Study of structural and spectroscopic characteristics of novel color tunable yellowish-white Dy3+ doped Gd4Al2O9 nanophosphors for NUV-based WLEDs

Urea-assisted solution combustion (SC) synthetic method is employed to prepare a series of yellowishwhite light emitting Dy3+ doped Gd4Al2O9 (x = 1-6 mol%) phosphors. Phase identification and refinement parameters of designated nanomaterials are analyzed by means of Rietveld refinement technique. All doped samples are structured into monoclinic crystal system with P21 c space group. Scherrer's formula and Williamson-Hall (W-H) linearly fitted method are employed to enumerate the crystallite size that are observed in the domain of nano-scale. The transmission spectrum of diffused reflectance is utilized to calculate the optical energy band gap of optimized sample Gd3.97Dy0.03Al2O9 that come out to be 5.11 eV. TEM micrograph discloses the existence of non-uniform agglomerated particles. The photophysical characteristics of doped phosphors are analyzed by exploiting their photoluminescence excitation (PLE) and emission profiles. The most intense excitation peak is found to be at 351 nm, which is meticulously harmonized with the distinctive wavelength of commercialized near ultra-violet (NUV) based LED chips. The emission profile of all doped samples possesses sharp emission lines centered at 481, 573, and 667 nm, which are ascribed to F-4 (9/2) -> H-6 (15/2) -> (4) F (9/2) -> H-6 (13/2) , and F-4 (9/2) -> H-6 (11/2) intraconfigurational transitions of Dy3+ ion, correspondingly. The emission decay curves are well fitted with biexponential function and in good agreement with findings of the refinement analysis viz. existence of two non-centrosymmetric sites attained by the Dy3+ ions. Auzel's model is used to estimate the radiative lifetime (tR= 5.14356 +/- 0.65104 ms). The chromaticity coordinates and correlated color temperature (CCT) values for all doped samples are found close to standard white coordinates, thus proved them a potential candidate in single-phase phosphor converted WLEDs.

Automated summary

Urea-assisted solution combustion method was used to synthesize yellowish-white light emitting Dy3+ doped Gd4Al2O9 phosphors. Rietveld refinement analysis showed that all the doped samples have a monoclinic crystal structure. The crystallite size was determined using Scherrer's formula and Williamson-Hall linear fitting method. The optical energy band gap of the optimized sample was calculated to be 5.11 eV. TEM micrograph revealed the presence of non-uniform agglomerated particles. Photoluminescence excitation and emission profiles of the doped phosphors were analyzed and found to have intense excitation peak at 351 nm and sharp emission lines at 481, 573, and 667 nm. The chromaticity coordinates and correlated color temperature values indicated that the doped samples can be used in single-phase phosphor converted WLEDs.