Iwao Mitsuishi

Luminescence Properties of Eu2+-Doped Green-Emitting Sr-Sialon Phosphor and Its Application to White Light-Emitting Diodes

We developed a green-emitting phosphor Sr3Si13Al3O2N21:Eu2+ that is highly luminescent under excitation by blue light. It shows a highly efficient green luminescence whose external quantum efficiency reaches 67% for 460 nm excitation, and has small thermal quenching. Using this phosphor, we obtained white light-emitting diodes (LEDs) whose luminous efficacy and color rendering index Ra at 5330 K are 62 lm/W and 87, respectively. These features show that this green-emitting phosphor has high potential for application to white LEDs.

A revised Kubelka–Munk theory for spectral simulation of phosphor-based white light-emitting diodes

We developed a simulation method for designing the luminescence profiles of white light-emitting diodes (LEDs) with multicolor phosphor blend. By taking into account the effect of the light scattering by phosphor particles as well as the reabsorption effect by phosphor species, we found a model of white LEDs to calculate the light output as a function of various parameters such as the thickness of the resins, the concentration of phosphors, and the spatial distribution of phosphor particles. This method is widely applicable to phosphor-based white LEDs with either blue or UV excitation.

White Light-Emitting Diodes for Wide-Color-Gamut Backlight Using Green-Emitting Sr-Sialon Phosphor

We have successfully developed a white light-emitting diode (LED) for a wide-color-gamut backlight composed of a green-emitting phosphor Sr3Si13Al3O2N21:Eu2+ combined with a blue LED and a red-emitting phosphor CaAlSiN3:Eu2+. This white LED showed a discrete spectrum with distinct separation of red, green, and blue primary colors due to a narrow emission band of around 525 nm for the green phosphor. 94.2% of the wide color gamut of the National Television System Committee standard was attained by applying typical color filters of LCDs. The power LED module composed of 16 of these white LEDs revealed their excellent power dependence. The LED is expected to replace cold cathode fluorescent lamp (CCFL), and find a suitable application as a backlight in large-scale LCDs for in-vehicle use or for flat-panel television sets.

Numerical Simulation on Light Output of UV-based White Light-Emitting Diodes with Multicolor Phosphor Blends

We developed a new simulation method for designing the luminescence profiles of phophor-based white light-emitting diodes (LEDs). By combining the rate equations for absorption/emission processes by phosphors with a differential equation for spatial distribution of light intensity, we take into account the cascade process of phosphor emission due to the reabsorption of photons. We found that our model is suitable for a systematic design method of white light sources with multicolor phosphor blends.

Cation and anion ordering in Sr2Si7Al3ON13 phosphors

A series of photoluminescent Ce3+ doped samples with compositions close to Sr2Si7Al3ON13:Ce have been studied by neutron powder diffraction to determine the Si4+/Al3+ and N3−/O2− site ordering. Contrary to a commonly held assumption that the edge sharing tetrahedral sites in this structure are occupied exclusively by Al3+, we find a partial occupancy of Al3+ on these site but also an unexpected preference for Al3+ to occupy 2 other tetrahedral sites which are only corner sharing. From the crystal structures and local structures, as determined by pair distribution function (PDF) analysis, we also find evidence for alternating Si–Al site ordering within the edge sharing chains as well as dimerization of the Si4+ and Al3+ cations within these chains. The O2− are found to be partially ordered onto 2 of the anion sites, although small amounts of O2− are found on other sites as well. The cation and anion ordering found by neutron diffraction is supported by theoretical calculations. Understanding cation and anion ordering is essential for optimizing the photoluminescence properties of this promising class of phosphor materials.

30.3: Reduction of Electron‐Beam‐Induced Degradation of ZnS Green Phosphor Coated with Phosphate

Electron-beam-induced luminescence degradation is found to be reduced in ZnS: Cu, Al phosphor coated with a limited low content of phosphate. The behavior of the degradation is correlated with the quantities of SO2 and H2O gases released from the phosphors, analyzed by temperature programmed desorption-mass spectrometry (TPD-MS) and transmission electron microscopy (TEM) observations. We find that the layer coated with the appropriate phosphate content is uniform and continuous, which prevents the surface chemical reactions that cause the degradation.