</inf>O<inf>3</inf>, Y<inf>2</inf>O<inf>3</inf> and Gd<inf>2</inf>O<inf>3</inf>, as the host material.