Effect of Dy3+ Amount on the Structural and Luminescence Properties of LaNbO4:Dy3+ Phosphor Obtained by One-Step Spray Pyrolysis Process

Abstract

In this study, Dy 3+ -doped LaNbO 4 phosphors with a blue to white emission that can be tuned by varying the activator concentration were prepared by one-step spray pyrolysis process. According to the powder X-ray diffraction results, increasing Dy 3+ concentration favored the tetragonal phase. Slight changes were observed in the recorded Raman spectra as a function of Dy 3+ concentrations while SEM (scanning electron microscopy) micrographs presented similar profiles regardless the Dy 3+ amount. Investigation of Dy 3+ emission data in the visible range showed that rising the Dy 3+ concentration progressively shifted the emission towards the white color. All samples presented a wide excitation range from 254 to 475 nm. Keywords: spray pyrolysis, luminescence, lanthanum niobate IntroductionOver the last years, rare earth ions (RE 3+ ) have received increasing attention: solid-state materials doped with these ions can be applied in color screens, lighting, and optical devices. [1][2][3][4][5] The luminescence properties of these materials heavily depend on the structure of the electron energy levels. In RE 3+ , chemical binding affects these levels very little because orbitals 5s and 5p shield orbital 4f efficiently. 6 The f-f transitions in RE 3+ cause an array of emissions at different wavelengths, giving rise to a plethora of colors. However, f-f transitions are forbidden by the parity selection rule (Laporte rule), so they have low excitation efficiency. Excitation requires the use of a matrix and/or sensitizer that is able to absorb energy and transfer it to an emitting ion. 6,7 Lanthanum niobate (LaNbO 4 ) is a promising material for multifunctional applications. It has a band-gap of approximately 4.8 eV and emits blue and ultraviolet light when excited with ultraviolet (UV) radiation and X-rays, respectively. 8,9 Moreover, LaNbO 4 can transfer the absorbed energy to other emitting species, leading to different fluorescence emissions. 10,11 This oxide has been prepared by a number of techniques; for example, spray pyrolysis (SP), 12-14 solid-state reaction, 15-17 reactions in solution [18][19][20] and sol-gel route. 10,21 However, with an exception of our previously published work, 22 the authors were not able to finely control the size, shape, and distribution properties. Moreover, the SP process is completed in only several seconds, while other currently available methods require several hours or days to complete the process, even requiring a post annealing treatment. Briefly, SP process involves the vaporization of precursor solution followed by the drying, precipitation and decomposition in heated tubular furnace reactors. The stoichiometric ratio in the final prepared material is the same as the precursor solution, since the reaction and aggregation volume are confined in each generated micrometric droplet, which can be seen as a micro reactor. Therefore, particles synthesized by the SP process can be obtained on a laboratory or on an industrial scale. [22][23][24][25] Among the various material...

Luminescence properties of neodymium, samarium, and europium niobate and tantalate thin films

“…The emission peak at 615 nm was attributed to the forced electric dipole transition 5 D 0 → 7 F 2 , which was more intense than the peak at 595 nm that corresponded to the magnetic dipole transition 5 D 0 → 7 F 1 , suggesting that the Eu 3+ ions filled asymmetric sites in the lattice. [ 43,44 ] Similar PL spectrum of EuNbO 4 were reported with electric dipole 5 D 0 → 7 F 2 transition of Eu 3+ and the magnetic 5 D 0 → 7 F 1 dipole transition. [ 45 ] In ETO, the presence of the 5 D 0 → 7 F 0 transition band revealed site occupy of sites of Eu 3+ in the lattice and a line was also found at a lower wavelength (573 nm).…”

“…Among them, the excitation line at 395 nm, attributed to the 7 F 0 → 5 L 6 was a more predominant transition for ENO. [ 38–43 ] The bands in the 380–550 nm region match the Eu 3+ intra‐4f–4f transitions. The main excitation peaks at 362, 395 and 465 nm corresponded to the Eu 3+ changes 7 F 0 → 5 D 4 , 5 L 6 , and 5 D 2 , respectively.…”

“…The values of the luminescence parameters of the LnNO and LnTO films in this work were compared with those in the published literature listed in Table 1. [ 2,5,43,48–58 ] Lifetime is also an important parameter for luminescent materials. The average lifetimes of EuNbO 4 and EuTaO 4 powders obtained using the SSR method were found to be 327.0 and 376.0 μs, respectively.…”

“…[ 48,49 ] Luminescence lifetimes obtained in LNO powder‐doped Sm 3+ and Eu 3+ (LNO:Sm and LNO:Eu) were 570.0, 690.0, and 820.0 μs, respectively. [ 43,50,54 ] The lifetimes for the 5 D 0 → 7 F 2 transitions of Eu 3+ were calculated to be 799.0 and 830.0 μs for GNO:Eu prepared using hydrothermal and sol–gel methods, respectively. [ 55,56 ] The lifetimes of the tantalate powders prepared using the SSR method were found to be 81.5 and 1250.0 μs in NTO and TbTaO 4 , respectively.…”

Single-Phase Silicate Phosphors (Ba1.3Ca0.7−xSiO4:xDy3+) Doped with Dysprosium for White Solid-State Lighting

“…Here, the weak PL peak at 238 nm should originate from the host absorption band, whereas that at 294 nm from the O 2− ⟶ Dy 3+ transition [24,[48][49][50]. e other excitation peaks are attributed to the electronic transition 6 H 15/2 ⟶ 4 K 15/2 at 324 nm, 6 H 15/ 2 ⟶ 6 P 7/2 at 351 nm, 6 H 15/2 ⟶ 6 P 5/2 at 363 nm, and 6 H 15/ 2 ⟶ 4 I 13/2 at 382 nm, respectively [51][52][53][54][55][56][57][58]. Figure 5(c) shows the emission spectra of the host material (Ba 1.3 Ca 0.7 SiO 4 ) without any dopant, exhibiting a broad emission band at 482 nm from the self-trapped luminescent recombination.…”