A warm - orange light emitting eulytite type NaCaBi2-x(PO4)3: xSm3+ phosphor for white light emitting diodes (W-LEDs) application

Abstract

In this study, a series of samarium (Sm³⁺) activated eulytite type orthophosphate NaCaBi_2-x(PO₄)₃ i.e. (NCBP: xSm³⁺) phosphors with varying concentrations (x = 1–7mol%) of Sm³⁺ ions were successfully synthesized using high-temperature solid phase reaction routes. The crystal structure, surface morphology, elemental composition, band gap, thermal stability and optical properties of NCBP: xSm³⁺ were systematically investigated. The X-ray diffraction (XRD) pattern of host and Sm³⁺ doped NCBP exhibited a strong correlation with standard reference data (PDF 47–0836), confirming the successful synthesis of the samples. The band gaps of the host material and NCBP: 0.03Sm³⁺ were determined using diffuse reflectance spectroscopy, measuring 4.364 and 4.327 eV, respectively. The (Thermogravimetry analysis) TGA analysis indicates that the TGA curve stabilizes upon reaching 500 °C, confirming that the optimized phosphor maintains high thermal stability, even at elevated temperatures. In the NCBP: xSm³⁺ phosphor, under the excitation of at 405 nm, phosphors showed three significant emission peaks at 564 nm (green region), 600 nm (orange region) and 645 nm (red region) corresponding to the ⁴G_5/2 → ⁶H_5/2, ⁴G_5/2 → ⁶H_7/2, and ⁴G_5/2 → ⁶H_9/2 spectroscopic transition, respectively. The critical distance was calculated to be 20.33 Å and the energy transfer occurred due to multipolar interaction between activator ions. The Commission Internationale de l’Éclairage (CIE) chromaticity coordinates were found to lie in the deep orange-red region of the CIE diagram. These studies indicate that the NCBP: xSm³⁺ phosphor have well application prospects as a single component warm solid state lighting device, especially white-light emitting diodes (W-LEDs).