Selecting Conversion Phosphors for White Light-Emitting Diodes (original) (raw)
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Development of phosphors with high thermal stability and efficiency for phosphor-converted LEDs
2014
This article briefly reviews the developments of the phosphors with high thermal stability and high efficiency for use in phosphor-converted LED (pcLED) packages by Lightscape Materials Inc. (wholly owned by The Dow Chemical Company). The current industry design objectives for pcLED packages are first outlined with emphasis on the emission spectral features required for target brightness and color characteristics for general illumination and back light unit for liquid crystal displays. There is a growing demand on thermal stability of the phosphor emission as the LED package power increases. A phenomenological analysis is described on luminescence loss and its relation to thermal stability of luminescence emission at elevated temperatures, which serves as an empirical guide in the search for new phosphor materials of high thermal stability. Finally, the formulations and luminescence properties of the proprietary carbidonitride and oxycarbidonitride phosphors are discussed.
A novel phosphor structure for improving the luminous flux of white LEDs
Bulletin of Electrical Engineering and Informatics, 2022
This section focuses on the color uniformity and luminous production of multi-chip white-emitted LED lighting systems (MCW-LEDs) in improving illuminated performance. To accomplish the desired outcome, CaO:Sb 3+ must be mixed with their phosphor compounding, which has been shown to have a massive impact on illuminating effectiveness. There is also evidence that the increasing of yellowish-green-emitted phosphorus CaO:Sb 3+ concentration supports color homogeneity as well as luminescent effectiveness enhancements in MCW-LEDs featuring a 8500 K correlating colour temperature (CCT). Meanwhile, that rise in CaO:Sb 3+ concentration leads to the gradually deteriorating color quality scale. Thus, if appropriate concentration and particle size of CaO:Sb 3+ phosphor are determined, it is not hard to obtain such an excellent presentation in color uniformity, color quality scale and luminescence of MCW-LEDs.
Dy 3+-doped CaAl 12 O 19 phosphors were synthesized utilizing a combustion method. Crystal structure and morphological examinations were performed respectively using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques to identify the phase and morphology of the synthesized samples. Fourier transform infrared spectroscopy (FTIR) estimations were carried out using the KBr method. Photoluminescence properties (excitation and emission) were recorded at room temperature. CaAl 12 O 19 :Dy 3+ phosphor showed two emission peaks respectively under a 350-nm excitation wavelength, centered at 477 nm and 573 nm. Dipole-dipole interaction via nonradiative energy shifting has been considered as the major cause of concentration quenching when Dy 3+ concentration was more than 3 mol%. The CIE chromaticity coordinates positioned at (0.3185, 0.3580) for the CaAl 12 O 19 :0.03Dy 3+ phosphor had a correlated color temperature (CCT) of 6057 K, which is situated in the cool white area. Existing results point out that the CaAl 12 O 19 :0.03Dy 3+ phosphor could be a favorable candidate for use in white light-emitting diodes (WLEDs). KEYWORDS aluminate, concentration quenching, Dy 3 + , photoluminescence, WLEDs 1 | INTRODUCTION At the present time, the development of energy-saving lighting is an essential core interest for researchers. Large amounts of power can be saved by using efficient energy-saving light sources. Traditional incandescent and fluorescent lamps, with their resulting heat or gas release, have related colossal energy losses. [1] The use of energy proficient solid-state lighting appliances, for example compact fluorescent lamps (CFLs) and light-emitting diodes (LEDs), to deliver white light is an attractive alternative. Due to the above concern, the production of phosphors with excellent properties is an essential prerequisite. The efficacy of white light-emitting diodes (WLEDs) has surpassed that of incandescent lamps and fluorescent lamps. Due to their exceptional luminescence features, improved stability, energy-efficient nature, prominent luminescence efficiency, ecological amicability, and low cost, research into WLEDs has become more important. [2-4] WLEDs are mostly fabricated by applying three different techniques: (i) by making use of a mixture of red-green-blue (RGB) LEDs; (ii) through the utilization of ultraviolet (UV) LEDs to excite RGB phos-phors; and (iii) by employing blue LEDs to pump single-phase yellow or blended green and red phosphors. [1,5] At the present time, blue emitting chips combined with yellow phosphors (YAG:Ce 3+) are acknowledged as existing industrial WLEDs. Nevertheless, inferable from red light effect insufficiency, low color rendering index and high correlated color temperature (CCT) are commonly experienced by phosphors in this group. High CCT and low color rendering index (CRI) are not good factors when providing domiciliary or office lighting. This hindrance can be resolved by utilizing tricolor WLEDs dependent on red, green, and blue phosphors [6-8]. This purpose can be achieved by spreading these three phosphors on a transpicuous silicone that is then enclosed and then combined with blue or UV chips to excite the phosphors [1]. This factor is a major obstacle in field of materials science for the
Development of Blue Phosphor for White Light Emitting Diode
A simple procedure to prepare Eu 2+ activated CaI 2 phosphors is described. Photoluminescence (PL) results showed that the phosphor can be efficiently excited by UV-visible light from 250 to 425 nm, and exhibited bright blue emission around 462 nm. The effects of the doped -Eu 2+ concentration in CaI 2 :Eu 2+ on the PL were investigated in detail. The results showed that the relative PL intensity increases with Eu 2+ concentration increasing until a maximum intensity is reached, and then it decreases due to concentration quenching. Upon excited with 365 nm light, the present synthesized phosphor has higher emission intensity than that from the commercial blue phosphor, BaMgAl 10 O 17 :Eu 2+ . Bright blue lightemitting diodes can fabricate by the combination of the synthesized CaI 2 :Eu 2+ with 365 nm emitting GaNbased chips.
Study of photophosphors for white LEDs
Journal of Optical Technology, 2011
A comparative study has been carried out of the composition and the reflection and luminescence spectra of yttrium aluminum garnet and sialons as promising photophosphors. It is shown that the phase composition and surface inhomogeneity of the sialon particles has no effect on the position of the dopant levels in the band gap of the matrix or the photoluminescence spectra. It is established that the quantum efficiency of photophosphors synthesized on a sialon base and doped with europium is comparable with that of the garnet phosphor Y 3 Al 5 O 12 :Ce, and this makes it possible to use them in producing LEDs with white luminescence. The strength of the crystalline structure of sialons is significantly higher, and therefore the brightness and luminescence color of the photophosphors shows little dependence on time and temperature.
Indonesian Journal of Electrical Engineering and Computer Science, 2022
In the scenario of solid-state lighting (SSL) gradually replacing old standard techniques; the pc-LEDs (or diodes based on conversion phosphor) becomes a common method for creating white illumination, based on SSL. As of now, both of the UV-LEDs and the blue LEDs have been still being considered for the task of creating white illumination through phosphor excitation as it hasn't been known which LED type is truly superior. It is common that when it comes to phosphor, people will overlook the performance in LED devices with a wavelength range of 365 nm to 470 nm. Our research demonstrates the information concerning extrinsic quantum efficacy in the InxGa1-xN LED devices with the mentioned range as well as combines the information and the effectiveness of phosphor for the task of examining the performance of near-UV and blue LEDs and creating white illumination. In addition, the research demonstrates recreations for the task of assessing the white illumination mixtures under the correlated color temperature of 3000 K and 4000 K in the two LED structures.
A comprehensive discussion on colour conversion element design of phosphor converted LEDs
Journal of Solid State Lighting, 2014
For a systematic approach to improve the white light quality of phosphor converted light-emitting diodes (LEDs) for general lighting applications it is imperative to get the individual sources of error for correlated colour temperature (CCT) reproducibility and maintenance under control. In this regard, it is of essential importance to understand how geometrical, optical and thermal properties of the colour conversion elements (CCEs), which typically consist of phosphor particles embedded in a transparent matrix material, affect the constancy of a desired CCT value. In this contribution we use an LED assembly consisting of an LED die mounted on a printed circuit board by chip-on-board technology and a CCE with a globe-top configuration on the top of it as a model system and discuss the impact of the CCE size, the substrate reflectivity as well as the thermal load of the CCEs on CCT maintenance and the respective radiant fluxes. It turns out that optimized solutions for CCT maintenan...
Essential Factor for Determining Optical Output of Phosphor-Converted LEDs
IEEE Photonics Journal, 2014
An essential factor of the particle number is exploited for the phosphor excitation in phosphor-converted white LEDs. The particle number can clearly reveal the dependence of the light output flux and the correlated color temperature upon the conventional parameters, thickness, and concentration of the phosphors in a simpler way. In addition, we also find that there might exist an optimal particle number for the maximal luminous light output. An empirical function is then proposed for successfully modeling the relation between the output light and the particle number.
New phosphors for white LEDs: material design concepts
Efficient phosphors for white LEDs have been successfully developed, wherein some Material Design Concepts were utilized to promote our research and development effectively and efficiently. Useful ideas for the development of our red and green phosphors, Sr-rich (Sr, are reviewed.