Up-Conversion Luminescence Processes in NaLaF4 Doped with Tm3+ and Yb3+ and Dependence on Tm3+ Concentration and Temperature

In this work, luminescence processes in polycrystalline NaLaF4:Tm3+ and NaLaF4:Tm3+,Yb3+ materials were studied. Luminescence spectra and decay kinetics measurements were performed for NaLaF4 doped with various Tm3+ concentrations (0.01, 0.1, 0.5, 1, and 2 mol%) under direct excitation to 3P0, 1D2, 1G4, and 3H4 states. It was found that some of the Tm3+ excited states are more affected by Tm3+ concentration than other states. Under infrared excitation of Yb3+, energy transfer to Tm3+ occurred and intensive ultraviolet and blue up-conversion luminescence was observed. Possible up-conversion mechanisms are discussed. Spectroscopic measurements show that long-duration excitation radiation reduces ultraviolet up-conversion luminescence intensity, and this intensity reduction is related to sample heating due to high excitation radiation density and a poor heat sink from samples. It was found that sample configuration for spectroscopic measurements is crucial to correctly describe measured up-conversion luminescence spectra.

Зависимость характеристик узких линий люминесценции в наноалмазах от параметров возбуждения и температуры

The influence of the excitation parameters and temperature on the spectral characteristics of narrow photoluminescence lines in nanodiamonds obtained by chemical vapor deposition is investigated. It is shown that the ratio of the line intensities in the spectrum depends on the wavelength and power of the excitation radiation. For some lines, with increasing power, a shift in the position of their maximum and broadening is also observed. After irradiation of nanodiamonds with a laser beam with a power density of ~1.2·105 W/cm2, the relative line intensities change. With increasing temperature in the range 79 - 300 K, temperature quenching of their intensity is observed.

Нелинейный магнитооптический резонанс в парах -=SUP=-87-=/SUP=-Rb: влияние паразитных магнитных полей и интенсивности возбуждающего излучения на основные характеристики эффекта в ячейках с антирелаксационным покрытием

The nonlinear Hanle effect is generally considered in the modern literature as a particular case of coherent population trapping (CPT) at degenerate Zeeman sublevels of the ground atomic state. The shape, amplitude, and sign of observed resonances and their dependence on the excitation parameters and observation geometry were investigated theoretically and experimentally in many studies because of the wide range of application of this effect. The sensitivity of Hanle resonances to the experimental conditions increases significantly in cells with antirelaxation coating, because the atomic ensemble retains its coherence after a large number of collisions with the cell walls. In this paper, the main attention is paid to the joint influence of the excitation radiation intensity and spurious magnetic fields on CPT resonances observed in fluorescence. The theoretical description is based on the numerical solution of an algebraic system of equations for density matrix $$\hat {\rho }$$ in the formalism of irreducible tensor operators. The parameters relating different polarization moments in each equation are visualized using the modified sparse matrix of the system. It is established by numerical simulation that the shape, width, amplitude, and sign of nonlinear magnetooptical resonances change nonmonotonically with a change in the parameters of the excitation radiation and atomic system. The presented theoretical results are in good agreement with the experimental data obtained under various conditions.

Фотолюминесценция ниобата лития, легированного медью

The photoluminescence (PL) of copper-doped lithium niobate single crystals is studied using different UV–Vis light-emitting diodes and a pulse-periodic laser with a wavelength of 266 nm as excitation radiation sources. With the resonance excitation from a 527-nm light-emitting diode, the intensity of PL increases sharply (by two orders of magnitude). When using a 467-nm light-emitting diode for excitation, the PL spectrum is characterized by the presence of multiphonon lines in the range of 520–620 nm.

Scattered and Fluorescent Photon Track Reconstruction in a Biological Tissue

Appropriate analysis of biological tissue deep regions is important for tumor targeting. This paper is concentrated on photons’ paths analysis in such biotissue as brain, because optical probing depth of fluorescent and excitation radiation differs. A method for photon track reconstruction was developed. Images were captured focusing on the transparent wall close and parallel to the source fibres, placed in brain tissue phantoms. The images were processed to reconstruct the photons most probable paths between two fibres. Results were compared with Monte Carlo simulations and diffusion approximation of the radiative transfer equation. It was shown that the excitation radiation optical probing depth is twice more than for the fluorescent photons. The way of fluorescent radiation spreading was discussed. Because of fluorescent and excitation radiation spreads in different ways, and the effective anisotropy factor,geff, was proposed for fluorescent radiation. For the brain tissue phantoms it were found to be0.62±0.05and0.66±0.05for the irradiation wavelengths 532 nm and 632.8 nm, respectively. These calculations give more accurate information about the tumor location in biotissue. Reconstruction of photon paths allows fluorescent and excitation probing depths determination. Thegeffcan be used as simplified parameter for calculations of fluorescence probing depth.