Yoshinobu Miyamoto

Luminescence Properties of ( Sr1 − u Ba u ) Si2O2N2 : Eu2 + , Yellow or Orange Phosphors for White LEDs, Synthesized with ( Sr1 − u Ba u ) 2SiO4 : Eu2 + as a Precursor

Luminescence properties and formation process of (Sr 1-u Ba u )Si 2 O 2 N 2 :Eu 2+ , phosphors suitable for white light-emmitting (LEDs), were investigated. These phosphors were synthesized by a method using (Sr 1-u Ba u ) 2 SiO 4 :Eu 2+ as a precursor instead of simple oxides. Compared with a conventional solid-state reaction method, this method provides increased luminescence efficiency. X-ray diffraction analysis has indicated that transformation of low-temperature type (Sr 1-u Ba u )Si 2 O 2 N 2 :Eu 2+ to high-temperature type, which has a higher luminescence efficiency, occurs with a higher probability when (Sr 1-u Ba u ) 2 SiO 4 :Eu 2+ is used as a precursor. Under 460 nm excitation, (Sr 1-u Ba u )Si 2 O 2 N 2 :Eu 2+ shows an emission band peaked at 550-590 nm for varied Ba fraction u. This series of materials shows the high integrated photoluminescence intensity at u = 0.25-0.75. Particularly, at u = 0.5, it shows the highest quantum output, which is about 1.2 times as high as that of the commercial yellow phosphor, (Y,Gd) 3 Al 5 O 12 :Ce 3+ , P46-Y3. The internal quantum efficiency is estimated to be about 80% for samples of u = 0.5 and 0.75. The high efficiency and small thermal quenching allow these materials to be applied to white LEDs.

Photoluminescence characteristics of Pb-doped, molecular-beam-epitaxy grown ZnSe crystal layers

The characteristic green photoluminescence emission and related phenomena in Pb-doped, molecular-beam-epitaxy (MBE)-grown ZnSe crystal layers were investigated to explore the nature of the center responsible for the green emission. The intensity of the green emission showed a distinct nonlinear dependence on excitation intensity. Pb-diffused polycrystalline ZnSe was similarly examined for comparison. The characteristic green emission has been observed only in MBE-grown ZnSe crystal layers with moderate Pb doping. The results of the investigations on the growth conditions, luminescence, and related properties of the ZnSe crystal layers suggest that the green emission is due to isolated Pb replacing Zn and surrounded with regular ZnSe lattice with a high perfection.

Photoluminescence characteristics of Sn-doped, molecular-beam-epitaxy-grown ZnSe crystal layers

A novel, distinct blue photoluminescence emission peaking at a 490 nm wavelength has been observed in Sn-doped, molecular-beam-epitaxy-grown ZnSe crystal layers at low temperatures, which bears characteristics analogous to those of the green emission previously reported in Pb-doped ZnSe crystal layers. The blue emission appears in Sn-doped crystal layers having good crystallographic quality and cannot be observed in the crystal layers with inferior quality. The blue emission shows a superlinear dependence on the excitation intensity. Discussions are presented on the nature of the blue emission due to Sn, particularly in conjunction with that of the green emission in Pb-doped ZnSe crystal layers.