Preparation and significant enhancement of upconversion luminescence of α-Ba2ScAlO5:Yb3+/Er3+ phosphors by Ca2+ ions doping

The intensity of upconversion luminescence (UCL) poses a significant challenge for oxides characterized by high phonon energy. Herein, a significant enhancement of red UCL is achieved through the introduction of an intermediate band (IB) in alpha-Ba2ScAlO5: Yb3+/Er3+ by Ca2+ ions doping. The absorption spectra verify the existence of the IB. The IB of alpha-Ba2ScAlO5: Yb3+/Er3+/Ca2+ increases the host's absorption of excited photons, provides more electrons for the excitation of Er3+, and realizes the enhancement of UCL emission. The optimal concentration of Ca2+ in alpha-Ba2ScAlO5: 0.2Yb(3+), 0.03Er(3+) is 0.15. Compared with undoped Ca2+ samples, the red and green UCL intensity of alpha-Ba2ScAlO5: Yb3+, Er3+, 0.15Ca(2+) increased by 48.2 and 10.6 times, respectively. The mechanism of Ca2+ enhanced UCL was investigated by analyzing the UCL spectra, absorption spectra and lifetime decay curves of alpha-Ba2ScAlO5: Yb3+/Er3+/Ca2+. The temperature-dependent UCL properties of alpha-Ba2ScAlO5: Yb3+/Er3+/Ca2+ were also studied by the H-2(11/2) (525 nm) and F-4(9/2) (667 nm) energy level radiation transitions. The observed linear correlation between luminescence intensity and temperature, coupled with its high sensitivity, indicates the promising potential for temperature sensing applications. This study not only opens a new avenue for enhancing UCL but also holds significant implications for sparking widespread interest in non-contact temperature sensing applications leveraging UCL.