In recent years, lanthanide-doped nanothermometers have been mainly used in thin films or dispersed in organic solvents. However, both approaches have disadvantages such as the short interaction lengths of the active material with the pump beam or complicated handling, which can directly affect the achievable temperature resolution. We investigated the usability of a polymer fiber doped with upconversion nanocrystals as a thermometer. The fiber was excited with a wavelength stabilized diode laser at a wavelength of 976 nm. Emission spectra were recorded in a temperature range from 10 to 35 ${}^{\circ }$C and the thermal emission changes were measured. Additionally, the pump power was varied to study the effect of self-induced heating on the thermometer specifications. Our fiber sensor shows a maximal thermal sensitivity of 1.45%/K and the minimal thermal resolution is below 20 mK. These results demonstrate that polymer fibers doped with nanocrystals constitute an attractive alternative to conventional fluorescence thermometers, as they add a long pump interaction length while also being insensitive to strong electrical fields or inert to bio-chemical environments.

Lab-on-a-Chip (LoC) devices combining microfluidic analyte provision with integrated optical analysis are highly desirable for several applications in biological or medical sciences. While the microfluidic approach is already broadly addressed, some work needs to be done regarding the integrated optics, especially provision of highly integrable laser sources. Polymer optical fiber (POF) lasers represent an alignment-free, rugged, and flexible technology platform. Additionally, POFs are intrinsically compatible to polymer microfluidic devices. Home-made Rhodamine B (RB)-doped POFs were characterized with experimental and numerical parameter studies on their lasing potential. High output energies of 1.65 mJ, high slope efficiencies of $56\%$ , and $50\%$ -lifetimes of ≥900 k shots were extracted from RB:POFs. Furthermore, RB:POFs show broad spectral tunability over several tens of nanometers. A route to optimize polymer fiber lasers is revealed, providing functionality for a broad range of LoC devices. Spectral tunability, high efficiencies, and output energies enable a broad field of LoC applications.

With their dipole‐forbidden 4f transitions, lanthanides doped in nanoparticles promise high excited state lifetimes and quantum yields that are required for applications such as composite lasers or nanoscale quantum memories. Quenching at the nanoparticle surface, however, severely reduces the lifetime and quantum yield and requires resource‐consuming experimental optimization that could not be replaced by simulations due to the limitations of existing approaches until now. Here, a versatile approach is presented that fully accounts for spatiotemporal dynamics and reliably predicts the lifetimes and quantum yields of lanthanide nanoparticles. LiYF₄:Pr³⁺nanoparticles are synthesized as a model system, and the lifetimes of a concentration series (≈10 nm, 0.7−1.47 at%) are used to match the model parameters to the experimental conditions. Employing these parameters, the lifetimes and quantum yields of a size series (≈5 at%, 12−21 nm) are predicted with a maximum uncertainty of 12.6%. To demonstrate the potential of the model, a neutral shell is added around the core particles in the model which extends the lifetime by up to 44%. Furthermore, spatiotemporal analysis of single nanoparticles points toward a new type of energy trapping in lanthanide nanoparticles. Consequently, the numerical optimization brings applications such as efficient nanoparticle lasers or quantum memories within reach.

Lanthanide-doped nanothermometers are used to measure temperature through changes in their emission characteristic with sensitivities of up to a few %/K. In contrast to their sensitivity, their spatial resolution, which is of critical importance for various applications, has not been thoroughly studied and optimized. We numerically investigated the improvement in spatial resolution of nanothermometers with a stimulated emission depletion microscopy approach. Fundamental relationships between spatial and temperature resolution were identified by using different beam parameters for the excitation and depletion beams. Our simulations predict contactless temperature measurement below the diffraction limit with temperature resolution of ± 1.25 K . We further studied the influence of sample thickness and position on both temperature and spatial resolution and showed the potential of three-dimensional measurements.

Polymers doped with laser dyes are promising materials for solid state dye lasers. The development of dye doped polymer optical fibers is presented. Furthermore, experimental results from polymer bulk and fiber lasers based on these optical materials are reported.

Lasers emitting in the visible spectral range are of interest for various applications, e.g. in life sciences. Fiberbased setups of such lasers are highly desirable owing to their compactness and alignment-free operation but have only been reported for fluoride fibers or polymer fibers doped with dyes. While fluoride fibers are more difficult to manufacture and to handle in comparison to fused silica fibers, laser-active dyes implemented in a polymer matrix degrade after few hours of laser operation [1, 2]. Multiphonon quenching is the dominating mechanism preventing the usage of rare-earth dopands such as Praesodymium and Samarium in fused silica hosts.