Artur Bednarkiewicz

Neodymium(III) doped fluoride nanoparticles as non-contact optical temperature sensors

We report that non-contact optical temperature sensing can be achieved with the use of heavily Nd(3+) doped NaYF(4) nanoparticles. The temperature evaluation can be realized either by monitoring the absolute luminescence intensity or by measuring the intensity ratio of the two Stark components of the (4)F(3/2) multiplet in the Nd(3+) ions.

White emission of lithium ytterbium tetraphosphate nanocrystals.

An efficient anti-Stokes white broadband emission induced by 976 nm laser diode in lithium ytterbium tetraphosphate (LiYbP4O12) nanocrystals was investigated. The emission occurs at room temperature and atmospheric pressure. Its intensity demonstrates an evident threshold dependence on the temperature and excitation density characteristic to avalanche process. The white emission is accompanied by very efficient photoconductivity characterized by microampere photocurrent which increases with the fourth order of applied incident light power (~P4). We show that this emission is critically dependent on temperature and increases significantly in vacuum. It is concluded that the anti-Stokes white emission is associated with theYb3+- CT luminescence.

Power dependence of luminescence of Tb3+ -doped KYb(WO4)2 crystal

Abstract The effect of excitation intensity on luminescence properties of Tb3+-doped KYb(WO4)2 crystal is reported. In particular, emissions following the Stokes and anti-Stokes excitations were investigated. It was found that, in addition to the Tb3+ luminescence, an intense Yb3+ luminescence at room temperature was observed after a direct excitation of Tb3+ ions in spite of the fact that both ions are far off-resonance. The intensities of Tb3+ and Yb3+ luminescences were dependent on the excitation power and changed by a sublinear function (slope

Emission properties of nanostructured Eu3+ doped zinc aluminate spinels

Abstract The preparation of nanostructured ZnAl2O4 spinel powders doped with Eu3+ ions obtained by a hydrothermal method is described. XRD analyses demonstrated that the powders were single-phase spinel nanopowders with high crystallite dispersion. The averaged spinel particle size was determined to be 6 nm as prepared and it increased up to 8 nm for calcination at 500°C. The emission spectra of Eu3+ ions measured for the samples calcinated at 500°C demonstrated inhomogeneous shapes characteristic for disordered material which after heating at 1500°C changed shape into an ordered shape characteristic of the crystalline form.

Neodymium-doped nanoparticles for infrared fluorescence bioimaging: The role of the host

The spectroscopic properties of different infrared-emitting neodymium-doped nanoparticles (LaF3:Nd3+, SrF2:Nd3+, NaGdF4: Nd3+, NaYF4: Nd3+, KYF4: Nd3+, GdVO4: Nd3+, and Nd:YAG) have been systematically analyzed. A comparison of the spectral shapes of both emission and absorption spectra is presented, from which the relevant role played by the host matrix is evidenced. The lack of a “universal” optimum system for infrared bioimaging is discussed, as the specific bioimaging application and the experimental setup for infrared imaging determine the neodymium-doped nanoparticle to be preferentially used in each case.

Cooperative processes in KYb(WO4)2 crystal doped with Eu3+ and Tb3+ ions

Abstract The cooperative processes occurring between Eu 3+ (Tb 3+ ) and Yb 3+ ions in the KYb(WO 4 ) 2 crystal are reported. In this crystal the excited state of Yb 3+ ( 2 F 5/2 ) is far of resonance with Eu 3+ and Tb 3+ ions. In particular, the emission processes following the Stokes excitation and the anti-Stokes excitation, e.g. down-conversion and up-conversion, respectively, were investigated. It was found that the Yb 3+ emission was fairly intense in spite of the fact that the cross-relaxation is of the non-resonant type. The up-conversion emission of Eu 3+ (red) and Tb 3+ (green) ions following a direct excitation of Yb 3+ ions was observed at room temperature. The dependence of emission intensity on incident laser power was measured. It was found that the efficiency of Stokes emissions is described by the slope of allometric curve less than 1 whereas for the anti-Stokes emission (up-conversion) the slope was around 2. The mechanisms of down- and up-conversion processes are briefly discussed.

A new generation of highly sensitive luminescent thermometers operating in the optical window of biological tissues

A new type of luminescent thermometer based on highly temperature dependent d–d Cr3+ transitions related to barely temperature dependent f–f Nd3+ transitions is reported for the first time, showing exceptionally high sensitivity and shifting current paradigms behind the physics and chemistry of luminescent nanothermometers. The highest sensitivity in the physiological temperature range was found for LiLaP4O12:1%Cr,10%Nd and reached 4.89%/°C – three times, up to over one order of magnitude higher than most luminescent thermometers reported to date. Moreover, the brightness of such probes based on Cr ions was around one order of magnitude higher than the Stokes Nd emission. Even higher sensitivities, up to 30%/°C, were found above 200 °C, indicating the importance of a rational approach to the design of chemical composition and smart involvement of photophysical processes, to significantly enhance the properties of luminescent thermometers. The thermal dependence of the luminescence intensity ratio from the two ions was investigated for different Cr3+ and Nd3+ ion concentrations, which actually had no severe impact, either on the LIR or on the sensitivity of such luminescent thermometers.

Giant enhancement of upconversion in ultra-small Er3+/Yb3+:NaYF4 nanoparticles via laser annealing

Most of the synthesis routes of lanthanide-doped phosphors involve thermal processing which results in nanocrystallite growth, stabilization of the crystal structure and augmentation of luminescence intensity. It is of great interest to be able to transform the sample in a spatially localized manner, which may lead to many applications like 2D and 3D data storage, anti-counterfeiting protection, novel design bio-sensors and, potentially, to fabrication of metamaterials, 3D photonic crystals or plasmonic devices. Here we demonstrate irreversible spatially confined infrared-laser-induced annealing (LIA) achieved in a thin layer of dried colloidal solution of ultra-small ∼8 nm NaYF₄ nanocrystals (NCs) co-doped with 2% Er³⁺ and 20% Yb³⁺ ions under a localized tightly focused beam from a continuous wave 976 nm medium power laser diode excitation. The LIA results from self-heating due to non-radiative relaxation accompanying the NIR laser energy upconversion in lanthanide ions. We notice that localized LIA appears at optical power densities as low as 15.5 kW cm⁻² (∼354 ± 29 mW) threshold in spots of 54 ± 3 µm diameter obtained with a 10 × microscope objective. In the course of detailed studies, a complete recrystallization to different phases and giant 2-3 order enhancement in luminescence yield is found. Our results are highly encouraging and let us conclude that the upconverting ultra-small lanthanide-doped nanophosphors are particularly promising for direct laser writing applications.

Laser-induced hot emission in Nd3+/Yb3+: YAG nanocrystallite ceramics

It was found that under intense CW excitation of Yb3+/Nd3+ : YAG nanocrystallite ceramics by 976 nm laser diode (pumping directly Yb3+ ion), the visible hot emission occurred. Its intensity exhibited long emission build-up times (of an order of seconds) after turning on the excitation source. The intensities of hot emission of Nd3+ ion increased with the excitation power demonstrating the dependence IN, with the order parameter N demonstrating a linear dependence on the energy distance ΔE = Eemhot−E(4F3/2).

Laser action in LaAlO3:Nd3+ single crystal

The spectral and laser properties of Nd3+ doped (1wt%) LaAlO3 single crystal are presented. The energy levels of the Nd3+ ion in the LaAlO3 matrix were assigned. The Judd–Ofelt parameters Ω2=1.346, Ω4=4.490, and Ω6=5.168 (all ×10−20cm−2) were evaluated. The absorption σabs and emission σemi cross sections at the respective pumping and emission wavelengths were calculated to be σabs(789.7nm)=2.42×10−20cm2, σemi(909nm)=5.02×10−20cm2, and σemi(1080nm)=7.03×10−20cm2. Continuous-wave laser action at 1080nm in LaAlO3:Nd3+ was obtained.