THE PHOTO LUMINESCENCE CHARACTERISTICS
OF [A3RE(PO4)2 ]: Eu3+ PHOSPHORS
ABSTRACT:
Generally, the word Luminescence referred to as a cold light emission, which is different from incandesce light emission. In this article, we focused on the Photo- Luminescence properties of (A3RE(PO4)2): Eu3+ phosphors their applications in NUV based White Light Emitting Diodes and dosimeters . In many synthesis characterization Eu is widely used as a host because of its andady transition and Phosphate is widely as a environmental friendly elements, apart from this above material Yttrium and Ammonium also used to get cool light emission. The Eu3+doped K3Y(PO4)2was synthesized by combustion method and determined through XRD ,due to 4f-4f transitions of the Eu3+ion ,the obtained
phosphor shows a strong excitation charge transfer between 225 to 300 nm .
Keywords : Photo Luminescence, Combustion process, Furnace, Annealing,decay,
I.INTRODUCTION
Rare earth elements are used together with phosphate compounds for the lighting industry due to their luminescence (1). Alkali metal orthophosphates Rare Earth (A3RE(PO4)2) has become one of the exciting types of materials which can host and accommodate the rare earth metals activators. The phosphate-Oxygen compounds, interact to related units which require lower temperatures (2). Studies on improving the color quality and energy efficiency of phosphors have shown that rare earth metals have a higher performance in luminescence as compared to other chemical elements and compounds studied.
Rare metals used in lamps include terbium, yttrium, lanthanum, europium, cerium, and gadolinium since they have unique properties. These elements coat the inside of the lamp’s glass and act as activators of phosphate compounds to adjust or attain the desired lights and colors.
Their combinations either between the REE or with other elements give different colors in luminescence (3). Compounds of europium-yttrium produce red color, cerium- strontium-sulfide compounds give out blue while compounds of terbium-fluorine-zinc sulfide produce green light when activated by photons (4)&(5). Europium ions, however, is the best considered as an efficient red-light emitter. This is because it emits monochromatic light with a narrow band and has a long lifetime in the excited state (6) &(7). Phosphates of yttrium are used in luminescence due to their chemical durability, low
phonon energy, and perfect thermal stability. These properties enable them when doped with trivalent europium to have exceptional lumen maintenance, almost perfect red emission, and high quantum efficiency (8).
II.EXPERIMENTAL MATERIALS
The required materials for the synthesis of Eu3+doped K3Y(PO4)2 are
1.Potassium Nitrate (KNO3)
2.Yttrium Nitrate hexa-hydrate (Y(NO3)3.6H2O)
3.Ammonium tetra Oxo phosphate NH4H2(PO4)
4.Urea (NH2CONH2)
- Europium Nitrate hexahydrate (Eu(NO3)3·6H2O)
III. SAMPLE FORMATION
The Eu3+ activated K3Y(PO4)2 phosphors are undergoes combustion process
3KNO3+Y(NO3)3.6H2O+2NH4H2(PO4)+4NH2CONH2+Eu(NO3)3.6H2O
→ K3YEu(P04)2+20 H20+4C02+8N2
Materials are soluble in a Ethanol to get a state of paste,it changes to crucible further pre-heated at 550 degree’s (muffle furnace),white product is formed due to volumetric combustion for a 4 to 5’minutes duration, then it cooled to normal temperature of room to get a smooth powder by grinding. The smooth powder further heated at 800 degrees for 120 minutes duration which consider as annealing .The photoluminescence (PL) characteristics of the phosphors are observed with Spectro-fluorometer. The powder samples are recorded with a double beam spectrophoto meter.
IV.PHOTO LUMINESCENCE CHARACTERISTICS
When monitoring the emission peat at 617 nm, K3Y(PO4)2:Eu3+ phosphors excitation spectra have a strong spectra between 225-300 nm (CT) and 4f-4f sharp peak series of Eu3+ ions. The strong spectra is because of charge transfer from O2- → Eu3+ (9)&(6).Its wavelength sharp peaks range observed between ( 300 to 400 nm), at 320 nm,362 nm,382 nm and 395 nm for corresponding transitions (7 F0→5H6),(7 F0→GJ)4) (7 F0→5GJ ) and (7 F0→5 L6) which were characteristics of 4f – 4f Eu3+ ions . The phosphor’s absorption spectra band was 195-300 nm with a peak at the 236 nm. This simillar to charge moving to the Europium ions from the oxygen ions , shown in fig 1(a).
Figure 1. Photo Luminescence (a) spectra of Ex and Em (b) spectra of the K3Y(PO4)2:Eu3+ phosphors.
From Figure.1(b), It also observed that the emission spectra,due to 4f-4f characteristic transitions (5D0→7Fj),where (j = 1, 2, 3, 4) of the Eu3+ion ,bright and less bright intense peaks observed near 591 nm and 617 nm, 654 nm and 703 nm.(10),due to the 5D0→7F2. , the Eu3+ions reach the lower symmetrical region in the K3Y(PO4)2 , as the emission peak situated near 617 nm ,it also observed that the Eu3+ions equally occupy symmetrical & non symmetrical regions.
Figure 2. The different energies of the Eu3+– K3Y(PO4)2
From Figure. 2,it was observed that the different energy level transitions(possible involved) in the synthesis .When the sspecimen excited at a 395 nm wavelength, then the Eu3+ion is excited from ground to the 5L6 level ,during the emission process the Eu3+ion decays from 5L6 – 5D0 level.
The gap between 5D0→7FJ. (where J = 0, 1, 2, 3, 4) is high, the systematic decay procedure will not work and back to the ground state by releasing emission in the orange – red regions. The emission at 617 nm is observed which is because of the electric dipole transition of 5D0→7F2. .The 5D0→7F2 transition and the 5D0→7F1 transition luminescence pinnacle intensities of both similar , where the first transition dependent to the local symmetry,later one local symmetry due to in-sensitivity of a region
Conclusion
The excitation strong pinnacle of K3Y(PO4)2:Eu3+ with a range of 300-400 nm corresponds with the emission wavelength that is produced by NUV LED’s while emitting orange-red color.
the Eu3+ activated K3Y(PO4)2was synthesized by combustion method and it is observed by XRD. The obtained phosphor shows a strong excitation charge transfer spectra (225 – 300 nm) with some other strong pinnacles in between the range 300 to 400 nm because of 4f-4f transitions of the Eu3+ion.Therefore, it is evident that, rare earth elements luminescence can be used in the lighting industry, specifically K3Y(PO4)2:Eu3+ nanophosphor to produce an orange-red color in lamps.
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