Intense red up-conversion luminescence and temperature sensing property of Yb3+/Er3+ co-doped BaGd2O4 phosphors

BaGd2O4: x mol% Yb3+/y mol% Er3+ phosphors with intense red up-conversion luminescence were synthesized by high temperature solid-state method. The maximum intensity ratios of the red emission to the green ones were achieved to be 50.3 and 158.7 under 980 nm and 1550 nm excitations, respectively. The absolutely sensitivities were obtained to be 0.42% K−1 at 573 K and 0.18% K−1 at 298 K by using the fluorescence intensity ratio of the two green emissions and the Stark sub-peaks of red emissions, which indicates that BaGd2O4: Yb3+/Er3+ phosphor has potential application in the field of temperature sensing. [Display omitted] •Intense red UC luminescence was obtained in BaGd2O4: Yb3+/Er3+ under 980 nm and 1550 nm excitations.•Dependence of UC luminescence properties on Yb3+ and Er3+ concentrations were discussed.•Energy transfer from Er3+ to Yb3+ was investigated via fluorescence lifetime measurement excited at 1550 nm.•Temperature sensing property was studied via FIR technology using both red and green emissions excited at 980 nm. In this study, intense red and extremely weak green up-conversion (UC) luminescence was obtained in BaGd2O4: x mol% Yb3+/y mol% Er3+ phosphors under the excitations of 980 nm and 1550 nm. The corresponding maximum integrated intensity ratios of the red to green UC emissions are 50.3 and 158.7, respectively. The UC luminescence mechanisms upon different excitations were discussed. It was confirmed that two-photon and three-photon processes were responsible for both the red and green UC emissions excited at 980 nm and 1550 nm, respectively. The energy transfer efficiency from Er3+ to Yb3+ was calculated according to the fluorescence lifetime measurement under 1550 nm excitation. Temperature sensing based upon the thermally coupled energy levels 2H11/2/4S3/2 as well as thermally coupled Stark sublevels of 4F9/2 level of Er3+ was investigated under the excitation of 980 nm. The maximum absolute sensitivities were respectively obtained to be 0.42% K−1 at 573 K and 0.18% K−1 at 298 K. Our results indicated that BaGd2O4: Yb3+/Er3+ phosphors might be a kind of promising red UC phosphors with optical temperature measurement function.