Zn2+, Sr2+, and Sm3+ tri-doped whitlockites: Luminescent materials with improved bioactive and antibacterial properties

Tri-doped phosphates Ca8‒xSrxZnSm(PO4)7 with the β-Ca3(PO4)2 (whitlockite) structure have been synthesized using solid-state synthesis. The crystal structure evolution from whitlockite to strontiowhitlockite was observed with Ca2+ → Sr2+ substitution. X-ray powder diffraction and second optical harmonic generation methods confirmed the symmetry inhomogeneity in the series, revealing a change in space group from R3̅c to R3̅m. In the Ca8‒xSrxZnSm(PO4)7 hosts, Sm3+ ions exhibited intense red emission according to 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2 transitions, coinciding with the biological window. The photoluminescence properties were study in detail, and the most intensive emission was found in sample with x = 3. All samples from the synthesized Ca8‒ xSrxZnSm(PO4)7 phosphate series showed high viability rates in aMSCs cell cultures compared to Journal Pre-proof 2 the control. The samples enhanced the osteogenic differentiation potential of aMSCs without significant differences depending on the Sr2+ concentration. The antimicrobial activity was study on five microorganisms: S. aureus, E. coli, P. aeruginosa, E. faecalis and C. albicans. All phosphate samples effectively inhibited bacterial growth, with samples x = 6 and 7.5 showing the highest effectiveness. The antimicrobial activity results from the synergistic effect of Ca2+, Sr2+ , Zn2+, and Sm3+ ions released into the solution at acceptable pH values. The study shows that both whitlockite and strontiowhitlockite structures can be considered as promising materials for bone substitutes, while the addition of the luminescent active Sm3+ ions will allow their use for bioimaging.