Temperature induced emission enhancement and investigation of Nd3+→Yb3+ energy transfer efficiency in NaGdF4:Nd3+, Yb3+, Er3+ upconverting nanoparticles

Inorganic upconverting nanoparticles that can be excited with 808 nm laser radiation are gaining much attention recently. Living tissues, as well as water do not heat up as intensively when embedded upconverting nanoparticles are excited under such wavelength if compared to commonly used 980 nm laser radiation for excitation. To this end, a series of NaGd0.995-xYbxNd0.005F4 nanoparticles were synthesized in order to investigate energy transfer efficiency between Nd3+ and Yb3+ dopants under 808 nm laser excitation to better suit biological applications. The impact of Yb3+ concentration increase on crystal phase formation as well as downconversion (DC) properties was investigated. Temperature dependent luminescence measurements in NIR region revealed that no thermal quenching of Nd3+−Yb3+ pair in NaGdF4 system was observed in the entire 77–500 K temperature range. Finally, Er3+ ions were introduced in the investigated system in order to obtain multiple excitation and visualisation tool with performance in both VIS and NIR regions. The effective energy difference (ΔE) was also calculated from the thermally coupled levels (TCLs) of Er3+. The promising results and observations of synthesized compounds will be discussed, as NaGd0.475Yb0.5Er0.02Nd0.005F4 has a potential to be used as a luminescent temperature sensor.