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 ͑LEDs͒, 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,Gd͒ 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.
An orange-emitting, long-persistent phosphor,
Ca2Si5normalN8:Eu2+,Tm3+
, was developed. Afterglow of this phosphor decays more slowly than that of the conventional red-emitting, long-persistent phosphor,
normalY2normalO2S:Eu3+,Ti,Mg
. After 420 nm excitation, the afterglow luminance is initially lower, but, after 8 min, gets higher than luminance of
normalY2normalO2S:Eu3+,Ti,Mg
. Long afterglow results from electron traps formed by
Tm3+
at the
Ca2+
site. The origin of two main thermoluminescence glow peaks at 220 and 350 K is discussed based on their dependence on Eu or Tm concentration and Ca/Si atomic ratio. Increased thermoluminescence intensity is observed by excitation in
Eu2+
4f-5d transition at room temperature followed by the fundamental absorption of the host at low temperature.
Emissive liquid crystal display (e-LCD) panels consisting of 405 nm near-UV light-emitting-diode (LED) backlight and patterned red–green–blue phosphor layers have been proposed. Improvements in luminous efficiency and lifetime have been systematically attempted. From the results of the accelerated aging test under near-UV irradiation under high temperature and humidity conditions, it has been confirmed that the e-LCD panel has a sufficiently long lifetime for practical use. The light conversion efficiency of the phosphor layer has been significantly improved by using optical filters. Commission Internationale de l'Eclairage (CIE) color coordinates are (0.69, 0.31) for red, (0.27, 0.68) for green and (0.15, 0.04) for blue sub-pixels. The corresponding color gamut is over 100% compared with that of the National Television System Committee. The e-LCD panel also has a considerable wide-viewing-angle property, and its overall luminous efficiency is more than twice higher than those of conventional LCD panels consisting of white-LED and color filters.
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.
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