A review on the advancements in phosphor-converted light emitting diodes (pc-LEDs): Phosphor synthesis, device fabrication and characterization

doi:10.1016/j.pmatsci.2019.100622

Progress in Materials Science

Volume 109, April 2020, 100622

https://doi.org/10.1016/j.pmatsci.2019.100622 Get rights and content

Abstract

This article puts emphasis on the role of phosphors in the advancement of Light-emitting diodes (LEDs). The increasing use of phosphors in LEDs, consequently, led to the nomenclature of phosphor-converted LEDs (pc-LEDs). This article makes a thorough discussion about the various methods employed for the synthesis of phosphors and the materials involved in the fabrication of pc-LEDs. A review on the various color-emitting phosphors has been exclusively made to understand the combinations of host materials with luminescent ion dopants that are essential to produce a specific color-emission of interest. There is a brief outlook on the various characteristics and indexes associated with the color quality and performance of pc-LEDs. The challenges faced by pc-LEDs and the advances made to overcome them have also been discussed. On the parallel, other variants of LEDs have started to show up with more promising features than pc-LEDs; but those are yet to accomplish a place in the LED industry due to the lackluster observed in their stability and lifetime. This article will brief the records on such new variants of LEDs assuming that these issues will be resolved in the near future and establish them as the next-generation of LEDs.

Introduction

In this modern era of digitization, the deficiency of energy is more often felt when the electrical power generated on this planet is inefficiently consumed for lighting applications [1]. Catastrophic circumstances are in clear view if energy is not utilized judiciously and wisely for lighting. The ever-rising demand for energy may cause a host of changes on the environment and this need to be advocated before time lapses out. The root to this problem may be the inefficiency displayed by devices that consume high amount of energy for a low output yield. When it comes to lighting, the key holds in proper selection of high efficiency phosphors capable of giving good visible light emission. Apart from energy efficiency, it is equally important to ensure the environment friendly nature of the lighting technology. If all these conditions are to be satisfied, there is no other better choice than the solid state lighting. Solid state lighting is based on the light emitting diodes that are basically p-n junction semiconductor chips forward biased to emit light. Their emission wavelength immensely depends on the composition of the semiconductor chip and the forward bias voltage. GaN [2], [3], InGaN [4], [5], AlGaN [6], [7], AlInGaP [8] were some of the LED chips that have been used to produce different wavelengths of emission. However, there is a limit to the wavelength range covered by such semiconductor chips. With an aim to conquer the pitfalls accompanied by these LED chips and to provide a better spectrum of light emission, downconverting phosphors and quantum dots were introduced into play.

Phosphor-converted light emitting diodes (pc-LEDs) have marvelous advantages over other conventional sources of lighting, especially in terms of the luminous efficiency, low power consumption, durability, eco-friendliness and long operational life time [9], [10]. pc-LEDs employ phosphors coated on the LED chip or on the walls of the encapsulant that can be excited by the UV or blue light emitted from the chip. Inorganic phosphors doped with lanthanide ions are the mainstream essence of pc-LEDs. Lanthanide elements have a typical characteristic to get excited by absorbing UV or near-UV light and then bring out the emission in the form of visible light. Lanthanides are part of the f-block series of elements and are more commonly known as rare earths. Although actinides also come under this series, they are neatly ignored from being a part of pc-LEDs. Citing the radioactive nature of these elements, actinides are never preferred in phosphors. Except for La and Lu, all of the elements in the lanthanide series are capable of exhibiting luminescence. The lanthanide elements are capable of showing their emissions in their +3 oxidation state. Eu has an additional feature of exhibiting luminescence in both +2 and +3 oxidation states [11], [12], [13], [14], [15], [16], [17], [18]. Apart from lanthanides, there are some transition metals that also proved to be potential dopants for luminescence. These include mainly Cu, Mn, Cr with oxidation states +1, +2, +3, +4. The dopants act as activators in an inert host matrix, which may be either an oxide, nitride, phosphate, fluoride, borate, sulfate, aluminate, silicate, sulfide, tungstate, vanadate, molybdate, etc. A host matrix with a band gap between 3 and 5 eV is considered to be the best for a phosphor. Most of the host lattices are inactive and do not luminesce directly in the absence of a luminescent ions. That’s why they require a luminescent ion (or activator) to activate the luminescence phenomenon in such hosts. In some cases, even the activator fails to efficiently absorb the energy and convert it into luminescence emission. Here, a supporting role is played by a sensitizer ion that efficiently absorbs energy and transfer a part or whole of it to the activator, thereby, giving a significant improvement in their luminescence emission. Some hosts like vanadates or tungstates are themselves capable of getting excited by UV light and radiate emission in the near-UV or visible region [19], [20], [21], [22], [23], [24]. Such hosts are known as host luminophores [25]. But the main criterion for a phosphor to be utilized in a pc-LED is that they must show a strong absorption in the UV or near-UV region and must have an efficient emission in the visible light region. Also, it is important that the transitions responsible for the excitation and emission must not be forbidden. In the present review, we summarize the methods involved in the synthesis of LED phosphors and their fabrication in a pc-LED. There is also a passing note on the different characteristics of phosphors incorporated in pc-LEDs.

Section snippets

Synthesis of phosphors

An efficient research on phosphors requires an exceptionally clean chemical laboratory to synthesize very pure substances, furnaces capable of attaining temperatures greater than 1600 °C and a good physics laboratory for the analysis and characterization of the synthesized materials [26]. The degree of purity of materials is generally categorized as ore (1% pure), technically pure (90% pure), chemically pure (99.9% pure), reagent-grade pure (99.99% pure), spectroscopically pure (99.999% pure),

Effect of synthesis routes on the morphology of phosphors

An appropriate choice of synthesis route can lead to exceptional morphologies of phosphors with enhanced luminescence properties. Several wet chemical methods are known for their ability to design the particles into some brilliant forms. By making some alterations in the traditional methods, it is also possible to control the particle size and shape as well as their growth during the synthesis.

The quest for nanophosphors has gained immense popularity in the recent years due to their enhanced

Role of transition metal (TM) ions in LED phosphors

The activator ions doped into a solid host lattice experience a local crystalline environment that has immense influence on the luminescence properties of that activator ion. The activator ion in the crystalline host acts as a luminescence center. This activator ion may be a transition metal ion or a rare-earth ion. They are generally coordinated by ligands in a host lattice. The attraction between the positively charged activator ion and the negatively charged non-bonding electrons of the

Role of lanthanide ions in LED phosphors

Lanthanides form the most significant class of luminescent dopants that are introduced in inorganic solids for LEDs. There are fifteen elements under the lanthanide series that extend from lanthanum (La) to lutetium (Lu). The elements in the extreme ends of the series are La and Lu, which possess completely empty and completely filled 4f orbitals, respectively. As a result, they do not possess electronic levels to initiate any f-f or f-d transitions capable of producing luminescence. In

Red-emitting phosphors

Eu³⁺ doped phosphors are the most sought red emitting phosphors due to their deep red emissions from 593 to 650 nm [115]. A perfect red component with pure color purity is obtained by the ⁵D₀ → ⁷F₂ transition of Eu³⁺, corresponding to the emission wavelength ~615 nm [116], [117], [118]. There is a general belief that Eu³⁺ ions will show their characteristic emission even if they are doped in mere sand. But not all the Eu³⁺ doped phosphors are suitable for lighting purpose. While considering

Color-tunable phosphors

In order to meet the requirements of modern lighting technology, efforts are being made to acquire phosphors capable of spectral tuning that could probably improve the luminous efficiency, color rendering index and color gamut of pc-LEDs. The changing light generations will witness a huge revolution in the lighting industry that shall be brought about by these color tunable phosphors. Li et al. have elaborately discussed, in their review, several strategies that may be employed to successfully

Characteristics of LED phosphors and the quality of light

The quality and the quantity of the output derived from a source of light determine the validity of the research on that particular light source. While considering any source of light for illumination purpose, it is crucial to understand the way it is perceived by human eye. A number of quantitative metrics have been developed to characterize and optimize the lighting systems with regard to perceived quality. The CIE (Commission Internationale de I’Eclairage) is currently the only

Challenges in pc-LEDs

A matter of concern over the chemical and thermal stability of phosphors often ascends whenever it is considered for LED applications. It is highly recommended that a phosphor must be chemically stable even under moist conditions. Lin et al. discussed the possibility of using flux materials along with the precursors during the synthesis of phosphor to enhance its chemical stability [339]. Flux materials are often used in synthetic methods involving high temperatures. These materials melt at

Newest trends in LEDs

LEDs are emerging towards bringing in a new revolution in the lighting industry. Already they have started replacing the traditional lamps in most parts of the world and are progressively becoming the prime source for both household and street lighting. The move to adapt the green technology has resulted in dumping of the hazardous mercury based lighting and this has paved way for the LED luminaires to spread their existence as the prime lighting system. The green technology has granted

Concluding remarks and outlook

The rapid advancement in LED technology has paved way to numerous innovations. Now, LEDs are not just limited to lighting needs. Their significant applications in countless sectors are gaining huge admiration. The changing requirements led to numerous modifications in the LED configuration and this has enabled LEDs to move steps ahead from the age-old semiconductor physics. One of the major concerns in primitive semiconductor LEDs was the difficulty to obtain a color wavelength other than the

Acknowledgement

This research is supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa (Grant 84415). The financial assistance from the University of the Free State is highly recognized.

One of the authors SJD is thankful to Department of Science and Technology (DST), India (Nano Mission) (Project Ref. No. DST/NM/NS/2018/38(G), dated 16/01/2019) for financial assistance and R.T.M.Nagpur University, Nagpur for

References (379)

J. Liu et al.
Study on luminescence and thermal stability of blue-emitting Sr 5 (PO 4) 3 F: Eu 2+ phosphor for application in InGaN-based LEDs
Mater Sci Eng B
(2017)
H. Yu et al.
Novel tunable red to yellow emitting (Ca, Ba)₄(PO₄)₂O:Eu²⁺ phosphor for blue-excited white light emitting diodes
Ceram Int
(2017)
N.V. Rebrova et al.
Crystal growth and characterization of Eu²⁺ doped RbCaX₃ (X = Cl, Br) scintillators
J Cryst Growth
(2017)
M. Dalal et al.
Crystal structure and Judd-Ofelt properties of a novel color tunable blue-white-red Ba₅Zn₄Y₈O₂₁:Eu³⁺ nanophosphor for near-ultraviolet based WLEDs
J Alloys Compd
(2017)
X. Sun et al.
Preparation and luminescence properties of Sr₂Eu_xLa_1−xAlO₅ phosphor
J Lumin
(2015)
B. Poornaprakash et al.
Achieving room temperature ferromagnetism in ZnS nanoparticles via Eu³⁺ doping
Mater Lett
(2016)
S. Tamboli et al.
Analysis of electron-vibrational interaction in the 5d states of Eu2⁺ ions in A₃P₄O₁₃ and A₃(PO₄)₂ (A=Sr, Ba) phosphors
J Lumin
(2017)
E. Cavalli et al.
Luminescence dynamics in CaWO₄:Pr³⁺ powders and single crystals
J Lumin
(2016)
H. Xu et al.
Surfactant-assistant solvothermal synthesis of CaWO₄:Eu³⁺ phosphors and luminescence
Superlatt Microstruct
(2015)
H. Zhu et al.
Photoluminescence properties of Li₂Mg₂(WO₄)₃:Eu³⁺ red phosphor with high color purity for white LEDs applications
J Lumin
(2016)

R. Cao et al.

Synthesis and luminescence properties of Sr₃(VO₄)₂:Eu³⁺ phosphor and emission enhancement by co-doping Li⁺ ion

Optik (Stuttg)

(2016)

L. Jing et al.

Synthesis and photoluminescence properties of Ca₉Y(VO₄)₇: Dy phosphors for white light-emitting diodes

J Lumin

(2015)

X. Mi et al.

Synthesis and luminescence of Ca₉Eu_1−xLn_x(VO₄)₇ (Ln=Y, La, Gd, Lu) phosphors

Mater Res Bull

(2014)

J. Ru et al.

Synthesis and luminescence characteristics of Li₂Y_4–xEu_x(WO₄)_7–y(MoO₄)_y red-emitting phosphor for white LED

J Rare Earths

(2013)

F. Chen et al.

Photoluminescence properties of Sr₃(PO₄)₂: Eu²⁺, Dy³⁺ double-emitting blue phosphor for white LEDs

Opt Mater

(2014)

B. Yan et al.

Photoluminescent properties of Dy³⁺-activated REAl₃(BO₃)₄ (RE=Y, La, Gd) polycrystalline phosphors from hybrid precursors

J Alloys Compd

(2008)

A. Durugkar et al.

Novel photoluminescence properties of Eu³⁺ doped chlorapatite phosphor synthesized via sol-gel method

Mater Res Bull

(2018)

X. Li et al.

Influence of pH value on properties of YPO₄:Tb³⁺ phosphor by co-precipitation method

J Rare Earths

(2015)

B.V. Rao et al.

Synthesis and photoluminescence characterization of RE³⁺ (=Eu³⁺, Dy³⁺)-activated Ca₃La(VO₄)₃ phosphors for white light-emitting diodes

J Alloys Compd

(2010)

J. Lian et al.

Co-precipitation synthesis of Y₂O₂SO₄:Eu³⁺ nanophosphor and comparison of photoluminescence properties with Y₂O₃:Eu³⁺ and Y₂O₂S :Eu³⁺ nanophosphors

Solid State Sci

(2015)

S.A. Pardhi et al.

Investigation of thermoluminescence and electron-vibrational interaction parameters in SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors

J Lumin

(2017)

T. Peng et al.

Combustion synthesis and photoluminescence of SrAl₂O₄:Eu,Dy phosphor nanoparticles

Mater Lett

(2004)

M. Upasani et al.

Synthesis, characterization and optical properties of Y₃Al₅O₁₂: Ce phosphor by mixed fuel combustion synthesis

J Alloys Compd

(2015)

J. Sun et al.

Combustion synthesis and luminescence properties of blue NaBaPO₄:Eu²⁺ phosphor

J Rare Earths

(2012)

C. He et al.

Microwave solid state synthesis and luminescence properties of green-emitting Gd₂O₂S:Tb³⁺ phosphor

Opt Mater (Amst)

(2015)

C.S. Lim et al.

Microwave sol–gel synthesis and upconversion photoluminescence properties of CaGd₂(WO₄)₄:Er³⁺/Yb³⁺ phosphors with incommensurately modulated structure

J Solid State Chem

(2015)

Q. Cheng et al.

Preparation and tunable luminescence of CaCO₃:Eu³⁺, T^b3+ phosphors

J Lumin

(2014)

J. Prado-Gonjal et al.

Increased ionic conductivity in microwave hydrothermally synthesized rare-earth doped ceria Ce_1−xRE_xO_2−(x/2)

J Power Sources

(2012)

J. Sun et al.

Improved moisture resistance of SrSO₄:Sm³⁺ phosphors coated with SiO2

Appl Surf Sci

(2012)

Y.N. Zhu et al.

Luminescent properties of Sr₄V₂O₉:Eu³⁺, B^a2+ phosphors prepared by a solvothermal method

Mater Res Bull

(2015)

N. Jia et al.

Property of YAG: Ce phosphors powder prepared by mixed solvothermal method

J Alloys Compd

(2011)

Y.H. Wang et al.

Hydrothermal synthesis and photoluminescence of novel green-emitting phosphor Y_1-xBO₃:xTb³⁺

Mater Res Bull

(2006)

J.I. Pankove et al.

Electroluminescence in GaN

J Lumin

(1971)

J.I. Pankove et al.

GaN blue light-emitting diodes

J Lumin

(1972)

H.P. Maruska et al.

Preparation of Mg-doped GaN diodes exhibiting violet electroluminescence

Mater Res Bull

(1972)

K.L. Suk et al.

Flexible Chip-on-Flex (COF) and embedded Chip-in-Flex (CIF) packages by applying wafer level package (WLP) technology using anisotropic conductive films (ACFs)

Microelectron Reliab

(2012)

L.-B. Chang et al.

Comparison of silicone and spin-on glass packaging materials for light-emitting diode encapsulation

Thin Solid Films

(2014)

Z. Gao et al.

Thermal chemical vapor deposition grown graphene heat spreader for thermal management of hot spots

Carbon N Y

(2013)

Z. Zhang et al.

A novel white emission in Ba₁₀F₂(PO₄)₆:Dy³⁺ single-phase full-color phosphor

Mater Chem Phys

(2015)

F. Xiao et al.

Warm white light from Y₄MgSi₃O₁₃:Bi³⁺, Eu³⁺ nanophosphor for white light-emitting diodes

Spectrochim Acta - Part A Mol Biomol Spectrosc

(2009)

F. Li et al.

Emission tunable CdZnS/ZnSe core/shell quantum dots for white light emitting diodes

J Lumin

(2017)

R. Cao et al.

Synthesis and luminescence properties of Li₂SnO₃:Mn⁴⁺ red-emitting phosphor for solid-state lighting

J Alloys Compd

(2017)

M.G. Brik et al.

On the optical properties of the Mn⁴⁺ ion in solids

J Lumin

(2013)

Y.D. Xu et al.

Preparation and luminescent properties of a new red phosphor (Sr₄Al₁₄O₂₅:Mn⁴⁺) for white LEDs

J Alloys Compd

(2013)

Z. Qiu et al.

Effectively enhancing blue excitation of red phosphor Mg₂TiO₄:Mn⁴⁺ by Bi³⁺ sensitization

J Lumin

(2015)

J. Zhang et al.

Investigation on luminescence of red-emitting Mg₃Ca₃(PO₄)₄:Ce³⁺, Mⁿ²+ phosphors

J Rare Earths

(2015)

J. Zhou et al.

The synthesis and photoluminescence of a single-phased white-emitting NaAlSiO₄:Ce³⁺, Mn²⁺ phosphor for WLEDs

Mater Res Bull

(2016)

R. Zhong et al.

Red photoluminescence due to energy transfer from Eu²⁺ to Cr³⁺ in BaAl₁₂O₁₉

J Lumin

(2010)

B. Malysa et al.

Temperature dependent Cr³⁺ photoluminescence in garnets of the type X₃Sc₂Ga₃O₁₂ (X = Lu, Y, Gd, La)

J Lumin

(2018)

J. McKittrick et al.

Review: Down conversion materials for solid-state lighting

J Am Ceram Soc

(2014)

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An activator’s selective occupation of a host is of great significance for designing high-quality white light-emitting diodes (w-LEDs) phosphors, while achieving a full-spectrum single-phase white light emission phosphor is challenging. For developing high-performance and green-emitting phosphors with narrow bands used for backlight display, a series of Na₂Mg_1-xAl₁₀O₁₇:xMn²⁺ (NMAO:xMn²⁺) phosphors with high Mn²⁺ concentration were synthesized. The NMAO:0.65Mn²⁺ green phosphor exhibits an ultra-narrow band green emission with full width at half maximum (FWHM) about 27 nm and peak position at 513 nm when excited by the blue light with wavelength of 450 nm. The NMAO:0.65Mn²⁺ not only has a super narrow band which is narrower than β-SiAlON:Eu²⁺ (FWHM ∼ 55 nm) but also shows an exceptional thermal stability performance (77% peak intensity @423 K). A w-LED device was assembled with NMAO:0.65Mn²⁺, a blue GaInN chip and K₂SiF₆:Mn⁴⁺ phosphors, which represents a wide color-gamut of 112% National Television System Committee (NTSC) standard under the current of 50 mA. These results demonstrate the NMAO:0.65Mn²⁺ has potential superiority in application of backlight display.
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Dr. Govind B. Nair is currently a Post-Doctoral researcher in the University of Free State, Bloemfontein, South Africa. He pursued his PhD from R.T.M. Nagpur University under the erudite guidance of Prof. S. J. Dhoble. He obtained his Masters degree in Physics from R.T.M. Nagpur University, Nagpur, India. He bagged two gold medals for securing first rank in his Masters degree. He was awarded with INSPIRE Fellowship, which is a prestigious fellowship programme conducted by the Department of Science and Technology (DST), India. He is credited with 30 research papers in SCOPUS-indexed journals with high repute. He was also awarded with the Summer Research Fellowship by the Indian Academy of Sciences (IASc) in 2012 to work on a project in Raja Ramana Centre for Advanced technology (RRCAT), Indore, India. His area of research includes the synthesis and characterization of Optical materials, theoretical analysis of luminescence processes, structural analysis of materials, etc.

Hendrik C. Swart is a B1 NRF rated researcher (Internationally acclaimed researchers) and currently a Senior Professor in the Department of Physics at the University of the Free State. Over the past 24 years he has led research in the area of the degradation of phosphors for field emission displays, as well as developing materials for nano solid state lighting. He has been key in the development of processes to synthesise and deposit thin films of various types of semiconductor nano-particles, which will enhance the colour, luminescent intensity and lifetime of such displays. He has more than 620 publications in international peer reviewed journals, 112 peer reviewed conference proceedings and editor/author or co-editor/author of 25 book chapters and or books with more than 10115 cited author references on google scholar and more than 540 national and international conference contributions (authored and co-authored). He has an ISI H-index of 37 (rid=g-2696-2012). He is a reviewer for about 100 international and national professional journals in his field (or in related fields), and a member of the editorial board of the high impact factor journal ‘Critical Reviews in Solid State and Materials Sciences” (IF-6.455). He is on the editorial board of Applied Surface Science (IF-5.155). He has received the South African National Science and Technology Forum (NSTF) award in 2009 for research capacity development of students in the niche area of nanophysics. His commitment to the next generation of scientists is also reflected by the awards he received from the Faculty of Natural and Agricultural Sciences at the University of the Free State, South Africa for excellence (deans medal) (2012), research (2014), mentorship (2008), for academic entrepreneurship (2009), best researcher (2018). The International Association of Advanced Materials (IAAM) honored him with the prestigious IAAM Scientist award for 2014 at the SETCOR International Conference on Smart Materials and Surfaces, Bangkok - Thailand. He received honorary membership of the Golden Key Association (2012). Radio Rosestad award for outstanding research and post graduate teaching in 2017. He was chair of national and international conferences. He has supervised 80 PhD and MSc students successfully in the past with another 22 in progress and has established a National Nano Surface Characterization Facility (NNSCF) containing state of the art surface characterization equipment. A research chair in Solid State Luminescent and Advanced Materials was awarded to him from the South African Research Chairs Initiative (SARChI) at the end of 2012 which was renewed for another 5 year at the end of 2017. The main focus of his research group will be the improvement of luminescent materials for applications in Flat Panel Displays and Solar Cells; the development of Organic light emitting diodes (OLED) materials as well as materials for power saving solid state lighting devices.

Dr. S.J. Dhoble obtained M.Sc. degree in Physics from Rani Durgavati University, Jabalpur, India in 1988. He obtained his Ph.D. degree in 1992 on Solid State Physics from Nagpur University, Nagpur. Dr. S.J. Dhoble is presently working as Professor in Department of Physics, R.T.M. Nagpur University, Nagpur, India. During his research career, he is involved in the synthesis and characterization of solid state lighting materials, EVI parameter as well as development of radiation dosimetry phosphors using thermoluminescence, mechanoluminescence and lyoluminescence techniques and utilization of fly ash. Dr. Dhoble published more than six hundred thirty four research papers in international and national reviewed journals and presented more than 1346 research papers in international and national conferences on solid-state lighting, LEDs, radiation dosimetry, phototherapy and laser materials. As per SCOPUS database, he holds the top position in the world in terms of publications on phosphor materials, LED, radiation dosimetry materials. He is elected as the Fellow of Luminescence Society of India. He recently received Career-360 Best Faculty Research Awards-2018, Best Research Award-2016, R.T.M. Nagpur University, Prof. B.T.Deshmukh Research Award 2016, Prof. B.P.Chandra Research Award 2016, Outstanding Scientist-2015 award by Venus International Foundation, Advanced Materials Scientist Letter Awards-2011 by VBRI Press. He is co-author of 24 books/Chapters, three of which are of international level published by Springer Science, Heidelberg, New York, (Series: Springer Series in Materials Science), CRC Press, Taylor and Francis Group, Trans Tech Publication, Switzerland, Nova Science, New York, Lambert Academic Publishing respectively and one of book published on OLED by Elsevier Imprint Woodhead Publication, USA. He is life member of Society for Materials Chemistry, Luminescence Society of India, Indian Association for Radiation protection, Indian Laser Association, Indian Physics Association, International Association of Advanced Materials (IAAM), Vidarbha Environment Society, Nuclear Track Society of India and Indian Physics Teachers' Association, Society for Technologically Advanced Material of India (STAMI), Indian Science Congress.

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A review on the advancements in phosphor-converted light emitting diodes (pc-LEDs): Phosphor synthesis, device fabrication and characterization

Abstract

Introduction

Section snippets

Synthesis of phosphors

Effect of synthesis routes on the morphology of phosphors

Role of transition metal (TM) ions in LED phosphors

Role of lanthanide ions in LED phosphors

Red-emitting phosphors

Color-tunable phosphors

Characteristics of LED phosphors and the quality of light

Challenges in pc-LEDs

Newest trends in LEDs

Concluding remarks and outlook

Acknowledgement

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