Thermal enhancement and quenching of upconversion emission in nanocrystals

Abstract

Surface chemistry of nanocrystals determines distinct thermal behaviours of upconversion emission.

High temperature (nano)thermometers based on LiLuF4:Er3+,Yb3+ nano- and microcrystals. Confounded results for core–shell nanocrystals

“…In order to gain additional insight into the mechanism for an increase in the measured emission lifetime we have performed thermal cycling tests on the LiLuF4: 2% Er 3+ , 18% Yb 3+ (core only) and LiLuF4: 2% Er 3+ , 18% Yb 3+ @LiLuF4 (6 shells) both in air and N2 atmosphere (by continuously flushing the sample chamber before and during the measurements) (Figure S12 -S15). [43] Figure Under N2 atmosphere, after an initial heating step to remove surface adsorbed water molecules, no enhanced luminescence at elevated temperature could be observed in both the core-only and core-shell systems, in agreement to earlier findings. [43] This suggests that removal of water molecules from the surface of the nanocrystals at higher temperatures causes the reduced quenching of Er 3+ .…”

Upconversion luminescence and temperature sensing properties of NaGd(WO4)2:Yb3+/Er3+@SiO2 core–shell nanoparticles

“…Although enhanced UC emission is not observed aer silica coating, the silica shell can somewhat passivate the surface and thus improve the thermal sensitivity. Ultrasmall NaLa(WO 4 ) 2 :Yb 3+ /Er 3+ UCNPs (sub-10 nm in size) was demonstrated to be thermally stable until $600 K. 15 In regard of present NaGd(WO 4 ) 2 :Yb 3+ /Er 3+ UCNPs in a relatively big size, it is reasonable to envisage that the silica coated UCNPs in our work can survive at higher temperatures. Besides the improvement of thermal sensitivity, the silica coating can extend the application of the material to high temperature environments.…”

“…Therefore, post-treatments are usually required. 12 In general, rare-earth oxides have better thermal stability and thermal sensitivity than uorides, [13][14][15] and thus are promising in bio-imaging and bio-sensing. Coating the nanoparticles with shell structures is a common approach to eliminate the surface defects and enhance the luminescence, so the optical thermometry performance of the nanoparticles can be improved.…”

Selective enhancement of upconversion luminescence for enhanced ratiometric sensing

“…We note that thermal quenching by local heating of Au nanodisks is not an issue because UCNP shows thermal enhancement of luminescence intensity with increasing temperature up to 200 C and the expected temperature increase under typical experimental conditions is much smaller than that. 41 We plotted the R/G ratios calculated from the simulated Purcell factors together with the measured R/G ratios in Fig. 4(c).…”