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This dissertation explores the multifaceted roles of rare-earth doped hydroxyapatite in biomedical applications, bridging the gap between luminescence studies and osteogenic potential in the context of bone tissue engineering and regenerative medicine. In the second chapter, we look into the luminescence properties of terbium, cerium, and europium doped hydroxyapatite scaffolds when immersed in simulated body fluid (SBF) over a four-week period. Our comprehensive study reveals a consistent decrease in luminescence emission intensity across all samples, accompanied by a reduction in the concentration of rare-earth ions within the scaffolds, as confirmed by energy dispersive spectroscopy. Furthermore, fluorescence spectroscopy demonstrates the translocation of these ions into the SBF, indicating the scaffolds' partial dissolution over time. The employment of rare-earth ions as luminescence markers offers profound insights into apatite formation mechanisms, presenting significant implications for the development of safer and more durable materials in biomedical applications.Expanding upon the foundational knowledge established in the first and second chapters, the third chapter investigates the osteogenic potential of rare-earth doped hydroxyapatite scaffolds using a murine pre-osteoblastic cell line. This study assesses the effects of ytterbium, terbium, cerium, and europium doping on osteoblast differentiation, gauged by alkaline phosphatase activity and the expression of osteogenic marker genes such as Runx2, OCN, ALP, OPN, and BMP2. Our findings indicate a notable enhancement in differentiation activity with the incorporation of rare-earth elements, with europium and ytterbium doped HAp showing superior performance. Cathodoluminescence spectroscopy further corroborates these results by revealing distinct emission peaks specific to the Eu2+/Eu3+ and Yb2+ ions, underscoring the role of valence state incorporation in augmenting osteoblast differentiation.Collectively, this dissertation contributes expanding the field of biomaterials by elucidating the dual utility of rare-earth doped hydroxyapatite scaffolds in promoting osteogenic differentiation and providing luminescence-based insights into scaffold behavior in physiological environments. By combining the luminescence stability studies with the exploration of osteogenic potential, our research underscores the importance of integrating multifunctional elements into scaffold design to enhance their performance in bone tissue engineering. The insights garnered from both studies not only pave the way for the development of novel biomaterials but also highlight the potential of rare-earth elements as pivotal components in the advancement of regenerative medicine and biomedical engineering.

Down conversion (DC) in rare-earth-doped optical materials is a process of great interest for the possibility of a substantial increase of the efficiency of silicon solar cells. Here we report the structural and photoluminescence properties of co-doped CaF2 phosphors obtained by hydrothermal synthesis. In particular, the DC photoluminescence characteristics for UV (353 nm) excitation of Nd3+/Yb3+ co-doped CaF2 phosphors are discussed, underlining the effects due to the co-doping with Li+. The photoluminescence emission is dominated by the near-infrared (NIR) Yb3+ emission peaked at 975 nm, although the excitation spectrum corresponds to the characteristic peaks associated with Nd3+ excitation at both the UV and visible wavelength ranges. The Nd3+ to Yb3+ energy transfer mechanisms were determined from a detailed analysis of the excitation spectra characteristics of Nd3+ and Nd3+/Yb3+/Li + doped CaF2 phosphors. DC photoluminescence for UV excitation was confirmed by both the analysis of DC quantum yield efficiency and effective quantum yield measurements. In the first case, an efficiency up to 150% was found, while the effective quantum yield measurements, carried out for the UV (DC) and visible (downshift) excitation and NIR photoluminescence emission, give values of 81 ± 10% and 37 ± 5% for excitation with 353 nm and 577 nm light, respectively.

Ideally, any material used should be nontoxic and produced with safe, inexpensive, and energy‐effective processes. In the case of optically active nanoparticles, this is often not the case, as they are frequently composed of hazardous heavy metals and/or produced with methods far from being environmentally friendly. Herein, the preparation of Ag2S‐based nanoparticles via a simple green synthesis route is explored. Aqueous extracts of roasted coffee are used as sources of coordinating molecules. Optimization of the reaction conditions yields dimeric Ag−Ag2S nanoparticles, whose near‐infrared photoluminescence can be switched on via H2O2‐mediated oxidation. This oxidation transforms suitable photoacoustic contrast agents into fluorescence imaging probes. Theoretical calculations further clarify the role of metallic silver in determining the optical properties of Ag2S. Overall, it is demonstrated that nanomaterials with tangible applicative potential can be prepared via cost‐ and energy‐effective synthesis strategies that entail benign, renewable chemicals.

Biomedicine is continuously demanding new luminescent materials to be used as optical probes for the acquisition of high resolution, high contrast and high penetration in vivo images. These materials, in combination with advanced techniques, could constitute the first step towards new diagnosis and therapy tools. In this work, we report on the synthesis of long lifetime rare-earth-doped fluoride nanoparticles by adopting different strategies: core/shell and dopant engineering. The here developed nanoparticles show intense infrared emission in the second biological window with a long luminescence lifetime close to 1 millisecond. These two properties make the here presented nanoparticles excellent candidates for time-gated infrared optical bioimaging. Indeed, their potential application as optical imaging contrast agents for autofluorescence-free in vivo small animal imaging has been demonstrated, allowing high contrast real-time tracking of gastrointestinal absorption of nanoparticles and transcranial imaging of intracerebrally injected nanoparticles in the murine brain, This work was supported in part by the grants from the Fundamental Research Funds for the Central Universities, China (HIT. BRETIV.201503 and AUGA5710052614) and the National Natural Science Foundation of China (51672061). We thank Dr Lina Wu at the Fourth Hospital of Harbin Medical University for her kind help with the MTT assay, and Dr Tymish Y. Ohulchanskyy at Shenzhen University for his kind help with the fluorescence lifetime measurement. The work was also supported by the Ministerio de Economia y Competitividad of Spain (grant MAT2016-75362-C3-1-R). Jie Hu acknowledges the scholarship from the China Scholarship Council (No. 201506650003). Dirk H. Ortgies is grateful to the Spanish Ministry of Economy and Competitiveness for a Juan de la Cierva scholarship (No. FJCI-2014-21101) and the Spanish Institute of Health (ISCIII) for a Sara Borell Fellowship (No. CD17/00210)

A sensor based on luminescence has been prepared depositing the luminescent complex platinum tetrakis pentrafluorophenyporphine (PtTFPP) onto a plastic-clad silica (PCS) optical fiber. The sensing film is constructed in terms of Layer-by-Layer method. A LED centered at 400nm was used to interrogate the sensor in a reflection configuration, registering a luminescent signal from the sensing material located at 648nm. The transduction principle is based on the quenching suffered by PtTFPP as the oxygen (O2) concentration increases. The sensor was characterized for O2 concentrations from 0% to 75%, showing a linear Stern–Volmer relationship (R2 = 0.9962).

Most commercially available optical oxygen sensors target the measuring range of 300 to 2 mu mol L-1. However these are not suitable for investigating the nanomolar range which is relevant for many important environmental situations. We therefore developed a miniaturized phase fluorimeter based measurement system called the LUMOS (Luminescence Measuring Oxygen Sensor). It consists of a readout device and specialized "sensing chemistry" that relies on commercially available components. The sensor material is based on palladium(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin embedded in a Hyflon AD 60 polymer matrix and has a K-SV of 6.25 x 10(-3) ppmv(-1). The applicable measurement range is from 1000 nM down to a detection limit of 0.5 nM. A second sensor material based on the platinum(II) analogue of the porphyrin is spectrally compatible with the readout device and has a measurement range of 20 mu M down to 10 nM. The LUMOS device is a dedicated system optimized for a high signal to noise ratio, but in principle any phase flourimeter can be adapted to act as a readout device for the highly sensitive and robust sensing chemistry. Vise versa, the LUMOS fluorimeter can be used for read out of less sensitive optical oxygen sensors based on the same or similar indicator dyes, for example for monitoring oxygen at physiological conditions. The presented sensor system exhibits lower noise, higher resolution and higher sensitivity than the electrochemical STOX sensor previously used to measure nanomolar oxygen concentrations. Oxygen contamination in common sample containers has been investigated and microbial or enzymatic oxygen consumption at nanomolar concentrations is presented. Most commercially available optical oxygen sensors target the measuring range of 300 to 2 μmol L-1. However these are not suitable for investigating the nanomolar range which is relevant for many important environmental situations. We therefore developed a miniaturized phase fluorimeter based measurement system called the LUMOS (Luminescence Measuring Oxygen Sensor). It consists of a readout device and specialized “sensing chemistry” that relies on commercially available components. The sensor material is based on palladium(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin embedded in a Hyflon AD 60 polymer matrix and has a KSV of 6.25 x 10-3 ppmv-1. The applicable measurement range is from 1000 nM down to a detection limit of 0.5 nM. A second sensor material based on the platinum(II) analogue of the porphyrin is spectrally compatible with the readout device and has a measurement range of 20 μM down to 10 nM. The LUMOS device is a dedicated system optimized for a high signal to noise ratio, but in principle any phase flourimeter can be adapted to act as a readout device for the highly sensitive and robust sensing chemistry. Vise versa, the LUMOS fluorimeter can be used for read out of less sensitive optical oxygen sensors based on the same or similar indicator dyes, for example for monitoring oxygen at physiological conditions. The presented sensor system exhibits lower noise, higher resolution and higher sensitivity than the electrochemical STOX sensor previously used to measure nanomolar oxygen concentrations. Oxygen contamination in common sample containers has been investigated and microbial or enzymatic oxygen consumption at nanomolar concentrations is presented.

The nanoparticles of hydroxiapatite and fluorapatite doped with Er/Yb and Tm/Yb were synthesized and characterized by FTIR, XRD, SEM and TEM methods. The results of up-conversion luminescence studies were presented for the samples as prepared, annealed at 500°C and at 900-1000 °C. At annealing above 800°C the ceramic state was formed. It is shown that fluorapatite host is more appropriate than hydroxiapatite host for rare ions luminescence and up-conversion processes. The post preparing annealing of nanarticles significantly enhanced the luminescence intensity. The Tm/Yb doped fluorapatite shows intense up-conversion luminescence in 790-800 nm spectral region and is potentially useful for biomedical applications.