On the photoluminescence differences of Eu3+-activated layered perovskite La2Ti2O7 and A2La2Ti3O10 (A = Li, Na, K) phosphors for potential applications in white LEDs and plant growth lighting

To improve the quality of white LED and develop plant growth lighting, considerable efforts have been devoted to investigating red phosphor. Eu 3+ -activated phosphors are well-known red-emitting components due to their 5 D 0 - 7 F 1,2 transitions in various applications. It is also found that its 5 D 0 - 7 F 4 transition in the range of far-red wavelengths has potential applications in the fields of daily and agricultural lighting. In this study, two kinds of Eu 3+ -doped layered perovskite La 2 Ti 2 O 7 and A 2 La 2 Ti 3 O 10 (A = Li, Na, K) phosphors were synthesized by the solid-state method. The crystal structure, absorption, excitation, and emission spectra of all the samples were investigated in detail. Dissimilar luminescent behaviors of the studied samples were observed. Due to the different crystal structure and chemical composition of the host matrix, each compound exhibits a different emission spectrum. Specifically, Eu 3+ occupies a lower symmetric La 3+ site in A 2 La 2 Ti 3 O 10 (A = Li, Na, K) phosphors, resulting in an intense 5 D 0 - 7 F 4 far-red emission, while in La 2 Ti 2 O 7 :Eu 3+ , Eu 3+ gives a weak 5 D 0 - 7 F 4 emission. To the best of our knowledge, this is the first report that Eu 3+ exhibits a strong 5 D 0 - 7 F 4 far-red emission in the titanate host lattices with perovskite structure. Besides, A 2 La 2 Ti 3 O 10 :Eu 3+ (A = Li, Na, K) phosphors achieve higher photoluminescence efficiency than La 2 Ti 2 O 7 :Eu 3+ . Among them, the internal quantum efficiency of the optimized Li 2 La 2 Ti 3 O 10 :1.2Eu 3+ is about 84.7 %, and it has a better thermal stability (80 % at 125 °C). Furthermore, good photoelectric performances of red/white-LEDs fabricated by utilizing the representative Li 2 La 2 Ti 3 O 10 :1.2Eu 3+ as red/far-red components indicate that it has potential applications in indoor/outdoor lighting and plant growth lighting. This study provides a feasible way for developing efficient Eu 3+ -activated far-red optical materials.