IndexIntroductionExperimentalResults and discussionConclusionIntroductionRare earth doped (RE) nanophosphors are widely used in light-emitting diodes (LEDs), field emission displays (FEDs), scintillators, medical imaging and in drug administration. The exceptional electronic and optical properties arise from the ff and fd transitions. However, many synthesized nanophosphors degrade rapidly when exposed to critical conditions. Hence, the need now is the synthesis of a nanophosphorus, which is stable in high vacuum with high brightness, thermal and chemical stability and possesses adequate mechanical strength. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an Original Essay Inorganic oxide-based nanophosphors have received considerable attention for generating color-tunable materials due to their characteristic high brightness, long life, low energy consumption, and eco-friendly nature. Earl Danielson in 1998, reported a new inorganic oxide compound (strontium-cerium oxide), synthesized by a combinatorial chemical procedure, which crystallizes in an orthorhombic crystal system with the space group Pbam (n. 55) and cellular parameters: a= 6.11897( 9) Å, b=10.3495(2) Å and c=3.5970(1). This strontium-cerium oxide (Sr2CeO4) is a blue-white emitting oxide and an excellent phosphor with high thermal and chemical stability, making it a promising matrix for various activators. The photoluminescence of Sr2CeO4 is due to energy transfer between O2 and Ce(IV) located in one-dimensional chains of the edge-sharing CeO6 octahedron. Regularly positioned luminescent elements govern the luminescent properties of the oxide, and the interaction of these regular optical centers that promotes spatial delocalization of the excitation energy is an important feature. Sr2CeO4 doped with rare earth ions (RE) results in the emergence of striking materials with a broad excitation band in the UV range and tunable emission. This is due to the effective transfer of excitation energy from the host to the doped centers emitting colors of another spectral range. Furthermore, the luminescence properties depend on the RE dopant used and the dopant concentration. Several methods have been developed for the synthesis of efficient single-phase RE-doped luminescent Sr2CeO4 nanophosphors. These procedures are still evolving due to various drawbacks of stability, control over size and morphology. In a contribution aimed at overcoming these limitations, here we reported for the first time the synthesis of luminescent rod-like Sr2CeO4:Eu3+(mol% Eu=0, 0.1, 0.5) ,1, 1.5, 2) using the of combustion. A systematic methodology was followed for the synthesis of this highly stable nanophosphorus. Eu3+ was chosen as it acts as a good activator ion with red or red-orange emission in various hosts. The results show a generation of white light at lower concentrations, while a red luminescence at higher concentrations of the dopant. The report also covers the synthesis and characterization aspects of RE-doped complex along with their potential use in lighting and optoelectronic devices. The source of Sr, Ce, Eu was strontium nitrate (Sr(NO3)2).9H2O; 99.99%, Merk Ltd), cerium nitrate (Ce(NO3)3.6H2O; 99.99% Sigma Aldrich Ltd) and europium nitrate (Eu(NO3)3.xH2O; 99.99% Sigma Aldrich Ltd) respectively . Numerous fuels such as citric acid, glycine, oxalic acid, oxalyl dihydrazide (ODH), urea, etc. have been used for the synthesis of nanophosphorus materials. Citric acid produces a bulky, soft product, while urea is environmentally friendly, low cost and readily available.used compared to hydrazine-derived fuels. Stoichiometric quantities of strontium, cerium, europium nitrate were taken into a 200 ml beaker to synthesize Sr2-xCeO4:Eux3+ (x=0.1-2mol %) nanophosphors, taking into account the Eu3+ ions replacing the Sr2+ ions in the structure . Required amount of urea was added to the mixture and 20 ml of deionized water was added to dissolve the mixture, the mixture was well dispersed using magnetic stirrer at 80 °C for 10-15 minutes. The stoichiometry of the redox mixture used for combustion was calculated using the total oxidizing and reducing valencies of the compounds. By balancing the total oxidizing and reducing values ​​of the compound, the stoichiometry of the redox mixture for combustion was calculated. The homogeneous mixture was introduced into the preheated muffle furnace maintained at 550+10°C, first the solution was boiled and subjected to dehydration and subsequently with the release of large quantities of CO2, H2O, N2 gases. Then a spontaneous spark occurred and underwent a combustion reaction. The whole process was completed in 10 minutes. The foamed product was slowly cooled to room temperature, the product was crushed in a mortar and pestle, and then calcined at 1000°C for 4 hours. The complete combustion equation of the redox mixture used for the synthesis can be written as: 12 Sr(NO3)2).9H2O + 6 Ce(NO3)3.6H2O + 34CH4N2O → 6 Sr2CeO4 + 34 CO2 + 68H2O + 55N2 12Sr1-x ( NO3)2 + 6Ce(NO3)3.6H2O + 34CH4N2O + xEu(NO3)3.XH2O → 6Sr2CeO4:xEu + 55 N2 + 104 H2O + 34CO2 2.2 Characterization and instrumentation The phase purity and crystalline structure of the products obtained were characterized by the X-ray powder, to obtain the diffraction data, ray diffraction is used, using an . XRD patterns were collected in the range 10°<2θ<70°. The UV-visible absorption spectrum was recorded on the Shimadzu 2600 dual-beam UV-visible spectrophotometer. Photoluminescence (PL) measurements were performed on a Cary Eclipse fluorescence spectrophotometer (Agilent Technologies) equipped with a 450 Xenon lamp W as excitation source. The morphology of the product was examined using FE-SEM (Hitachi SU 70). All measurements were performed at room temperature. Color coordinates were calculated by the CIE Chromaticity color calculator. Results and discussion Pure Sr2CeO4 and Sr2-xEuxCeO4 doped phases (x=0.1-2 mol%) were synthesized by low-temperature combustion method, in steps in order to modify the structural properties and as a consequence, luminescence through the replacement of Sr2+ ions with Eu3+ ions in the structure. The compounds are highly crystalline, very pale yellow in color, stable in air, insoluble in water. XRD analysis The diffraction models of the SR2Ce4 synthesized drug addicted with EU3+ ions to 0.5% in hinted mols at 1000 ° C are illustrated in Figure 1. On the basis of the analysis of diffraction of the X -rays measured and in the comparison of the data shown, indicates the formation of a single orthorhombic phase with the Pbam space group. The introduction of Eu3+ dopant ions into the crystalline structure of the oxide is confirmed without notable distortions in the diffraction pattern. This confirms that Eu3+ ions successfully exist in the lattice site rather than the interstitial site. Dopant site substitution can be inferred from the percentage difference in the ionic radii of the host and dopant ions. In our system the ionic radius of Eu3+ is 0.947Å, while that of Se2+, Ce4+ are respectively 1.18Å, 0.87Å below the number ofcoordination (CN=6). The percent difference in ionic radii (Dr) between the host and doped ions is calculated using the equation. Dr = Rh(CN) -- Rd(CN) Rh(CN) Where CN is the coordination number, Rh(CN) is the radius of the guest cations, Rd(CN) is the radius of the doped ion. The calculated value of Dr between Eu3+ and Sr2+ on six coordinated sites is 19.74%, while that between Eu3+ and Ce4+ is -8.85%. This shows that the Eu3+ dopant would clearly replace the strontium sites. Therefore Eu3+ most preferably replaces Sr2+ rather than Ce4+. Similar results have been reported for various rare earth ions doped with Sr2CeO4phosphorus. Atomic mobility causes grain growth which results in improved crystallinity since all samples were calcined at higher temperature (1000°C). The average crystallite size was estimated by the Debye-Scherrer method. D= [ 0.9λ ] Βcosθ Where D is the average crystallite (grain) size, the factor 0.9 is Scherrer's constant, λ denotes the wavelength of X-ray radiation, β is the half maximum of full width (FWHM) and θ the Bragg angle of an observed diffraction peak. The particles were found to be smaller in the nanometer range, and some large grains were also present. This resulted in a slight deviation of Scherer's calculations. The obtained nanophosphorus was composed of nanocrystallites with an average size of 64.16 nm. The increase in dopant concentration introduces deformation and alteration of the periodicity of the lattice which results in the decrease of crystalline symmetry. Crystallite size was also calculated from powder X-ray diffraction line broadening (β) using the analysis described by the Williamson and Hall (WH) plot. βcosθ= ɛ(4 sinθ) + 1 /D λ λ Where β is the FWHM in radians, ɛ is the developed strain, and D is the crsyatallite size. The equation represents a straight line between 4Sinθ/ λ (X-axis) and β cosθ/ λ (Y-axis). The slope of the line gives the inhomogeneous strain (ɛ), and the intercept (1/D) of this line on the Y-axis gives the crystallite size (D). The particle size calculated by WH was 54.64 nm. The dislocation density was estimated using the relationship δ=1/D2. There is a slight difference in crystallite size determined from WH plots and those calculated using Scherrer's formula. The small variation is due to the fact that in the Scherrer formula the strain component is assumed to be zero and the observed broadening of the diffraction peak was considered only as a result of the reduction in grain size. FE-SEM analysis shows a soft and porous agglomerated morphology due to combustion synthesis. However, the FE-SEM images obtained in this study show rod-like structures with nanometer diameters. During combustion synthesis, the temperature immediately rises to a higher level, remains there for a few seconds, and rapidly drops to a lower temperature. In a very short period of time the crystals undergo a rapid process of shape evolution to form various morphologies. UV-Vis Absorption Spectroscopy Optical absorption spectra were recorded in the wavelength region of 200–450 nm. In all samples, a flagrant absorption peak is observed around 330 nm and 260 nm, while peaks at 220 nm are present in concentrations higher than 0.1 mol% of dopant. By changing the dopant concentration, the absorption wavelength changes slightly, as seen by increasing the dopant concentration, the absorption edge shifts towards a longer wavelength. The optical energy gap, Eg of the doped samples, was calculated using the Tauc relationship. αhν ~ (hν -Eg)n Where hν is the photon energy and α is the optical absorption coefficient near the fundamental absorption edge. The absorption coefficient α is calculated from the optical absorption spectra. Optical band gap energy values ​​are obtained by plotting (αhν)n Vs hν in the high absorption range followed by extrapolating the linear region of the plots to (αhν)n=0. Eg is the optical band gap and n is the constant associated with the different types of electronic transition n = ½, 2,3/2, 3 for direct allowed, indirect allowed, forbidden and indirect forbidden transition respectively. The optical energy band gap of nanophosphors varies between 3.08 and 3.21 eV. The variation of Eg values ​​with different concentration of Eu3+ in Sr2CeO4 is mainly attributed to structural defects such as vacancies, degree of structural disorder in the lattice, which is capable of changing the distribution of intermediate energy levels within the band gap. Photoluminescence studies Luminescence properties of single-phase Sr2CeO4 blue light generation. The figure shows the excitation spectra of strontium-cerium oxide. It consists of two peaks, a broad band at 260 nm and a shoulder at 340 nm. Due to the different types of Ce4+ and O2- lattice bonds, the spectra show two excitation peaks due to different charge transfer transitions. The characteristic emission of the blue phosphorus Sr2CeO4 is linked to CT phenomena from the orbitals of the O2- ions to the empty 4f shell of the Ce4+ ions. The highest energy band (245 nm) originates from the O1 to Ce4+ transition, where O1 is the terminal oxygen ion in the Sr2CeO4 structure and the peak at 330 nm results from the CT transition between the equatorial oxygen ion and the Ce4+ ion (O2-to Ce4+ ). The figure shows the emission spectra of strontium-cerium oxide. It is a simple broad band with the center located at 475 nm attributed by the charge transfer emission of Ce4+, in Ce4+ the 4f level is vacant, so the only possible transition is where an electron is excited by the oxygen ligand to the Ce4+ ion: a charge transfer transition. Under UV radiation, ground state excitation occurs in one of the excited states, t1u-f or t1g-f, associated with two groups of O2- ions (equatorial and terminal). Due to the t1u-f spin forbidden transitions, the related absorption or excitation band is less intense than the band connected to the t1g-f transition. The emission in the 400-600 range is linked to the radiative relaxation process from the excited CT state of the CeO6 complex. It is associated with a reduction in crystallite size. It directly affected the energy band gap of Sr2CeO4, widening the distance between the ground state and the excited CT states. Luminescence properties of doped Sr2CeO4:Eu3+ (0-2 mol%) are observed, emitting white light at low concentration and red light at higher concentration. Excitation spectra were recorded by setting the maximum emission intensity of Eu3+ (615 nm) as the observation wavelength for the entire dopant concentration. The recorded spectra show the same characteristics for all measured samples with a broad band in the range of 200-320 nm and a shoulder at 340 nm, which are assigned to the Ce4+-O2-CT transition of undoped Sr2CeO4. Eu3+ ions in the oxide exhibit their own CT states, they can also take part in ET. The broadband peak around 260 nm is due to the overlap of the charge transfer bands from oxygen to europium (O-Eu) and the host band (Ce-O). The 4f-4f intra-configurational transitions of Eu3+ correspond to weaker peaks in the 320-450 nm range. The transitions 7F0à5H3, 5L9, 5L7, 5L6 and 5D4 correspond to peaks at 320,360,380,395 and 420 nm, respectively. The increasing concentration of Eu3+ ions.