Sites occupancy preference of Bi3+ and white light emission through co-doped Sm3+ in LiGd5P2O8

Bi3+, Sm3+-activated LiGd5P2O8 (LGPO) phosphors were prepared through high-temperature solid-state method. In LGPO host, there are 5 types of Gd crystallographic sites, named as Gd(1)/Gd(2)/Gd(3)/Gd(4), and Gd(5). Bi3+-activated LGPO phosphors exhibit 1 broad excitation band from 250 to 320nm centered at 293nm and a broad asymmetric emission band ranging from 350 to 600nm with the maximum value approximately at 409nm. It can be concluded from dual-emission spectra that Bi3+ may occupy 2 Gd sites and an obvious spectral blue-shift appeared with increasing Bi3+ content, which is caused by the intensity of crystal field of Bi3+ is decreased. Notably, through the calculation of each Gd-O chemical parameter, the environmental factor (h(e)) value of each Gd site can be obtained and it can be further inferred that 2 emission bands centered at 409/461nm are ascribed to Bi3+ ions which occupies Gd(3) and Gd(4) sites, respectively. Energy transfer from Bi3+ to Sm3+ ions in Bi3+/Sm3+ co-doped LGPO samples occurred and it realizes the color-tunable emission from cyan to yellow including white-light emission, through controlling Sm3+ content. Moreover, energy transfer mechanism between Bi3+ and Sm3+ ions is verified to be dipole-dipole interaction by analyzing the spectroscopic experimental results and the critical distance between them is calculated to be 8.22 angstrom by concentration quenching method. Finally, it is illustrated that Bi3+ and Sm3+ co-doped LGPO phosphors will be a promising candidate for n-UV chip pumped w-LEDs.