Co-existence and unique co-emission properties of Eu3+/Eu2+ and Sm3+/Sm2+ in LiSrB9O15 host lattice

“Eu3+/Eu2+ and Sm3+/Sm2+ co-doped LiSrB9O15 phosphors” were synthesized by high temperature solid-state method in air atmosphere, and the XRD, crystal structure and photoluminescence properties were studied. The photoluminescence spectra show that the self reduction phenomenon of Eu3+ to Eu2+ and Sm3+ to Sm2+ do exist in LiSrB9O15:Eu and LiSrB9O15:Sm prepared in air atmosphere. Under the excitation of 248 nm, LiSrB9O15: Eu sample shows two bands of peaks. The sharp peaks in the range of 550–750 nm belong to the 4f-4f transition of Eu3+, and the wide peak from 350 to 450 nm centered on 367 nm belongs to the 4f-5d transition of Eu2+. Under 401 nm excitation, LiSrB9O15:Sm sample also shows two bands of peaks. The peaks in the range of 550–670 nm belong to the transition of Sm3+, and the peaks in the range of 680–780 nm belong to the transition of Sm2+. Then, we analyzed the lattice occupation of Eu and Sm ions in LiSrB9O15 matrix with the method of theoretical calculation, and explained why the self-reduction phenomenon can occur. Moreover, by changing the excitation wavelength of LiSrB9O15:Eu and LiSrB9O15:Sm samples, the luminescence color can be adjusted. The energy transfer from Eu2+ to Eu3+ was also found in LiSrB9O15:Eu3+/Eu2+ due to the spectral overlap. Finally, we found that Eu2+ has unique near ultraviolet luminescence in the range of about 367 nm. The near ultraviolet light in this range can just be used to trap and kill pests. This ultraviolet light can also promote plant growth and apply to ultraviolet medical treatment. Therefore, LiSrB9O15:Eu phosphor is a potential candidate in the preparation of ultraviolet LED lighting.