New Na$_2$BaY$_4$F$_{16}$ matrix for up-conversion phosphors

In the process of investigation of NaF–BaF$_2$–YF$_3$ system, a new phase Na$_2$BaY$_4$F$_{16}$ (monoclinic crystal system, SSG $C2/m$, $Z$ = 2, lattice parameters $a$ = 12.1948(3) $\mathring{\mathrm{A}}$, $b$ = 8.2486(2) $\mathring{\mathrm{A}}$, $c$ = 7.0894(2) $\mathring{\mathrm{A}}$, $\beta$ = 119.893(3)$^\circ$ was prepared by solid-state synthesis. The first up-conversion luminescence studies have been carried out for Na$_2$BaY$_4$F$_{16}$:Yb$^{3+}$, Er$^{3+}$ under excitation at 980 nm. The highest luminescence energy yield for Na$_2$Ba(Y$_{0.87}$Yb$_{0.12}$Er$_{0.01}$)$_4$F$_{16}$ was 5.5% at a pump power density of 1 W/cm$^2$.