Saturated green phosphors for LED applications (original) (raw)
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Thermal quenching and luminescence lifetime of saturated green Sr1−xEuxGa2S4 phosphors
Optical Materials, 2012
Due to the lack of efficient green emitting solid state light sources, conversion phosphors emitting saturated green emission are highly interesting, both for display and signalling applications. In this work, we study the luminescence properties of Sr 1Àx Eu x Ga 2 S 4 phosphors over a wide dopant concentration range (x = 0.01-0.3), as function of temperature. The phosphors show a saturated green emission over the entire studied range, with a typical peak wavelength around 536 nm and a FWHM of 50 nm. The internal quantum efficiency is 71% for x = 0.04. For this concentration, the emission intensity at 400 K is still 90% of the intensity at room temperature. By measuring both decay and thermal quenching profiles as a function of europium concentration, we were able to explain the emission properties on the basis of the local environment of the europium ions in the lattice.
Highly Luminescent (Zn0.6Sr0.3Mg0.1)2Ga2S5:Eu2+Green Phosphors for a White Light-Emitting Diode
Bulletin of the Korean Chemical Society
Green phosphors (Zn 1-a-b M a M' b) x Ga y S x+3y/2 :Eu 2+ (M, M' = alkali earth ions) with x = 2 and y = 2-5 were prepared, starting from ZnO, MgO, SrCO 3 , Ga 2 O 3 , Eu 2 O 3 , and S with a flux NH 4 F using a conventional solidstate reaction. A phosphor with the composition of (Zn 0.6 Sr 0.3 Mg 0.1) 2 Ga 2 S 5 :Eu 2+ produced the strongest luminescence at a 460-nm excitation. The observed XRD patterns indicated that the optimized phosphor consisted of two components: zinc thiogallate and zinc sulfide. The characteristic green luminescence of the ZnS:Eu 2+ component on excitation at 460 nm was attributed to the donor-acceptor () recombination in the hybrid boundary. The optimized green phosphor converted 17.9% of the absorbed blue light into luminescence. For the fabrication of light-emitting diode (LED), the optimized phosphor was coated with MgO using magnesium nitrate to overcome their weakness against moisture. The MgO-coated green phosphor was fabricated with a blue GaN LED, and the chromaticity index of the phosphor-cast LED (pc-LED) was investigated as a function of the wt % of the optimized phosphor. White LEDs were fabricated by pasting the optimized green (G) and the red (R) phosphors, and the commercial yellow (Y) phosphor on the blue chips. The three-band pc-WLED resulted in improved color rendering index (CRI) and corrected color temperature (CCT), compared with those of the two-band pc-WLED.
Green SrSi2O2N2:Eu2+ phosphor for LED-phosphor applications: synthesis and characterization
Bulletin of Electrical Engineering and Informatics, 2023
Green phosphors SrSi2O2N2:Eu2+ (SSON:Eu) are combined utilizing a simple solid-state reaction with SrSi2O2N2:Eu2+ like the forerunner. Various phosphor attributes were assessed following creation procedure. Differential thermal analysis (DTA) spectra and luminescence measurements are used to assess crystalline active power, electron-phonon conjunction, and heat quenching behavior. Because of their poor electron-phonon conjunction intensity (Huang-Rhys factor=4.2), SSON:Eu green phosphors have outstanding heating and color consistency. The heat quenching temperature (T50) of SSON:Eu is greater than 200 °C. SSON:Eu green phosphors have a wide stimulation range, strong heat steadiness and can absorb ultraviolet (UV) to blue energy and release green illumination, leading to the appropriate utilization in solid-state illumination and GaAsAl solar cells, according to the findings.
Application of (Ca1-xSrx)LaGa3S6O:Eu 2+ phosphor in white light-emitting diode fabrication
Indonesian Journal of Electrical Engineering and Computer Science, 2022
An alternating sequence of Ca1-xSrxLaGa3S6O:0.05Eu 2+ phosphors was produced using high-thermal and solid-state reactions. It has outstanding excitations at the range between 350 and 500 nm suitable for the closeultraviolet or GaN-based blue light-emitting diode light emitting diode (LED) chips. These phosphor peaks have a blue shift between 560 and 540 nm when the Sr concentration (x) rises. The Sr content (x) can be modified to produce an illumination with a color between yellow and green. As a result, we can conclude that solid solutions Ca1-xSrxLaGa3S6O:0.05Eu 2+ are excellent for use in manufacturing white LEDs. Our data may become valuable for producers in the task of making white light emitting diode (WLED) devices suitable for them.
Synthesis and optical properties of red/blue-emitting Sr2MgSi2O7:Eu3+/Eu2+ phosphors for white LED
Journal of Science: Advanced Materials and Devices, 2016
Phosphor-converted white light emitting diodes (white LEDs) have received great attention in recent years since they have several excellent features such as high lumen output, low power consumption, long lifetime and environmentally friendly. In this work, we report the co-precipitation synthesis of red/blue Sr 2 MgSi 2 O 7 :Eu 3þ /Eu 2þ phosphors with various Eu doping concentration. The results show that the obtained Sr 2 MgSi 2 O 7 :Eu 3þ /Eu 2þ phosphors have good crystallinity and emit strong red (Sr 2 MgSi 2 O 7 :Eu 3þ) and blue (Sr 2 MgSi 2 O 7 :Eu 2þ) emissions under near UV light excitation. The sharp emission peaks at 577, 590, 612, 653, and 701 nm corresponded to the typical 5 D 0 / 7 F j (j ¼ 0,1,2,3,4) transitions of Eu 3þ , and the blue emission peaking at 460 nm is attributed to the typical 4f 6 5d 1-4f 7 transition of Eu 2þ in the same Sr 2 MgSi 2 O 7 host lattice. Both phosphors can be well excited in the wavelength range of 260e400 nm where the near UV-LED is well matched. The above results suggest that the Sr 2 MgSi 2 O 7 :Eu 3þ /Eu 2þ phosphors are promising red/blue-emitting phosphors for the application in near UV pumped phosphorconverted white LEDs.
Application of (Ca1-xSrx)LaGa3S6O:Eu2+ phosphor in white light-emitting fabrication
Indonesian Journal of Electrical Engineering and Computer Science
An alternating sequence of Ca1-xSrxLaGa3S6O:0.05Eu2+ phosphors was produced using high-thermal and solid-state reactions. It has outstanding excitations at the range between 350 and 500 nm suitable for the close-ultraviolet or GaN-based blue LED chips. These phosphor peaks have a blue shift between 560 and 540 nm when the Sr concentration (x) rises. The Sr content (x) can be modified to produce an illumination with a color between yellow and green. As a result, we can conclude that solid solutions Ca1-xSrxLaGa3S6O:0.05Eu2+ are excellent for use in manufacturing white LEDs. Our data may become valuable for producers in the task of making white light emitting diode (WLED) devices suitable for them.
The commercially available white-light-emitting diodes (WLEDs) are made with a combination of blue LEDs and yellow phosphors. These types of WLEDs lack certain properties which make them meagerly applicable for general illumination and flat panel displays. The solution for such problem is to use near-ultraviolet (NUV) chips as an excitation source because of their high excitation efficiency and good spectral distribution. Therefore, there is an active search for new phosphor materials which can be effectively excited within the NUV wavelength range (350–420 nm). In this work, novel rare-earth free self-luminescent Ca 2 KZn 2 (VO 4) 3 phosphors were synthesized by a citrate assisted sol-gel method at low calcination temperatures. Optical properties, internal quantum efficiency and thermal stability as well as morphology and crystal structure of Ca 2 KZn 2 (VO 4) 3 phosphors for their application to NUV-based WLEDs were studied. The crystal structure and phase formation were confirmed with XRD patterns and Rietveld refinement. The optical properties of these phosphor materials which can change the NUV excitation into visible yellow-green emissions were studied. The synthesized phosphors were then coated onto the surface of a NUV chip along with a blue phosphor (LiCaPO 4 :Eu 2+) to get brighter WLEDs with a color rendering index of 94.8 and a correlated color temperature of 8549 K. A light-emitting diode (LED) is in the limelight since its invention by Nick Holonyak Jr. of General Electric Company and its application in solid-state lighting industry has gained a prominent interest. In the contemporary situation, white LEDs (WLEDs) have drawn great attention due to their wide range of applications and salient features like high efficiency, compact size, eco-friendly feature, high thermal stability and long operational lifetime 1,2. The commercially available WLEDs are prepared by coating a yellow-emitting Y 3 Al 5 O 12 : Ce 3+ (YAG: Ce 3+) phosphor on blue-emitting GaN LEDs 3,4. Such WLEDs have several drawbacks including poor color repro-ducibility, low color-rendering index (CRI) value and less thermal stability at high temperature. For the sake of its usage in general display applications, there is a need of high CRI and appropriate correlated color temperature (CCT). Therefore, the WLEDs visualized with near-ultraviolet (NUV) LED chips have been turned into a topic of research interest because their excitation efficiency is almost similar to that of fluorescent light bulbs and less than that of blue LED chips 5,6. For blue LED chips, the electroluminescence (EL) intensity considerably increases in the long wavelength band and saturates at high driving current, and the CCT value readily changes. There is also a non-uniformity in the spectral distribution due to low CRI values. On the other hand, NUV LED chips cannot be used to make YAG-based WLEDs due to weak light absorption in the NUV or deep blue spectral region. To overcome this, the search for a novel phosphor which can be excited in the wavelength range of 350–420 nm is building up. Broadly speaking, rare-earth materials are widely used in preparing host materials and as luminescent centers in many phosphors to generate multi-color lights 7–9. There are several reports found on rare-earth doped single host materials for WLEDs 10–15. Since all the rare-earth materials have similar chemical properties, they require high-cost separation, refinement and purification techniques which make them mostly expensive 16. Due to this, the design of rare-earth free materials is majorly needed. The rare-earth free phosphors can be understood with three main strategies: (i) use of transition metals for luminescent centers 17–22 , (ii) use of defects such as oxygen vacancies 23–26 and (iii) use of materials such as tungstates and vanadates 27–30 .
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
Selecting Conversion Phosphors for White Light-Emitting Diodes
Journal of The Electrochemical Society, 2011
Light emitting diodes (LEDs) are on the verge of a breakthrough in general lighting, due to their rapidly improving efficiency. Currently, white LEDs with high color rendering are mainly based on wavelength conversion by one or more phosphor materials. This Review first describes how to quantify the quality of a light source, discussing the color rendering index (CRI) and alternative color quality indices. Then, six main criteria are identified and discussed, which should be fulfilled by a phosphor candidate to be considered for actual application in LEDs. These criteria deal with the shape and position of the emission and the excitation spectra, the thermal quenching behavior, the quantum efficiency, the chemical and thermal stability and finally with the occurrence of saturation effects. Based on these criteria, the most common dopant ions (broad-band emitting Eu 2+ , Ce 3+ and Mn 2+ , lineemitting rare earth ions,...) and host compounds (garnets, sulfides, (oxy)nitrides,...) are
TELKOMNIKA Telecommunication Computing Electronics and Control, 2020
This study proposed the TRP, a remote phosphor structure that has 3 phosphor layers, to ehance the chromatic quality and lumen output for white light-emitting diodes devices (WLEDs). The arrangment of phosphor layers is yellow YAG:Ce 3+ phosphor, green Na3Ce(PO4)2:Tb 3+ phosphor, and red Na(Mg2-xMnX)LiSi4O10F2:Mn phosphor from bottom to top. Red Na(Mg2-xMnX)LiSi4O10F2:Mn phosphor is used for the red light component to boost color rendering index (CRI). The green layer Na3Ce(PO4)2:Tb 3+ phosphor is utilized for the green light component to produce higher luminous flux (LF). With the addition of red and green phosphor, the yellow YAG:Ce 3+ concentration must decrease to maintain the 6000 K color temperature. The research results show that red phosphor Na(Mg2-xMnX)LiSi4O10F2:Mn concentration is beneficial for CRI, while green phosphor Na3Ce(PO4)2:Tb 3+ is detrimental to CRI. Morever, CQS reaction with red and green phosphor is also studied, which show notable improvement when Na(Mg2-xMnX)LiSi4O10F2:Mn concentration is from 10-14%, regardless of Na3Ce(PO4)2:Tb 3+. The luminous flux (LF) can also increase for more than 40% with the reduced light loss and added green phosphor. Research results are valuable references for producers to enhance the color quality and the light emission of WLEDs. Keywords: Color quality scale Luminous flux Na(Mg2-xMnX)LiSi4O10F2:Mn Na3Ce(PO4)2:Tb 3+ Remote phosphor structure This is an open access article under the CC BY-SA license.