AU2021102695A4 - A POTENTIAL BLUE-EMITTING PHOSPHOR Na2CaSiO4: Eu2+, Ce3+ PHOSPHOR WITH TUNABLE EMISSION FOR UV/NUV BASED WHITE LED AND SOLAR APPLICATIONS - Google Patents
A POTENTIAL BLUE-EMITTING PHOSPHOR Na2CaSiO4: Eu2+, Ce3+ PHOSPHOR WITH TUNABLE EMISSION FOR UV/NUV BASED WHITE LED AND SOLAR APPLICATIONS Download PDFInfo
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- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 title claims abstract description 47
- 238000001308 synthesis method Methods 0.000 claims abstract description 3
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 15
- 229910004762 CaSiO Inorganic materials 0.000 claims description 13
- 150000002500 ions Chemical class 0.000 claims description 12
- -1 europium ions Chemical class 0.000 claims description 9
- 229910052693 Europium Inorganic materials 0.000 claims description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- NHNBFGGVMKEFGY-UHFFFAOYSA-N nitrate group Chemical group [N+](=O)([O-])[O-] NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 6
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- 229910002651 NO3 Inorganic materials 0.000 claims description 4
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- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
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- WUOACPNHFRMFPN-UHFFFAOYSA-N alpha-terpineol Chemical compound CC1=CCC(C(C)(C)O)CC1 WUOACPNHFRMFPN-UHFFFAOYSA-N 0.000 description 1
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- SQIFACVGCPWBQZ-UHFFFAOYSA-N delta-terpineol Natural products CC(C)(O)C1CCC(=C)CC1 SQIFACVGCPWBQZ-UHFFFAOYSA-N 0.000 description 1
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- 229910052909 inorganic silicate Inorganic materials 0.000 description 1
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- 229910052747 lanthanoid Inorganic materials 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
- 238000004020 luminiscence type Methods 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
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- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
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- 150000004760 silicates Chemical class 0.000 description 1
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- 229910052712 strontium Inorganic materials 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 229940116411 terpineol Drugs 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
- C09K11/7783—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals one of which being europium
- C09K11/77922—Silicates
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
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- H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
- H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
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- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/054—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means
- H01L31/055—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means where light is absorbed and re-emitted at a different wavelength by the optical element directly associated or integrated with the PV cell, e.g. by using luminescent material, fluorescent concentrators or up-conversion arrangements
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- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
- H01L33/50—Wavelength conversion elements
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
2+ 3 A POTENTIAL BLUE-EMITTING PHOSPHOR Na2CaSiO4: Eu , Ce3+ PHOSPHOR
WITH TUNABLE EMISSION FOR UV/NUV BASED WHITE LED AND SOLAR
APPLICATIONS
2 3 The present invention relates to a potential blue-emitting phosphor Na2CaSiO 4 : Eu2, Ce'
phosphor with tunable emission which precisely use for white led and solar cell applications.
2+ 3+ In the present invention, blue-emitting phosphor Na2CaSiO 4:Eu2, Ce successfully
synthesized by sol-gel synthesis method. The XRD pattern confirms phase of synthesized
2+ 3+ phosphor and its luminescent properties are systematically studied. Na2CaSiO 4:Eu2, Ce can
be effectively excited by the 346 nm excitation, and create blue emission (440 nm). The
energy transfer from Ce3+ to Eu2+ has been detected in Ce3 and Eu2+ cooped Na2CaSiO 4. The
chromaticity coordinates of proposed phosphor are in blue region of CIE diagram.
1/4
I wa o a 30 3* 140 asao n so an TO
Figure 1
12003
1000
Soo 00
4400
200
0
Wavelength (nm)
Figure 2
Description
1/4
I wa o a 30 3* 140 asao n so an TO
Figure 1
12003
1000
Soo 00
4400
200
0
Wavelength (nm)
Figure 2
A POTENTIAL BLUE-EMITTING PHOSPHOR Na 2CaSiO 4: Eu2 , Ce PHOSPHOR WITH TUNABLE EMISSION FOR UV/NUV BASED WHITE LED AND SOLAR APPLICATIONS
Technical field of invention
Present invention, in general, relates to the field of solid state of lighting and morespecifically 2+ 3 to a potential blue-emitting phosphor Na 2CaSiO 4 : Eu , Ce 3+phosphor with tunable emission which precisely use for white led and solar cell applications.
Background oftheinvention
The background information herein below relates to the present disclosure but is not necessarily prior art.
In recent years, white light-emitting-diode (WLED) has attracted a lot of attention to facilitate the development of society in the field of lighting, because it's had amazing characteristics such as high efficiency and brightness, energy-saving, eco-friendly behavior, longer operational lifetime, low cost, no mercury pollution. Rare earth-activated phosphors have proved to be a promising candidate in the development of phosphor-converted LEDs (PC LEDs). Generally, it is possible to produce white light in three ways: (I) Combination of UV/NUV with single-phase red, green, blue (white-light-emitting) phosphors. (II) 3 Combination of a yellow-emitting YAG:Ce phosphor with a blue InGaN chip. This is most popular and commercially used method because this method has low fabrication cost and high luminous efficiency, but unfortunately, this method has also drawbacks like high correlated color temperature (CCT>7000 K), color-rendering index (CRI~ 70-80, ideal 100)and color deficiency in red region. (III)White light with excellent CRI value can be produced by combining UV LED chip in a reasonable proportion of red, blue and green LEDs, but its main problem is low blue emission efficiency.Therefore, the discovery of high performance phosphors, which is effectively excited by ultraviolet (UV), near-ultraviolet (N UV) and emits a suitable blue light, may be an effective finding for WLEDs.As the literature suggests, the performance of white LED-based devices depends on the luminescence properties of the synthesized phosphors. Therefore, we need to develop blue-emitting phosphor materials that can be efficiently excited by UV light.
In past decades, rare-earth activated luminescent phosphors become an essential theme of research because of their promising applicability in diverse fields such as photocatalysis, solid-state lighting, biomedical science, optical thermometer, and solar cell. Silicon-based solar cells have been the subject of a focus to make existing solar cells cheaper and compete effectively with other energy sources. There is a tremendous increase in the demand for silicon solar cells due to their widespread use in daily life, but limiting the conversion efficiency of Si-solar cell is spectrum mismatch between solar radiation and response spectrum of Si-solar cell has been a major problem.The thermalization and transmission of charge carriers generated by the absorption of high energy or low energy incident photons are the most significant loss of energy, which is wasted in the Si-solar cell.To improve the efficiency of the solar cell, suitable downconversion and upconversion phosphor materials can be used as a layer along with the solar cell, which are used to reduce the loss of energy as mentioned above.In the present work, we have demonstrated enhancement of the Si-solar cell efficiency by coating the synthesized downconversion phosphor in the upper side of the solar cell. In the last few years, efforts have been made to increase the efficiency of the solar cell by using downconversion phosphor.Recently, Fanchao Meng et al. reportedunder an empirical one-sun illumination, coated cells demonstrated a maximum enhancement of 3.6% (from 16.43% to 17.02%) in conversion efficiency relative to bare cells.Trupke et al reported enhancement in the efficiency of Si-solar cells upto 36.6%. P.S. David et al. reported enhancement in solar cell efficiency from 16.82% to 17.65%. S.K. Karunakaran et al. reported increment in the conversion efficiency (i) from 15.71% to 16.06%. So far, rare-earth activated phosphors have wide range of energy levels that give possibility of efficient spectral conversion. It has been found that there are various lanthanides ionsEu 2+ , Ce 33 , Tb3 + , Nd+3 Yb3+, Er et, which shows efficient down-conversion phenomenon to enhance the efficiency of solar cells.
As per the literature, alkaline earth silicates have attracted a lot of attention as hosts due to their stable crystal structure and flexible lattice sites. Rare earth activated silicate phosphors are known as highly efficient blue emitting phosphors under UV and Near UV radiation. Nowadays, A 2(A = Li, Na, K)M(M = Ca, Sr, Ba, Mg)Si04 systems have been extensively investigated for WLEDs by several scholars and scientists, because of their excellent thermal and hydrolytic stabilitiesthat meet the requirements for efficient host materials. However, to our best knowledge, there has been no investigation done on energy transfer mechanism between Ce3+ and Eu 2+ for Na2 CaSiO4 host, especially White LEDs and solar cell applications point of view. UV/NUV based blue emitting may be a useful blue component for 2+ the discovery of new phosphors for white LEDs. In the present work, Na2 CaSiO 4:Eu2+ Ce 3 +has been synthesized and its photoluminescence and I-V characteristics have been investigated.
Objective of the invention
An objective of the present invention is to attempt to overcome the problems of prior art and provide a potential blue-emitting phosphor Na 2CaSiO 4: Eu2, Ce phosphor with tunable emission which precisely use for white led and solar cell applications.
The present invention the novel Na 2CaSiO 4 :Ce 3 /Eu2+phosphors is synthesized by a sol gel method.
It is therefore an object of the invention shows Na 2CaSiO 4 :Ce 3 /Eu2+phosphors activatedwith Ce3 /Eu2+andemitted blue light.
These and other objects and characteristics of the present invention will become apparent from the further disclosure to be made in the detailed description given below.
Summary of the invention
Accordingly, the following invention provides a potential blue-emitting phosphor Na2CaSiO 4 : Eu2, Ce phosphor with tunable emission which precisely use for white led and solar cell applications. In present invention the novel Na2 CaSiO 4:Ce 37/Eu2+phosphors have been synthesized via a sol gel method. The XRD pattern of synthesized phosphor well matched with standard data and there is no impurity peak.Under UV light pumping, the Ce3 /Eu2+ single activated Na 2CaSiO 4emitted blue light. The energy transfer from Ce 3+ to Eu2+ has been detected in Ce3+ and Eu2+codoped Na2 CaSiO 4 .The chromaticity coordinates of proposed phosphor are in blue region of CIE diagram. Moreover, Ce3+ and Eu2+codoped Na2CaSiO 4phosphor is coated on solar cell enhances its efficiency 16.48% under the solar simulator and 20.89 % under direct sunlight. Hence all these results conclude that Ce3+ and Eu2+codoped Na2CaSiO 4phosphor is potential candidate for w-LEDs and solar cell efficiency enhancement.
Brief description of drawing
This invention is described by way of example with reference to the following drawing where,
Figure Ishows a graph of XRD pattern of Na 2CaSiO 4 phosphor. Figure 2 shows PL Excitation spectra of Na2 CaSiO 4 :1.5mol%Eu2+phosphor monitored at 446 nm emission wavelength. Figure 3 shows PL Emission spectra of Na 2Cax)SiO 4 :x.molEu2+ (x= 0.1, 0.5, 1.0, 1.5, 2.0)phosphors monitored at 345 nm excitation wavelength. Figure 4 shows variation in emission intensity with concentration of Eu2+ ions Na2CaSiO 4 :Ce 3+phosphor. Figure 5 shows PL Excitation spectra of Na2 CaSiO 4 :5mol%Ce 3+ phosphor monitored at 323 nm emission wavelength. Figure 6 shows PL Emission spectra of Na2 CaSiO 4 :x.molCe 3+ (x= 0.5, 1.0, 2.0, 5.0, 7.0, 10.0)phosphors monitored at 274 nm excitation wavelength. Figure 7 showsCIE chromaticity of (A) Na 2CaSiO 4 : 1.5mol%Eu2+ (B) Na2CaSiO 4 :5molCe 3 , 0.5molEu2phosphor (C) Commercial Blue LED. Figure 8 shows IV characteristics of Na2CaSiO 4 :5mol%Ce3 , 0.5mol%Eu phosphor under direct sunlight.
Detailed description of the invention
Exemplary embodiments a series of Eu/Ce doped or co-doped Na2 CaSiO 4 compound with different concentration of Eu2+ and Ce 3+ ions are synthesized via sol-gel synthesis method. AR grade Ca(N0 3 ) 2 , Na(NO3 ), SiO 2 .xH2 0, Eu 2 0 3 , Ce(N0 3 ) 3 .6H 2 0, HNO3 , citric acid and PEG (polyethylene glycol) are used as starting reagents. Firstly, Ca(N0 3) 2 , Na(NO3 ), SiO2 .xH 2 0 are dissolved in double distilled water. Here, Eu is available in the oxide form, so we are converted into nitrate form by dissolving stoichiometric amount of europium ions in a conc. solution of HNO 3 . Then, prepared Eu nitrate solution is added with Ca(N0 3) 2 metal ion solution. Further, Na(N0 3), SiO2 .xH 2 0 solutions added with metal ion solution. In this work, citric acid and PEG are used as chelating agent and surfactant in the stoichiometric ratio. Citric acid solution and PEG solation are added in the metal solution, then obtained mixture are stirred and heated at 80 °C to get form. Subsequently, obtained gel was burned at 550 C and black powder obtained. Then, obtained black powder transferred into ceramics crucible and heated at 650 C for 6 h to get final product. The prepared samples are then reduced in a charcoal atmosphere at 800°C for 7 h. The reduced samples are then used for further characterizations. Expected chemical reaction is takes place during synthesis as given below: Ca(N03 ) 2 + 2 Na(N0 3 ) + 4 Si0 2. xH 2 0 ->Na 2 CaSiO 4 + 4 NO2 T + xH 2 0 ... .. - (1) The XRD pattern of synthesized undoped Na 2CaSiO 4 compound is measured by using Rigaku miniflex d 600 X-ray diffractometer with Cu Ka radiation (X=0.154 nm). The photoluminescence properties of synthesized phosphors are recorded by SHIMADZU Spectrofluorophotometer RF-5301 PC equipped with a 150 W xenon lamp. The CIE Chromaticity coordinate is calculated by OSRAM SYLVANIA Color calculator with high accuracy.
The XRD pattern of synthesized undoped Na 2CaSiO 4 compound is presented in Fig. 1 and compared with standard ICSD Reference #98-002-4235. The XRD pattern of prepared material is well matched with standard data, which confirms materials are successfully synthesized. The measured diffraction peaks are sharp and intense, revealing the homogeneous and crystalline nature of the prepared material. It is reported that the substitution of Ca2+ (r = 1.12k) by the dopant/codopant ions having smaller radii Eu2+ r= 1.07 A) and Ce 3+ (r = 1.02A). The unit cell parameters are a=b=c= 7.48704, a=py= 90°, and the volume is 419.69 A 3 .
Fig.2 shows PL excitation spectra of Eu2+ activated Na2 CaSiO 4 phosphor. This PL excitation spectrum represents strong and broad excitation band centered at 345 nm under 446nm emission wavelength. At 345 nm excitation wavelength represents broad excitation band
2 )-> F6 5d 4 ranged from 230 to 450 nm due to the 4F7 (8S7/ (t2g) transition. The center of this broad excitation broad is around to 345 nm but excitation band lies to 450 nm. So according to this excitation spectra this phosphor can be well excited by UV light. Fig.5 represents PL emission spectra of Na 2Ca1 >)SiO 4 :xEu2+ (x = 0.1, 0.5, 1.0, 1.5, 2.0 mol %) phosphors monitored at 345 nm excitation wavelength. The PL emission spectra reveals broad emission peak ranged from 400 nm to 600 nm emission wavelength. The centered of this emission peaks monitored at 446 nm emission wavelength. This type of PL emission occurs because 4f5d 1 (t2g)->4f7(S7/2) transition of the Eu2+ions. As a result, the line shape of the emission did not change with the variation of Eu2+ concentration. In this PL emission spectra, it is cleared that emission peaks not shifted when the concentration of Eu2+ ions increased that means a similar profile can be identified in the emission spectra for different Eu2+concentration. The peak intensity is found to increase with the increasing Eu2+ concentration. Although the nature of the emission peaks are similar for all the dopant concentrations.
Fig. 4 reveals variation in emission intensity with variation the concentration of Eu2+ ions, there is an increase in the peak intensity when the dopant concentration varies from x = 0.1 to 1.5mol%. The optimum peak intensity of emission is recognized at x = 1.5 mol% and finally decreases. Which means the concentration quenching of Eu2+ in Na2CaSiO 4 occurs. Thus, the intensity of emission increases with increasing Eu2+ concentration. The PL emission spectra represents so according to this excitation spectra this phosphor can be well excited by UV light. This phosphor material may be very useful as blue component for white light emission. This phosphor material emit intense blue colour light this excited by UV-LED chip. This phosphor material is mixed with Green and Red colour emitting phosphor and it is useful for obtaining White light.
Fig. 5 shows PL excitation spectra of Ce 3+ activated Na2CaSiO 4 phosphor having broadband excitation ranging from 220 to 310 nm centered at 274 nm and 288 nm at emission of 323 nm due to 4f-5d transition of Ce3+ ions. Fig. 6 represents the PL emission spectra of Ce 3+activated Na 2CaSiO 4 phosphors are monitored under 274 nm excitation wavelength at room temperature. The concentration of Ce 3 +in the host Na2CaSiO 4 phosphor is varied as 0.5 mol%, 1 mol%, 2 mol%, 5 mol%, 7mol% and 10 mol%. The maximum intensity peak is observed at 323 nm for the 7 mol% of Ce 3 +doped Na 2CaSiO 4 phosphor and for other concentrations the intensity is observed less. According to PL emission spectra, it is observed that with increase in the concentration Ce 3 +ion in Na2 CaSiO 4 phosphor the intensity of the emission is increased and the maximum intensity is observed for 7 mol%. Under excitation at 288 nm, the emission spectrum due to the 5d-4f transition of Ce3+ in this host is observed. The emission consists of a peak at 323 nm and a shoulder at the low wavelength side, as shown in Fig. 7. Ce 3+ with a 4f electron configuration has two ground states of 2 F5 /2 and 2F7 /2 due to the spin-orbit interaction. The position of the Ce3+ emission band depends on crystal-field strength, covalency, and Stokes shift. It is a typical broad band shows 4f-5d transitions of Ce3+ ions.
Fig.8 revealed variation in emission intensity with concentration of Ce 3+ ions. Under 274 nm and 288 nm excitation, it was found that host material shows maximum intensity at 7 mol%. Further increase in the concentration of Ce3+in Na 2CaSiO 4 the emission intensity is decreased due to the concentration quenching. The spectral overlap between the emission of sensitizer and excitation of activator is necessary for energy transfer to take place. The sensitizer accepts the incoming photon and emits further, which is again absorbed by the activator ion to re-emit in visible region. Here in the present case, Ce3+ acts as sensitizer whereas Eu2+ acts as activator. The Ce3+ ions when excited by 274 nm emits in the broad band ranging from 310 to 550 nm, which is the excitation region for Eu2+ ions as shown in fig. 9.
Fig 10 shows PL excitation band of Na2CaSiO 4 :5mol%Ce3+, 0.5mol%Eu 2+ phosphor under 440 nm emission wavelength. The emission of Ce3+ in the 290- 400 nm range is almost encased in the excitation spectrum of Eu2 , which indicates the possible energy transfer from Ce3+ to Eu2+. On co-doping of Eu2+ ion with Ce3+, excitation spectrum get broaden than the individual PL excitation spectrum of Ce 3 3and Eu2 + as displayed in fig. 10 covers the range from 240 to 425 nm.
Fig. 11 shows the emission spectrum of Na 2CaSiO 4 : 5mol% Ce3+, xEu2+ (x= 0.1, 0.3, 0.5, 0.7, 1.0, 1.5 mol%)phosphors under 346 nm excitation, which is consists of a strong broad band centered at about 440 nm. It can be presumed that Eu2+ and Ce3+ ions occupy different types of sites in the Na 2CaSiO 4 host lattice, forming corresponding emission centers. Another possible reason for broad band can be explained by the crystal field splitting effect.
,3+ 2+ Fig. 12 concentration quenching curve of Na2CaSiO 4 :Ce , Eu sample by taking concentration of Ce3+ ion constant.The Commission International de I'Eclairage (CIE) 2+ chromaticity coordinates for (A) Na2 CaSiO 4 :1.5mol% Eu, (B) Na2 CaSiO 4 : 5mol% Ce 33 +
0.5mol% Eu 2+ and (C) commercially available blue LEDs are shown in Fig. 13. Fig. 13 represents CIE spectrum of (A) Na 2CaSiO 4 :1.5mol% Eu2 , (B) Na 2CaSiO 4 : 5mol% Ce3 +
0.5mol% Eu2+ and (C) commercially available blue LEDs. The CIE chromaticity coordinates of above-mentioned materials are located in deep blue region, corresponding to the point A,
B and C in Fig. 13, respectively. The calculated CIE chromaticity coordinates are listed in Table 1. Table 1: CIE Chromaticity coordinate of synthesized phosphors and Commercial Blue LEDs Sr. No Compound Name CIE Chromaticity Coordinate 1. Na2CaSiO 4 :1.5mol% Eu2 + A (0.1598, 0.2008) 2. Na2CaSiO 4 : 5mol% Ce", 0.5mol% Eu2 B (0.1513, 0.0386) 3. Commercial Blue LEDs C (0.1558, 0.0189)
To determine the efficiency of the solar cell of synthesized phosphor, experiments were carried out by IV characteristics at 12 o'clock in the afternoon at 40 C temperature and open condition at the Department of Physics, RTM Nagpur University, Nagpur. Temperature was measured by a simple thermometer. In the process of experimentation, firstly the characteristics of the blank silicon solar cell were measured in a solar simulator and sunlight at a temperature of 40 C. Subsequently, the synthesized phosphor is coated on a blank silicon solar cell as shown in Fig. 14. The coating process is done by the doctor blade method. In this work terpineol, ethyl cellulose, ethanol and acetic acid have been used with synthesized phosphor
The main electrical characteristics of a solar cell or module are summarized in the relationship between the current and voltage produced on a typical solar cell I-V characteristics curve. The intensity of the solar radiation (insolation) that hits the cell controls the current (I), while the increases in the temperature of the solar cell reduces its voltage (V). Solar cells produce direct current (DC) electricity and current time voltage equals power, so we can create solar cell I-V curves representing the current versus the voltage for a photovoltaic device.Solar Cell I-V CharacteristicsCurves are basically a graphical representation of the operation of a solar cell or module summarising the relationship between the current and voltage at the existing conditions of irradiance and temperature.
In the present invention, the IV characteristics of the coated solar cell are recorded under solar simulator and sunlight. We have plotted a graph between voltage (V) and current (mA). Then obtained curves are linearly fitted. The curve shows straight line with negative value of the slope. It is observed that the coating solar cell efficiency of the sample is increases up to
16.48% under the solar simulator and 20.89% under direct sunlight. In both situations the increase in solar cell efficiency is determined by the following formula:
Slope of coated cell EfficiencyS% = * 100 Slope of without coated cell
Claims (4)
1. A series of Eu/Ce doped or co-doped Na2 CaSiO 4 compound with different concentration of Eu2+ and Ce 3+ ions are synthesized via sol-gel synthesis method.
3 2. The potential blue-emitting phosphor Na2 CaSiO4 : Eu2, C cas claimed in claim 1 wherein the Ca(N0 3 ) 2 , Na(N0 3), SiO 2 .xH2 0 (reagent) are dissolved in double distilled water, Eu is in the oxide form, so it converted into nitrate form by dissolving stoichiometric amount of europium ions in a conc. solution of HN0 3
. 3 3. The potential blue-emitting phosphor Na2 CaSiO4 : Eu
2, C cas claimed in claim 1 wherein; Eu nitrate solution is added with Ca(N0 3) 2 metal ion solution;, Na(N0 3),
SiO2 .xH 2 0 solutions added with metal ion solution; Citric acid and PEG are used as chelating agent and surfactant in the stoichiometric ratio.
3
4. The potential blue-emitting phosphor Na2 CaSiO4 : Eu2, C cas claimed in claim 1 wherein; citric acid solution and PEG isolation are added in the metal solution, then obtained mixture are stirred and heated at 80 °C to get form; Subsequently, obtained gel was burned at 550°C and black powder obtained; Then, obtained black powder transferred into ceramics crucible and heated at 650 Cfor 6 h to get final product; the prepared samples are then reduced in a charcoal atmosphere at 800°C for 7 h. The reduced samples are then used for further characterizations.
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