Synthesis, luminescence and photometric investigation of Sr${}_2$B${}_2$O${}_5$:Dy${}^{3+}$ phosphor for UV-based white LEDs

Undoped and a series of Dy${}^{3+}$ activated Sr${}_2$B${}_2$O${}_5$ phosphors were synthesized using the solution combustion technique and further annealed at 900 °C for better crystallinity. The powder X-ray diffraction results confirmed the single-phase monoclinic structure with the P21/c space group and the crystallite size was estimated using the Debye Scherrer formulation. The calculated value varied in the range of 45-49 nm for different molar concentrations of Dy${}^{3+}$ ions. The infrared spectra (IR) confirmed the presence of characteristic vibrational bands of BO${}_3$ units. The photoluminescence (PL) excitation spectrum of the phosphor contained characteristic peaks of the Dy${}^{3+}$ ions in the UV and near UV regions. The PL emission spectra exhibit four distinct emission peaks peaking at ${}^4$F${}_{9/2}$ → ${}^6$H${}_{15/2}$ (485 nm), ${}^4$F${}_{9/2}$ → ${}^6$H${}_{13/2}$ (575 nm), ${}^4$F${}_{9/2}$ → ${}^6$H${}_{11/2}$ (668 nm), and ${}^4$F${}_{9/2}$ → ${}^6$H${}_{9/2}$ (701 nm) corresponding to blue, yellow, red and brownish red emission, respectively. An increase in the optical bandgap values of 4.2 to 4.8 eV was observed with the addition of dopant ions (0.5-3.0 mol%) into the host matrix. In addition to the above mentioned parameters, the average lifetime of the phosphors was determined via decay plot and estimated to be 0.78 ms. The CIE (Commission International de'Eclairage) coordinates and Correlated color temperature (CCT) had respective values of (0.41, 0.43) and 3735 K which confirms the warm yellow light emission from the as-prepared phosphors. All of these findings demonstrated that the prepared phosphors are the auspicious candidate for usage in W-LEDs that generate yellow light.