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Combining treatment and diagnosis, called theranostics, which is achieved within single nanoparticle is an ultimate goal of many studies. Herein, we developed a new nanotheranostic agent − Nd3+-sensitized upconversion nanoparticles core for dual modal imaging (i.e., upconversion luminescence imaging and magnetic resonance imaging) and antimony nanoshell for photothermal therapy (PTT). The core-shell-shell upconversion nanoparticles (NaYF4:Yb,Er@NaYF4:Yb,Nd@NaGdF4:Nd, named as UCNP) were firstly synthesized using thermal decomposition method and then were coated by antimony shell over the surface of UCNP using simple cost and time effective new method. Furthermore, the surface of UCNP@Sb nanostructures was modified with DSPE-PEG in order to enhance the water solubility and biocompatibility. The final nanotheranostic agent, named as UCNP@Sb-PEG, exhibits very low toxicity, good biocompatibility, very good photothermal therapeutic effect, and efficient upconversion luminescence (UCL) imaging of HeLa cells under only one laser (808 nm) irradiation. The antimony shell is quenching the upconversion emission in pristine nanotheranostic agent, but interestingly, the UCL intensity of the agent recovers progressively under 808 nm laser irradiation due to light induced degradability of antimony shell. Besides, high longitudinal relaxivity (r1) obtained from the experiment approves excellent potential of the nanotheranostic agent for T1-weighted magnetic resonance imaging application.

Luminescence thermometry (LT) is a remote technique of temperature monitoring, which shows immense potential and has become very popular among researchers in recent years. LT can be realized by several different measurement methods, but one of the most recently proposed and least studied relies on a single-band ratiometric (SBR) approach. In the SBR approach, temperature is achieved from a single emission band being photoinduced by two different excitation conditions, i.e. ground (GSA) and excitated (ESA) state absorption. However, the intensity of emission resulting from by ESA excitation is dependent on many factors such as host material properties, type and concentration of optically active dopant ions, surface effects and others, and thus in-depth understanding of photophysical processes is indispesible to enable intentional development of novel highly sensitive luminescent thermometer working based on SBR principle. In these studies, the impact of host matrix and interionic interactions occurring through cross-relaxation on the thermometric properties of a single-band ratiometric thermometer based on nanosized NaYF4 and NaGdF4 fluorides doped with Eu3+ ions are investigated and discussed. The maximum relative temperature sensitivity was equal SR=16.9%/K at 163 K for the NaGdF4:50%Eu3+ nanocrystals and was close to 1%/K over the entire higher temperature range analyzed.

Luminescent nanothermometry (LNT) based on temperature-dependent emission intensity of transition metals (TM) is a promising new direction to enhance the performance and implement LNT in many fields of science and technology. However, insightfully understanding and analysis of the luminescence thermal quenching mechanisms in this type of compounds is required. In this work, we study temperature sensitivity (S) modified by crystal field engineering in Gd3Al5-xGaxO12:Cr3+, Nd3+ TM:LNTs. Substituting Al3+ ions in the host matrix by Ga3+ ones, caused gradual decline of crystal field strength from Dq/B = 2.69 for Gd3Al5O12:Cr3+, Nd3+ to the Dq/B = 2.18 for Gd3Ga5O12:Cr3+, Nd3+. In consequence, improvement of relative sensitivity was observed. Two temperature dependent parameters were taken into considerations as potential temperature measure, i.e. luminescence intensity ratios of 4T2 → 4A2 (Cr3+) to 4F3/2 → 4I9/2 (Nd3+) and 2E → 4A2 (Cr3+) to 4T2 → 4A2 (Cr3+). The proposed method, based on crystal field strength engineering, improved the relative temperature sensitivity by over 1.37%/°C for −1 Dq/B change in crystal field strength, from initial 1.2–1.9%/°C.

Quantitative comparison of emission intensity between lanthanide doped upconverting (UC) nanoparticles is critical to evaluate the impact of host matrix and nanocrystal size, active- and passive- dopants, core-shell chemical architecture, surface biofunctionalization and others, which are typically a subjects to optimization. While relative luminescence intensity has been commonly used for that purpose, quantum yield (QY) is another accurate measure, because here, number of UC emission photons is normalized to the number of photons being absorbed. However, this type of measurements have been hindered by limited availibility of commercial instrumentation. Here we show a novel, simple and affordable UCQY setup design and versatilely characterize its performance using Yb3+ and Ho3+ co-doped colloidal NaYF4 nanoparticles dispersed in chloroform. The UCQY showed a liner dependence on excitation intensity, and reached up to 0.41% and 0.25% for the 2% Ho3+, 20% Yb3+ and 0.1% Ho3+, 20% Yb3+ materials, respectively. Interestingly, the UCQY values depend on the selection of reference material and concentration of NPs. In particular, the un-doped reference NPs of the same diameter as the sample NPs show higher UCQY values than the ones obtained for the pure solvent. Moreover, UCQY depend on the concentration of the NPs. These two effects were related to the scattering of photoexcitation beam in the sample and reference materials. Additionally, no saturation of power dependent UC was seen up to ~270 W/cm2 excitation intensities, which we relate to the photoexcitation methodology. In opposite to the Continuous Wave photoexcitation, we used Pulse Width Modulation of photoexcitation intensity, and confirm such behavior with a simple, time – resolved differential rate equations based model. These findings and reliable UCQY instruments are important to quantitatively compare and further optimize the performance of UCNPs.

In this work, properties of the near infrared absorbing and near infrared emitting Er3+ and Nd3+ co-doped LaPO4 nanocrystals luminescent thermometer were investigated by exploiting luminescence spectra ratiometric and luminescence lifetime. The unique configuration of the energy levels of Nd3+ and Er3+ ions and the energy transfer between them requires temperature dependent phonon assistance. Since, the probability of this process is dependent on the distance between interacting ions, the thermometric parameters of luminescent thermometers were investigated as a function of Er3+ dopant concentration. Strong susceptibility of its probability to temperature changes enables to quantify temperature with relative sensitivity as high as SR = 1.15%/K for LaPO4:1%Nd3+, 20%Er3+ nanocrystals in the ratiometric approach and SR = 2.3%/K at 600 K for LaPO4:1%Nd3+, 5%Er3+ in the luminescence lifetime based mode. The obtained results confirm the high applicative potential of this phosphor for remote temperature measurements.

One of the newest approaches to ratiometric luminescence thermometry, namely, the single band ratiometric (SBR) approach, that involves excited state absorption, has been intensively investigated in recent years due to its unique features. The development of the highly sensitive luminescent temperature probe based on this approach is possible only when the physical processes and material parameter of the phosphors that affects the probability of the excited state absorption will be determined. Therefore, in this work, for the first time, the influence of phosphor size and the role of surface quenching processes on the sensitivity of this type of luminescent thermometers are investigated and discussed. It has been shown that surface related depopulation processes of the intermediate 4I11/2 energy levels strongly affect the intensity of the 4F3/2→4IJ emission excited by excited state absorption. It leads to a reduction of the sensitivity of this type of luminescent thermometers and a narrowing of its usable temperature range. As a consequence, it has been shown that the maximum relative sensitivity of YAG:Nd-based thermometer changes as follows 2.38 %/oC, 8.46 %/oC and 9.51 %/oC for a phosphor in the form of nanocrystals, microcrystals and ceramics, respectively.

Light-based diagnostics and therapy have become indispensable tools in the field of cancer nanomedicine. Various optical imaging modalities with tomographic capability have been developed to visualize cellular and organismic distributions of molecules. Microscopic pharmacokinetics and the tumor-targeting efficacy of nanoscale effectors can now be precisely evaluated. Moreover, phototherapy using intense laser light has been widely used for treating cancers. Using light-active nanoscale effectors, photothermal and photodynamic therapies on superficial tumors can be achieved with low-illumination lasers. Consequently, for the next generation of photo-medical techniques, the use of near infrared (NIR) excitation sources on NIR-activatable nanoparticles may offer deeper light penetration owing to less extensive scattering and absorption by endogenous chromophores in the NIR spectral region. Therefore, treatments and biodetection within higher tissue volumes and with less side effects (e.g. overheating) may be successfully implemented. This comprehensive review covers the state-of-the-art technologies on (a) advanced laser light sources appropriate for deep tissue theranostics, (b) types of laser interactions with pure-NIR and NIR-upconverting nanomaterials, (c) current development of NIR and multi-photon nanoparticles, (d) application fields of NIR nanomaterials in cancer theranostics, and (e) nanotoxicology of NIR nanoscale effectors for cancer treatment.

Up-converting properties of LiLaP 4 O 12 :1%Tm 3+ , 50%Yb 3+ , x% Eu 3+ nanocrystals were investigated upon 975 nm excitation. It was shown that their emission color can be tuned from blue to orange via changing Eu 3+ concentration from 10% to 49%. The potential suitability of these nano-phosphors for non-contact temperature sensing was investigated. Thermal changes of luminescence intensity ratio of 1 D 2 → 3 F 4 and 1 G 4 → 3 F 4 emission bands of Tm 3+ ions were strongly affected by Eu 3+ concentration owing to increasing efficiency of distance-dependent Tm 3+ →Eu 3+ energy transfer. The sensitivity of such luminescence thermometer was varying from 0.1%/°C to 1.9%/°C in response to varying Eu 3+ concentration from 49 down to 10%.

The concentration dependent up-conversion luminescence of 0.1; 0.2; 0.5; 1; 1.5; 2; 3; 4 and 5% Ho3+ and 20% Yb3+ co-doped β-NaYF4 colloidal nanocrystals have been studied. The obtained nanocrystals were homogenous in size and shape, as well as the crystallographic structure was pure. The absorption spectra, upconversion lifetimes, up-conversion emission and Quantum Yield power dependence have been measured to estimate the optimum doping concentration of Ho3+ ions. The experimental results were supported by the calculations based on Judd-Ofelt theory, in order to quantify the oscillator strengths in absorption and luminescence, excited-state radiative lifetimes, energy-transfer probabilities, and to estimate the quantum efficiencies of this interesting material. We have observed evident trend in rise- and luminescence decay profiles with rising Ho3+ activator concentration, and the 1–2% Ho3+ ions doping was found to be the most efficient nanophosphors.

Transition metal d-f emission based thermometry has recently proven to be an order of magnitude more sensitive than thermometers based on conventional f-f transitions in rare-earth ions. Little is known however about the susceptibility of these materials to nanoscale parameters, such as size or surface-to-volume ratio. Here we study the impact of nanocrystallite size on luminescent properties as well thermometry capabilities of CrNd co-doped LiLaP4O12 phosphors. In particular, we show that absolute emission intensity decreases (∼ 0.81%/nm), emission band position blue shifts (Δl ∼ −0.066 nmwave length/nmgrain size), temperature sensing range narrows (from 300 to 600 K at 240 nm down to 300–420 K at 20 nm), temperature sensitivity rises up (from 1%/K to ∼5%/K) and temperature resolution drops (from ∼0.3 °C down to 0.05 °C) gradually, when the size of NCs decreases from 240 down to 20 nm, respectively. As a consequence, proper design of host and dopants, enables finding optimal materials for many thermometry applications.

Simple and effective ways to circumvent limited luminescence efficiency of up-converting nanoparticles (UCNPs) are sought. One of the methods relays on distorting the crystallographic structure of host material by co-doping the nanocrystals with optically inactive co-dopants. Here we study the influence of K+ doping and surface passivation on the up-converting properties of the α-NaYF4 nanocrystals co-doped with 20% Yb3+ and 0.1 or 2% Tm3+. The intentionally chosen concentrations of K+ ions, which were meant to replaced sodium ions were fixed to 0, 5, 10, 20 to 30%. Potassium ions modified the spectroscopic properties of both core and core–shell NPs, but the differences were noticed between samples doped with 0.1% Tm3+ and 2% Tm3+ ions. Replacement of sodium by potassium ions decreased up-conversion luminescence intensity as well as shortened thulium excited states lifetimes in the samples doped with 0.1% Tm3+, while the opposite behavior was found in the samples co-doped with higher 2% thulium concentration.

The synthesis and luminescent properties of water colloidal solution of LiNdP4O12 nanocrystals were presented together with demonstrations of their suitability for bio-imaging, remote nano-thermometry and hyperthermal therapy bio-applications. Due to efficient and photostable luminescence at 860 nm under ~808 nm excitation, NPs luminescence was measured in chicken breast at down to 30 mm depths. Moreover temperature dependent spectroscopic features were used in order to remotely measure the temperature of the local environment. Simultaneously, the most heavily Nd3+ doped NCs demonstrated intentional heating – under 1.5 W of excitation power at 800 nm, local 60 K photo-induced temperature rise was observed. The experimental confirmation of bioimaging of LiNdP4O12 nanoparticles in HEK was presented.

To increase luminescence efficiency, the substitution of matrix ions with ion of alternative size and valence has been used to create lattice distortions and disrupt the processes responsible for luminescence quenching. Therefore, luminescent properties of cubic NaYF 4 :Yb 3+ /Tm 3+ nanocrystals co-doped with Ca 2+ ions have been studied. The general increase in the luminescence intensity as well as in thulium excited states lifetimes have been observed upon Ca 2+ doping. The optimal calcium ions concentration has been found equal to 5% in the case of samples doped with 0.1% Tm 3+ . The most efficient UC luminescence in the case of 2% Tm 3+ doped samples has been observed for 10% Ca 2+ doped sample. Additionally, the impact of intentional substitution of either Na + or Y 3+ ions by Ca 2+ ions in NaYF 4 matrix has been compared. Similar modulation effects have been observed for both doping methods.

The possibility to design and intentionally tune the luminescent properties of phosphors, e.g. their emission colour, quantum yield and kinetic behavior, is of fundamental significance and a challenge for numerous applications. Usually, to obtain multicolour emission, multiple nanomaterials with different co-dopants combinations, sizes or chemical architectures are synthesized and characterized. Of special interest would be those materials, where on-demand and in-situ modifications of multicolour emission can be obtained by changing the external stimulus, such as magnetic field, temperature, excitation intensity or pulse width. Here we synthesize and evaluate luminescent NaYF4 nanoparticles doped Yb3+/Ho3+, whose red and green emission colour is modulated by variable concentration of Ce3+ admixture, excitation pulse duration and temperature. In the first scenario (Yb3+/Ho3+ only doping), such materials exhibit strong and stable green upconversion emission. Upon Ce3+ co-doping, the red to green ratio (RGR) changed from 0,43 (for pristine dopants) to 4,23 (for 15%Ce3+ co-doped samples). Moreover, the measurement performed with excitation pulse width modulation (PWM) enabled to increase contribution of red emission in-situ. For short excitation pulses, the green emission was observed, while for longer pulses the red emission started to dominate. Finally, the energy transfer in this tri-doped system demonstrated to be susceptible to external temperature as well, with relative thermal sensitivity of 0,8%/K in biological range for 5%Ce3+ doped sample. Detailed spectroscopic analysis including temperature dependent emission spectra, rise times and emission kinetics allow us to understand and propose the possible energy transfer mechanisms in this system.

The most commonly applied luminescent thermometry (LTs) approach, which are based on the luminescence intensity ratio (LIR), requires integration of the analyzed emission bands. This analysis is often cumbersome and technically challenging due to spectral overlap and vicinity of the two emission bands. These limitations can be overcome by a new, single emission band ratiometric (SBR) approach which involves excitation through thermally induced excited state absorption (ESA) and ground state absorption (GSA). What is more, the frequent problem of low intensity of one of the radiative transitions, which are analyzed in conventional luminescent thermometry, is overcome owing to the involving of the SBR approach. Due to the opposable behavior of the emission intensity with temperature changes upon these two excitation schemes, improved thermal sensitivity can be achieved. In this work, the suitability of Nd3+-doped oxyfluorotellurite (65-x)TeO2–20ZnF2–12PbO–3Nb2O5–xNd2O3 (x = 0.1, 1, 2, 5 and 10) glasses (TZPN) was analyzed for SBR-based luminescent thermometry. To excite Nd3+ ions, the 808 nm and 1060 nm wavelengths, which are related to GSA and ESA, respectively, were involved. In the biological temperature range the relative sensitivity reached SR = 2.95%/°C. The highest value of SR = 6.15%/°C was obtained at low temperature range for the 10%Nd3+:TZPN glass LT and decreased below 1%/°C only at temperatures above 200 °C.

Luminescent thermometry is rapidly growing experimental technique of thermal sensing, which provides the temperature detection in real time and contactless way. To address existing challenges of accurate temperature measurement, we developed and investigated new Sr2CeO4 nanocrystalline inorganic dual luminescence temperature sensors and optimized their temperature sensitivity and temperature operating range by introducing lanthanide co-dopants (Ln3+ = Ho3+, Yb3+, Nd3+, Sm3+) to luminescent Ce3+ ions in . Both, spectral and temporal temperature susceptibility of newly developed sensors, have been demonstrated and evaluated. In general, lanthanide doping leads to the shortening of luminescent decay time owing to enhanced thermal quenching rate. Among all Ln3+ ions studied here, the employment of Yb3+ ions provides the widest temperature range and highest relative temperature sensitivities, both, based on luminescence lifetime and ratiometric luminescence operating principles (2.80%/oC at −45 °C). However, for temperatures above 50 °C, the Sr2CeO 4 :Ho3+ ratiometric luminescent thermometer is proven to perform better, which exhibited relative sensitivities above 1%/oC. The advantage of using Ho3+ and Sm3+ doped Sr2CeO4 nanocrystalline luminescent thermometers is the fact, their visible emission colour is responsive to temperature changes, which enables naked-eye qualitative evaluation as well. It is worth noticing, to the best of our knowledge this works reports the highest relative sensitivity for Ln4+ based luminescent thermometers.

Luminescence decays of metastable Nd 3+ : 4 F 3/2 level were measured and studied in wide of 10–300 K temperature range and compared with the radiative lifetimes derived from standard Judd–Ofelt theory. Nearly resonant cross-relaxation was found to non-radiatively depopulate the metastable level already in 10 K, whereas above 50 K increased reabsorption of radiation and thermalization of higher Stark component of the 4 F 3/2 level occur, which resulted in the Boltzmann population of this metastable Nd 3+ level and anomalous increase of luminescence decays with temperature increment.

Optical imaging plays an important role in biomedical research being extremely useful for early detection, screening and image-guided therapy. Lanthanide-doped up-converting nanoparticles were ideally suited for bioimaging because they could be excited in near infrared (NIR) and emit in NIR or visible (VIS). Here, we compared lanthanide doped up-converting NaYF 4 and organic fluorophores for application in deep-tissue imaging. For that purpose - tissue phantoms mimicking the natural properties of light scattering by living tissues were prepared. The studies allowed to quantitatively compare optical resolution of different fluorescent compounds, revealing that the NIR photoexcitation was favorable over conventional UV photoexcitation.

This contribution presents two simple and cost-effective routes for the low-temperature and large-scale production of pure and Eu-doped Y 3 Al 5 O 12 (yttrium aluminum garnet YAG) nanopowders. The proposed methodologies combine a mechanically assisted metathesis reaction or coprecipitation from solution followed by crystallization of the obtained precursors from molten sodium nitrate/nitrite. Both procedures allow obtaining pure and/or doped YAG nanopowders at remarkably low temperatures, i.e. already at 350 °C although firing at 500 °C is needed in order to get single phase and fully crystalline materials. As-obtained samples were characterized by XRD, TEM, Raman, IR and luminescence methods. These methods showed that the mean crystallite size is near 23–31 and 51 nm, when crystallization is performed from the amorphous precursor obtained by a mechanically assisted metathesis reaction and coprecipitation, respectively. Raman and IR spectra indicated better crystallinity of the powders prepared at 500 °C. The emission study showed that the intensity ratio between hypersensitive 5 D 0 → 7 F 2 and magnetic-dipole 5 D 0 → 7 F 1 transitions of Eu 3+ is significantly larger than expected for well-crystallized YAG. Origin of this behavior is discussed.

þ co-doping Up-conversion luminescence Cubic NaYF4 Nanocrystals abstract The impact of Li þ doping on luminescence and structural properties of cubic NaYF4:Yb 3 þ /Tm 3 þ colloidal nanocrystals was studied. The Yb 3 þ /Tm 3 þ co-doped samples demonstrated significant red to blue emission ratio changes and high concentration quenching. By substituting Na þ with smaller Li þ ions within NaYF4 lattice, we expected to induce distortions in order to prevent the concentration quenching process, which is responsible for decrease of the luminescence intensity. The results indicated that the substitution of sodium ions by Li þ did not enhance Tm 3 þ up-conversion emission significantly in α- NaYF4:Yb 3 þ /Tm 3 þ . However, the influence of lithium ions on luminescence was not entirely the same in the case of 2% Tm 3 þ and 0.1% Tm 3 þ doped samples. The slight up-conversion intensity enhancement in the case of samples doped with 2% Tm 3 þ could result from the increase in the crystallites size and changes in the surface to volume ratio. The observed increase in lattice parameter and thus the increased distance between thulium ions in the lattice might also result in breaking apart of pairs responsible for cross-relaxation processes. Interestingly, in the 0.1% Tm 3 þ co-doped samples, initial luminescence intensity decrease followed by increase correlated with Li þ substitution was observed. Due to the existence of two different sites for incorporation of lithium ions into the host lattice, the changes in lattice parameters and resulting optical properties are not straightforward functions of variable amount of Li þ .

The Tb 3+ up-conversion phosphors are promising for biological applications due to their long luminescence lifetime and their spectral fingerprint being different from commonly known materials doped with Yb 3+ /Er 3+ and Yb 3+ /Tm 3+ . The concentration dependent up-conversion emission of terbium ions has been studied in cubic NaYF 4 colloidal nanocrystals doped with terbium activators and ytterbium sensitizer. Further thulium ions co-doping allowed five-fold enhancing of the up-conversion emission intensity from the 5 D 4 terbium level. A versatile optimization of Tb 3+ , Yb 3+ and Tm 3+ concentrations has been performed by means of luminescence spectra and lifetimes as well as power dependence studies. The up-conversion mechanisms have been proposed—cooperative energy transfer (CET) and mixed CET and energy transfer up-conversion (APTE) for Yb 3+ /Tb 3+ and Yb 3+ /Tb 3+ /Tm 3+ doped materials respectively.

Luminescence spectra, power dependence and luminescence lifetimes were measured and studied in pure cubic phase NaYF 4 :20%Yb 3+ , x %Tm 3+ (where x = 0.1%, 0.2%, 0.5%, 1% and 2%) nanocolloidal phosphors synthesized by thermal decomposition. Increasing concentration of Tm 3+ ions led to decrease of luminescence intensity, increase in the slopes of power dependence as well as to the decrease in the luminescence decay- and rise-times, helping to resolve the mechanisms of up-conversion and concentration quenching.

Nanosized CaAl 2 O 4 powders doped with Eu 3+ and charge compensated with Na + co-doping were synthesized with modified Pechini's method. The structural properties of the powders calcined at 900–1100 °C where characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The grains with monoclinic structure formed quite large and aggregated crystallites with irregular shapes and sizes in the range of 100–500 nm. The photoluminescent properties of the phosphores co-doped with different Eu 3+ ions concentration (0.5–5 mol%) were investigated by excitation and emission spectroscopy at room and low (77 K) temperatures. The effect of charge compensation on luminescence properties was noticed. To explain these differences a detailed analysis of luminescence spectra by the Judd–Ofelt theory has been performed.

The intense anti-Stokes white emission of Li(K)P4O12 crystals was observed in vacuum under 808 nm excitation. Influence of optical pumping power and ambient pressure on up-conversion properties have been investigated. It was found that intense white anti-Stokes white emission occurred at vacuum atmosphere. Its origin has been discussed in terms of Nd2+-charge transfer luminescence occurring at the limited thermal conversion of irradiated crystals in vacuum.

Synthesis, crystal structure, morphology and optical properties of three various NaYF 4 nanoparticle systems co-doped with Tm 3+ and Yb 3+ ions have been investigated. Characterization of ultrasmall (size ∼8 nm), small (∼25 nm) NaYF 4 :2%Tm 3+ , 20%Yb 3+ nanoparticles and core–shell structures (NaYF 4 :20%Yb 3+ –NaGdF 4 :2%Tm 3+ ) synthesized according to two different protocols is presented. We have found that the up-conversion luminescence is strongly influenced by the nanoparticle size, internal structure and spatial distribution of active Tm 3+ ions. Further spectroscopic studies revealed significant fluorescence rise and decay time lengthening of the 1 G 4 energy level of Tm 3+ ions in NaYF 4 :20%Yb 3+ –NaGdF 4 :2%Tm 3+ core–shell nanoparticles. The formation of the core–shell structures was proven indirectly through the average crystalline size increase between the bare core and core–shell nanoparticles, the observed changes in EDX composition as well as variation of Tm 3+ ions luminescence properties.

Summary Due to exceptional photo-physical properties, up-converting nanoparticles (UCNPs) are promising and advantageous alternative to conventional fluorescent labels used in many bio-medical applications. The first part of this review aims at presenting these properties as well as the current state-of-the-art in the up-conversion enhancement, NPs surface functionalization and bioconjugation. In the second part of the paper, the applications of UCNPs and currently available detection instrumentation are discussed in the view of the distinctive properties of these markers. Because the growing widespread use of the biofunctionalized NPs, scarce instrumentation for up-conversion detection is reviewed. Finally, the challenges and future perspectives of the UCNPs are discussed.