Luminescence and electron paramagnetic resonance investigation on ultraviolet emitting Gd doped MgAl2O4 phosphors

There are several methods to produce a white light emitting diode (LED). The most common commercially available white LED is made by mixing the blue light from a GaN chip and the yellow light from the emission of a yttrium aluminum garnet cerium (YAG:Ce) yellow phosphor coating. The quality of white LED using this approach heavily depends on the optimization of packing density, thickness and uniformity of the phosphor layer. The present study is intended to develop a new methodology for coating a uniform yellow phosphor layer. This newly developed coating method is based on the concept of screen-printing. A matrix array of LEDs is firstly mounted on a silicon substrate with the flip chip configuration. A silicon mold plate is fabricated with etched cavities that match with the dimensions and pattern of LED array. The silicon mold plate is then placed over the substrate that carries the LED array and serves as a printing mask. The yellow phosphor powder is pushed into the apertures by a squeegee blade and bonded to the LED with UV curable epoxy. The silicon mold plate is released after curing. Compared with other coating approaches, this yellow phosphor printing method is relatively simple and can make good quality white LEDs

Process development for yellow phosphor coating on blue light emitting diodes (LEDs) for white light illumination

Radioluminescence (RL) and thermoluminescence (TL) in spinel crystals and ceramics were investigated to elucidate the radiation-induced electronic processes in single crystals grown by Verneuil and Czochralski methods as well as transparent and translucent ceramics. Both RL and TL spectra demonstrate a UV-band related to electron–hole recombination luminescence at intrinsic defects; green and red luminescence are identified with emission of Mn 2+ - and Cr 3+ -ions, respectively. The kinetics of growth of different RL luminescence bands depending on dose at the prolonged X-irradiation shows the competitive character of charge and energy transfer between defects and impurity ions. The dependence of RL intensity on the temperature of the sample was measured in the range of 300–750 K and compared with TL for different emission bands. The variety of maxima in the temperature dependence of RL and in the glow curves of TL measured for different luminescence bands in spinels of different origins and crystalline forms is used to show that charge carrier traps and luminescence centers are not isolated defects but are complexes of defects and impurities. The formation, structure and properties of these complexes depend on the processing conditions.

Radiation-induced luminescence in magnesium aluminate spinel crystals and ceramics

Structural characterizations and waveguiding properties of YAG thin films obtained by different sol gel processes

A light emitting element is provided, including a first electrode layer, a second electrode layer, and an organic light emitting layer sandwiched between the first electrode layer and the second electrode layer. The organic light emitting layer is patterned to include a plurality of light emitting blocks with different densities. In an embodiment, the light emitting blocks are divided into a plurality of light emitting block groups that are arranged in an alternate manner. In another embodiment, a light emitting element includes a first electrode layer, a first organic light emitting layer, a charge generating layer, a second organic light emitting layer, and a second electrode layer sequentially stacked on one another. The first and second organic light emitting layer are patterned to form a plurality of first and second light emitting blocks with different densities, respectively. Thus, the light emitting element generates full-color, gray-scale, three-dimensional, or dynamic images.

Light emitting element

A new kind of YAG (yttrium aluminum garnet) phosphor screen for projection cathode ray tubes is reported. The 3 in YAG phosphor screen is fabricated by depositing phosphor powder on a YAG faceplate. Owing to the YAG characteristic of higher heat conductivity than the conventional glass faceplate, the YAG phosphor screen obtains very high brightness, good contrast ratio and high resolution, and hence realises large-screen projection displays.

YAG phosphor screen for projection CRT

The crosstalk, equivalent circuit, voltage drop and power consumption of passive matrix organic light-emitting diodes (PMOLEDs) are quantitatively analyzed, and a mathematical model to calculate the power of PMOLEDs is built. In particular, the advantages of dual-panel PMOLEDs are discussed. The model demonstrates that the power of dual-panel PMOLEDs can be significantly reduced comparing with that of single-panel PMOLEDs. Two 2.5-in. 128 × 64-pixel green small molecule PMOLEDs have been fabricated. One is single-panel, and the other dual-panel. The power consumption of dual-panel PMOLEDs is 25% less than that of single-panel when both are operated at an average luminance of 100cd/m 2 . Key words: organic light-emitting diodes; passive matrix; dual-panel; power consumption 1. Introduction Many researchers are interested in organic light-emitting diodes (OLEDs) since C. W. Tang et al. [1] demonstrated a double layer structure in 1987. Because OLEDs have many advantages, such as high brightness, large viewing angle, fast response time, ultra-thin structure, light weight, low driving voltage and low power consumption [2][3], they are praised as the third generation display device substitute for CRT and LCD. There are two kinds of addressing technology for OLEDs, PMOLEDs and active matrix OLEDs (AMOLEDs). PMOLEDs have a simpler structure to fabricate, and their cost is lower than AMOLEDs. So small size and low content display devices commonly use PMOLEDs. Usually crosstalk is evident in flat-panel display, especially for LCDs. Crosstalk of PMOLEDs has been discussed in quantity [4][5][6], but limited in non-operated condition. To apply PMOLEDs to the field of PDA and mobile communication, a low power consumption device that uses a battery as power supply is demanded. So we need to know the driving voltage, driving current and power consumption of OLEDs. The voltage drop in the electrode of PMOLEDs has been calculated [4], however, the discussion didnt fully consider all the working conditions. The power consumption of PMOLEDs was divided into three kinds [7], but the entire calculated process was not given. In this paper, the crosstalk, voltage drop on the electrode and power consumption of PMOLEDS will be discussed in detail. In order to understand the crosstalk of PMOLEDs, the simple equivalent and exact equivalent circuit of 5*5 PMOLEDs are given in Section 2. In the case of PMOLEDs is addressed line by line, the voltage drop on the electrode is different compared to PMOLEDs addressed by static technology. The range of the voltage drop is discussed in section 3, when PMOLEDs is addressed line by line. Section 4 presents a mathematical model to calculate the power consumption of PMOLEDs. In addition, dual-panel PMOLEDs technology to reduce the power is proposed, and the calculated results of dual-panel and single-panel PMOLEDs are compared. In section 5, both dual-panel and single-panel PMOLEDs are fabricated, measurement data of power consumption conform the calculation in section 4.

Design of passive matrix organic light-emitting diodes

A type of optical constants measuring system controlled by a computer was developed. The system consists of a focusing lens, a monochromator that is composed of a diffraction grating and a photomultiplier, a high-precision voltage amplifier, a level buffer circuit, a data-sampling card composed of a A/D converting circuits, a interrupt circuit and I/O interface circuits and a PC. The heart of the system is a PC, which is served as data sampling, processing and calculating unit. The transmission spectrum of α:H silicon film is measured by this system. Then, a kind of envelopes calculation method proposed by Manifacier is used to calculate refractive index, absorptive coefficient and optical band. The accuracy is of the same orders as for the iteration method.

Optical constants measurement system for α:H silicon film

We have developed 5-in. projection CRTs using multi-crystal material MgAl2O4 as the phosphor screen substrate. An experimental 50-in. rear-projection TV incorporating the projection tubes achieved more than 1600 TV lines of horizontal resolution and 1800 lumens of brightness.

36.4: A 5-in. CRT for High Luminance and High Resolution Projection Display

— We have developed a 3-in. YAG (yttrium aluminum garnet) projection CRT for an HDTV display. The densely packed phosphor screen with a multi-layer interference filter is prepared by depositing phosphor on a YAG faceplate using a centrifugal sedimentation method. The tube's envelope is made from a glass whose expansion coefficient is well-matched with that of YAG. The focusing characteristics of an optimally designed pre-focusing electron gun and focusing magnet are improved for a HDTV display application. As a result, the green, red, and blue tubes reached luminances of 1.4 × 105, 6.2 × 104, and 8 × 103 cd/m2 at a cathode current of 1.0 mA and an anode voltage of 29 kV, respectively, with a half-intensity linewidth of 85 μm. An experimental 48-in. rear-projection TV set using the YAG projection tubes achieves more than 1000-TV-lines horizontal resolution and 300-cd/m2 mean white luminance.

Zulun Lin

Papers

YAG phosphor screen for projection CRT

Design of passive matrix organic light-emitting diodes

Optical constants measurement system for α:H silicon film

36.4: A 5-in. CRT for High Luminance and High Resolution Projection Display

A high-luminance and high-resolution CRT for projection HDTV display