Experimental optimization design synthesis for up-conversion luminescence performance in SrBi4Ti4O15: Er3+/Yb3+ red-green phosphors

Abstract

Er3+/Yb3+ co-doped SrBi4Ti4O15 crystalline powders were synthesized using the high-temperature solid-phase method. The crystal structure of the obtained phosphors was analyzed through x-ray diffraction (XRD), confirming the purity of all products such as SrBi4Ti4O15. Employing experimental design optimization theory, regression equations were established to correlate the Er3+/Yb3+ doping concentrations with the luminescent intensities. The genetic algorithm was utilized to compute the optimal solutions of the equations, resulting in Er3+ and Yb3+ doping concentrations of 3 mol% (molar fraction) and 20 mol% under 980 nm laser excitation and 3 mol% and 29.79 mol% under 1550 nm laser excitation. The up-conversion fluorescence emission spectra of the samples were measured under 980 nm excitation, revealing intense green emissions at 525 nm, 550 nm, and 662 nm, corresponding to the 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 energy levels, respectively. Under 1550 nm excitation, peaks corresponding to the same energy levels were observed at 523 nm, 548 nm, and 661 nm. The relationship between the up-conversion fluorescence and the laser operating current for the optimal samples under 980 nm and 1550 nm excitations was explored, indicating two-photon and three-photon processes, respectively. Detailed analysis and discussion of the up-conversion fluorescence mechanisms were conducted. Additionally, the relationship between the up-conversion fluorescence and the temperature for the optimal samples was investigated, revealing excellent temperature sensing characteristics under 980 and 1550 nm laser excitations. The CIE coordinates for the optimal samples were calculated as (0.3111, 0.6747) and (0.5254, 0.4671) under 980 nm and 1550 nm excitations, respectively.