Evaluation of relative beam–profile-compensated quantum yield of upconverting nanoparticles over a wide dynamic range of power densities

Abstract

The presented work uses a discrete strategy of beam profile compensation to evaluate the local internal quantum yield (iQY) of upconverting nanoparticles (UCNPs) at the pixel level of the beam...

Generalised analytical model of the transition power densities of the upconversion luminescence and quantum yield

“…Unlikely, the UCL of UCNPs typically does not show saturation, regardless of the number of excitation photons and number of energy transfers involved 21,28 . This behaviour seen in UCNPs, named as anomalous power (density) dependence for the first time by Suyver et al, has been extensively observed experimentally as shown in the literature [20][21][22][27][28][29][30][31][32][33] . Yet, analytical studies exploring the phenomenon are nonexistent, especially with regards to the different power density regimes and the thresholds between them.…”

“…Despite their poten-tial, the quantum yield (QY) of UCNPs remains low, especially at low excitation power densities required for biological applications 17 . The internal quantum yield (iQY) is often used as a figure of merit to characterise UCNPs, and is defined as the ratio of number of emitted photons to the number of absorbed ones [18][19][20] . At low excitation power densities the non-linear behaviour of UCL is more pronounced and, as a consequence, the iQY is power density dependent [20][21][22][23] , which adds further complexities to the evaluation of their efficiency.…”

“…The internal quantum yield (iQY) is often used as a figure of merit to characterise UCNPs, and is defined as the ratio of number of emitted photons to the number of absorbed ones [18][19][20] . At low excitation power densities the non-linear behaviour of UCL is more pronounced and, as a consequence, the iQY is power density dependent [20][21][22][23] , which adds further complexities to the evaluation of their efficiency. An accurate iQY evaluation is crucial for the development of optimal UCNPs, although, analytical and modelling studies on the excitation power density dependence of iQY are astonishingly scarce 22 .…”

“…The model proposed by the authors was based on two key works 21,28 using an elegant but simple rate equations model to describe the population densities of the energy states involved in the UC. Later on, their model was utilised in the implementation of a beam-profile compensation on experimental QY and to demonstrate the need of the compensation for an accurate evaluation of the iQY 20,23 . Apart from Liu et al's study on the ETU2, no study has been conducted on higher ETU processes.…”

Intensifying Upconverted Ultraviolet Emission towards Efficient Reactive Oxygen Species Generation

“…To overcome these issues, upconversion community accesses ultraviolet emission through size control, [32][33] lanthanide dopant tuning, [35] energy transfer manipulation, [36] core-shell structure engineering [37] and excitation pulse regulation. [38] Despite advances, it has met with limited success to obtain strong ultraviolet emission, especially in Nd 3 + -sensitized upconversion nanoparticles under 808 nm excitation. Very recently, our group developed an upconverted excitation lock-in strategy to achieve a remarkable enhancement in ultraviolet emission from Nd 3 + -doped upconversion nanoparticles.…”