Enhancement of upconversion luminescence using photonic nanostructures

Abstract

<jats:title>Abstract</jats:title><jats:p>Lanthanide-based upconversion materials convert low energy infrared photons into high energy visible photons. These materials are of interest in a myriad of applications such as solar energy harvesting, color displays and photocatalysis. Upconversion nanoparticles (UCNPs) are also of interest in biological applications as bioimaging and therapeutic agents. However, the intrinsic conversion efficiency of UCNPs remains low for most applications. In this review, we survey the recent work done in increasing the upconversion emission by changing the local electric field experienced by the UCNPs using photonic nanostructures. We review both the underlying theory behind this photonic manipulation as well as experimental demonstrations of enhancement. We discuss the recent developments in the more common plasmonic designs as well as the emerging field of dielectric nanostructures. We find that improvements in design and fabrication of these nanostructures in the last few years have led to reported enhancements of over three orders of magnitude. This large enhancement has been achieved in not only nanostructures on films but also in nanostructures that can be dispersed into solution which is especially relevant for biological applications.</jats:p>

Decay Rates of Plasmonic Elliptical Nanostructures via Effective Medium Theory

“…where ∆ is the distance between the exited atom and the NP and k o is the wave number which is defined as √ ε m ω c [9,37], where ω is the angular frequency and c is the speed of light.…”

“…Then, the first three modes with are taken to use the mentioned expressions of Equation (23) for both the ellipsoid and the spheroid [ 62 ] and Equation (24) for the sphere [ 26 ], to calculate the normal non-radiative decay rate. where is the distance between the exited atom and the NP and is the wave number which is defined as [ 9 , 37 ], where is the angular frequency and c is the speed of light.…”

“…In linear photoluminescence, the electric field enhancement ( γ E ) is defined by Equation (25). where E is the local maximum of electric field, and E o is the amplitude of the input source electric field and N is an exponent order which is approximated to be 2 [ 37 ] and Equation (26) is a general relation that is valid for all targeted geometries; ellipsoid, sphere, and spheroid. The polarization factor ( ) varies from one shape to another as explained before in Table 1 .…”

“…Moreover, the metallic nano-radiator quantum dot can be employed as an amplifier to the plasmonic surface by using the emission radiation [29,30]. The plasmonic metallic nanostructures; such as gold, silver, and copper can be embedded in many applications such as solar cells [31][32][33][34][35][36], up conversion [32,[37][38][39], light emitting diodes (LEDs) [40,41], lasers and laser printing [42][43][44][45], sensors and photodetectors [46][47][48][49]. Moreover, the plasmonic nanoparticles aid to slow down the speed of light which can enhance both absorption efficiency and optical coupling in the waveguide-cavity for optical communication networks and sensing applications [25,[48][49][50][51][52][53].…”

Selective enhancement of upconversion luminescence for enhanced ratiometric sensing

“…[10][11][12][13][14] Plasmon enhancement of luminescence, oen referred to as the Purcell effect, arises from the increased photon density of states due to the plasmon resonance. 15,16 The actual enhancement factor is determined by the combination of the Purcell effect and the unavoidable quenching by metals. In any case, since luminescence is a linear process, the plasmon-enhanced luminescence intensity is linearly proportional to the local intensity enhancement factor, which is determined by the details of the nanostructure geometry and materials used.…”