The Photo -Luminescence characteristics of [A3REP(O4)2]: Eu3+ Phosphors

                                 The Photo -Luminescence characteristics of [A₃REP(O₄)₂]: Eu³⁺ Phosphors

                                 SRIDHAR GOUD ARELLI*^a   ANIL KUMAR ^b     SANJAY .J.DHOBLE ^c

                                           ^{a & b  DEPARTMENT OF PHYSICS,OPJS UNIVERSITY, CHURU,RAJ,INDIA}

                                                                      ^{c  DEPARTMENT OF PHYSICS,RTM NAGPUR UNIVERSITY,NAGPUR,M.S.INDIA}

                                                                       ^{Corresponding Author mail: arellisridharphysics@gmail.com}

                                                                   Abstract

 Luminescence referred to as cold light, which classified into many types, the cold light produced from different energy sources at low temperature. This article discusses the Photo- Luminescence properties of  (A₃RE(PO₄)₂): Eu³⁺  phosphors and their applications in  NUV based White Light Emitting Diodes and dosimeters. In many synthesis characterizations, Eu is widely using as a host because of its stable transition, and Phosphate is extensively using as an environmentally friendly element. Apart from this, some rare earth materials such as Yttrium, and Ammonium also used to get cold light emission. The Eu³⁺doped K₃Y(PO₄)₂was synthesized by combustion method and determined through XRD, because of the 4f-4f transition of Eu³⁺, the obtained phosphor show’s a reliable excitation charge transfer between 225 to 300 nm.

Keywords:  4f-4f transition, Photo- Luminescence, Combustion process, Furnace, Annealing, beam spectrometer.

                                                                      1..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 with related units that require lower temperatures (2). Recent Studies on improving the colour 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.

They used in lamps include Terbium, Yttrium, Lanthanum, Europium, Cerium, and Gadolinium. 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 colours.

Their combinations, either between the REE or with other elements, give different colours in luminescence (3). Compounds of Europium-Yttrium produce red colour, Cerium- Strontium-Sulfide compounds give out blue while mixtures of Terbium-Fluorine-Zinc Sulfide produce green light when activated by photons (4)&(5). Europium ions, however, are the best considered as an efficient red-light emitter. This combination emits monochromatic light with a narrow band and has a long lifetime in the excited state (6) &(7). Phosphates of Yttrium have 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 complete red emission, and high quantum efficiency (8).

                                                       2..EXPERIMENTAL MATERIALS

The required materials  for the synthesis of Eu³⁺doped K₃Y(PO₄)₂   are

1.The compound of Potassium- Nitrate  (KNO₃)

2. The compound of Yttrium-Nitrate -Hexahydrate [Y(NO₃)₃.6H₂O)]
3. The mixture of Ammonium Tetra Oxo Phosphate [ NH₄H₂(PO₄)]

4.Urea (NH₂CONH₂)

5. The compound of Europium -Nitrate -Hexahydrate [Eu(NO₃)₃·6H₂O]

3. SAMPLE FORMATION

The Eu³⁺  activated  K₃Y(PO₄)₂  phosphors are undergoing a 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 Ethanol to get a state of paste. It changes to crucible further pre-heated at 550 degrees (muffle furnace). The white product is forming due to volumetric combustion for a 4 to 5′ minute duration. It cooled to the average temperature of the room to get a smooth powder by grinding. The soft powder further heated at 800 degrees for 120 minutes duration, which considers as annealing. The photoluminescence (PL) characteristics of the phosphors are observing with Spectro-fluorometer. The powder samples are recording with a  double beam spectrophotometer.

                                                        4.PHOTO LUMINESCENCE CHARACTERISTICS

When monitoring the emission peak at 617 nm, K₃Y(PO₄)₂: Eu³⁺ phosphors excitation spectra have a reliable range between 225-300 nm (CT) and 4f-4f sharp peak series of Eu³⁺ ions. The energetic frequencies are because of charge transfer from O^2- → Eu³⁺ (9)&(6). Its wavelength sharp pinnacles range observed between ( 300 to 400 nm), at 320 nm,362 nm,382 nm and 395 nm for equivalent transitions (⁷F₀→⁵H₆),(⁷F₀→⁵D₄),(⁷F₀→⁵L₇) and (⁷F₀→⁵L₆) which were characteristics of 4f – 4f transition of Eu³⁺.  The phosphor’s absorption spectra band was 195-300 nm, with a pinnacle at the  236 nm. This similar to charge moving to the  Europium ions from the oxygen ions, shown in fig 1(a).

                                                               Figure 1. Photo Luminescence of

                         (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→⁷F_j), where (j = 1 to, 4) of the Eu³⁺ion, bright and less bright sharp pinnacles observed near 591 nm and 617 nm, 654 nm, and 703 nm. (10),

due to the ⁵D₀→⁷F_2.  The Eu³⁺ions reach the downward symmetrical region in the K₃Y(PO₄)_2, as the emission pinnacle situated near 617 nm. It also noticed that the Eu³⁺ions equally occupy symmetrical & non-symmetrical parts.

.

                                      Figure 2. The different energies  of the Eu³⁺– K₃Y(PO₄)₂

From Figure. 2, it was observed that the different energy level transitions(possibly involved)  in the synthesis. When specimen excited at 395 nm wavelength, then  Eu³⁺ion was excited from ground state to  ⁵L₆ level, during the emission process, the Eu³⁺ion decays from ⁵L_{6  –} ⁵D₀ level. The gap between ⁵D₀→⁷F_J.  (where J = 0 to 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 observed, which is because of the electronic dipole transition of ⁵D₀→⁷F₂. The ⁵D₀→⁷F₂ transition and the ⁵D₀→⁷F₁ transition luminescence pinnacle  intensity’s  of both similar, where the first transition dependent to the local symmetry, later one local symmetry due to in-sensitivity of a region

5.                           Conclusion

The sharp excitation pinnacle of  K3Y(PO4)2: Eu³⁺ with a range of 300-400 nm corresponds with the emission wavelength was generated by NUV LEDs while emitting orange-red colour.

The Eu³⁺ activated K₃Y(PO₄)₂was synthesized by the combustion method, and XRD observes it. 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 the 4f-4f transition of  Eu³⁺. Therefore, it is evident that rare earth elements luminescence useful to the lighting industry, specifically K₃Y(PO₄)₂: Eu³⁺ nano-phosphor, to produce an orange-red colour in lamps. 

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