Abstract
In this study, we utilized a high-temperature solid-state reaction method to synthesize the red-emitting phosphors, namely Sr2ZnSi2O7:Sm3+ and Sr2ZnSi2O7:Sm3+/Eu3+. Characterization through X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX) revealed that the crystal structure of the as synthesized Sr2ZnSi2O7 samples aligned with the standard JCPDS no. 00-039-0235, featuring small irregularly shaped particles having a tetragonal structure with space group P-421m and space group number 113. The band gap values were determined using diffuse reflectance spectral (DRS) data. Photoluminescence (PL) emission spectra indicated efficient excitation of Sr2ZnSi2O7:Sm3+ and Sr2ZnSi2O7:Sm3+/Eu3+ phosphors under near-ultraviolet light (λex = 404 nm). The PL intensity of Eu3+ ions increased with increasing the concentration of Eu3+ ions, leading to a decrease in the PL intensity of Sm3+ ions. The energy transfer mechanism from Sm3+ to Eu3+ ions is mainly driven by dipole-dipole (D-D) interaction, as predicted using Dexter Reisfeld's approximation. As the concentration of Eu3+ ions increased, there was a reduction in the photoluminescence (PL) decay lifetimes. This decline affirmed the presence of the energy transfer (ET) mechanism from Sm3+ to Eu3+ ions, reaching a maximum transfer efficiency of around 23.11 % in the Sr2ZnSi2O7:Smx/Euy (x = 1.5, y = 5 mol%) phosphor. Computed CIE parameters under UV excitation showed a gradual shift towards the deep red region with increase in Eu3+ concentration. For Sr2ZnSi2O7: Smx/Euy (x = 1.5, y = 5 mol%) phosphor, the CIE color coordinates and color purity were (0.60120, 0.39485) and 95.62 %, respectively. These findings highlight the potential of the synthesized phosphors as solid-state emitters for warm white LED applications, featuring a low color-correlated temperature (CCT) value of 1724 K when stimulated with UV chips.
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