Investigation on the determinant of upconversion luminescence efficiency and temperature measurement sensitivity based on AWO4 (Ba, Sr, Ca, and Mg): Er3+/Yb3+ microcrystals

In this work, a comparative study of the upconversion (UC) luminescence properties of ${{\rm Er}^{3 +}} {-} {{\rm Yb}^{3 +}}$-co-doped ${{\rm AWO}_4}$ (${\rm A} = {\rm Ba}$, Sr, and Ca) scheelite phosphors and ${{\rm Er}^{3 +}} {-} {{\rm Yb}^{3 +}} $-co-doped ${{\rm MgWO}_4}$ wolframite phosphors is reported. Under 980 nm excitation, all the samples emit green and red emissions. The ${{\rm Er}^{3 +}} {-} {{\rm Yb}^{3 +}}$-doped ${{\rm MgWO}_4}$ phosphor has a higher UC emission intensity. Furthermore, the optical temperature sensing properties in ${{\rm Er}^{3 +}} {-} {{\rm Yb}^{3 +}}$-co-doped ${{\rm AWO}_4}$ (${\rm A} = {\rm Ba}$, Sr, Ca, and Mg) phosphor samples are investigated. The relative sensitivity (${{\rm S}_r}$) based on thermally coupled levels (TCLs) increases gradually with an increase in matrix phonon energy. The absolute sensitivity (${{\rm S}_a}$) values of the samples are accurately predicted by the chemical bonding parameter (${{\rm f}_c}$). The results of the correlation between the UC luminescence properties and the microscopic crystal structure, and the relationship of the temperature sensitivity and the host parameters, provide us with a guiding insight for the selection of a host material with ideal temperature measurement capability.