Tao Pang,Yanyan Wu,Yujian Zhang,Ronghua Jian,Junwen Mao,Hong Wang,Hai Guo
Although much effort has been focused on thermally enhanced upconversion (UC) luminescence, it remains a challenge to maintain or even enhance the UC luminescence of NaLnF4-based phosphors (Ln = Y, Gd, Lu) using a surface-independent strategy. In this work, we demonstrate that the effect of temperature on UC luminescence in NaGdF4:Nd3+/Yb3+/Er3+ nanocrystals is strongly dependent on the exciting wavelength. When excited using 808 nm radiation, the UC luminescence exhibits good resistance to thermal quenching. The reason is that, in this situation, the negative effect of multi-phonon decay can be fully compensated by the thermal enhancement in the transition cross-section and in energy-transfer rate. Our research reports a novel strategy for the anti-thermal quenching of upconversion luminescence, which is potentially applicable in the design of dynamic UC anti-counterfeiting as well as in NIR-I-responsive thermometers and nanoheating.
In this work, a sequence of Nd3+, Yb3+, and Er3+ tridoped SrF2 nanocrystals (NCs) is synthesized by a hydrothermal method. Both the efficient near-infrared downconversion luminescence (DCL) and visible upconversion luminescence (UCL) of the Er3+ and Nd3+ ions are simultaneously observed and systematically demonstrated under dual-wavelength excitation (808 and 980 nm continuous-wave lasers). Subsequently, the SrF2:Nd3+/Yb3+/Er3+ (15/4/0.2 mol %) NCs with the strongest luminescence were utilized for detecting the metal ion concentrations under 808 nm excitation. The results reveal that both the UCL and DCL gradually decrease as the metal ion concentrations increase, and high sensitivity is obtained for Cu2+ ions with a detection limit of 0.22 nM (∼650 nm) and 0.63 nM (∼976 nm). In addition, these SrF2:Nd3+/Yb3+/Er3+ NCs are further demonstrated to achieve a solid-state display under 980 nm excitation, exhibiting obvious “red” and “green” patterns by varying the doping rare earth ion concentrations.
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