ABSTRACT
This work demonstrates the temperature (18-312â K) impact on Tm3+ up-conversion luminescence in core-shell structured NaYF4:Tm3+, Yb3+ nanoparticles excited at 976â nm. As the temperature decreases from room temperature to 18â K, Tm3+ up-conversion luminescence bands intensities greatly increase, an average of 60-fold, emitting intense blue and ultraviolet radiation. Tm3+ up-conversion luminescence spectra measurements at different temperatures reveal that three thermal quenching mechanisms are responsible for observed variations in Tm3+ up-conversion luminescence spectra. These three quenching mechanisms are related to the excitation radiation absorption, Stark sublevel population, and energy transfer from Yb3+ to Tm3+.
ABSTRACT
We demonstrate the generation of high-order harmonics of laser pulses in palladium and cadmium plasmas. We adjusted the wavelength of driving pulses to investigate the resonance enhancement in different ranges of extreme ultraviolet region. The summation of incommensurate waves during the two-color pump of Pd and Cd plasmas allowed the generation of a broader range of harmonics. The theoretical aspects of the two-color pump of the laser-induced plasma are discussed.
ABSTRACT
This publication offers an economically promising method of persistent luminescent silicate glass synthesis that does not involve high temperatures or ready-made (separately synthesized) PeL particles. In this study, we demonstrate the formation of SrAl2O4 doped with Eu, Dy, and B in a SiO2 glass structure using the one-pot low-temperature sol-gel synthesis method. By varying the synthesis conditions, we can use water-soluble precursors (e.g., nitrates) and a dilute aqueous solution of rare-earth (RE) nitrates as starting materials for SrAl2O4 synthesis, which can be formed during the sol-gel process at relatively low sintering temperatures (600 °C). As a result, translucent, persistently luminescent glass is obtained. The glass shows the typical Eu2+ luminescence and the characteristic afterglow. The afterglow duration is about 20 s. It is concluded that the slow drying procedure (2 weeks) is optimal for these samples to sufficiently get rid of the excess water (mainlyOH groups) and solvent molecules that can influence the strontium aluminate luminescence properties and have a pernicious effect on the afterglow. It can also be concluded that boron is playing a crucial role in the formation of trapping centers needed for PeL processes in the PeL silicate glass.
ABSTRACT
The authors report the third-harmonic generation, nonlinear refraction, and nonlinear absorption in HgS quantum dot (QD) suspensions and films using the nanosecond and femtosecond pulses. High conversion efficiency (7 × 10-4) towards the third harmonic (TH) of the 900-1700 nm, 150 fs laser in the thin (70 nm) films containing HgS QDs deposited on the glass substrates is obtained. The authors analyze spectral dependencies of the TH, nonlinear refractive indices, and nonlinear absorption coefficients of QDs in the 500-1700 nm range and discuss the relation between the TH process and the low-order nonlinear optical properties of these quantum dots.
ABSTRACT
We characterize the nonlinear optical properties of synthesized Bi2Te3 nanoparticle-contained thin films using the tunable femtosecond laser in the spectral range of 400-1000â nm. These nanoparticles possess a strong saturable absorption and positive nonlinear refraction (-6.8×10-5 cm W-1 in the case of 500â nm, 150 fs probe pulses, and 3×10-10 cm2 W-1 in the case of 400â nm, 150 fs probe pulses, respectively). The spectral, intensity, and temporal variation of saturable absorption and nonlinear refraction of the thin films containing exfoliated Bi2Te3 nanoparticles are discussed.
ABSTRACT
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.
Subject(s)
Luminescence , TemperatureABSTRACT
We report measurements of the saturated intensities, saturable absorption, and nonlinear refraction in 70-nm thick films containing 4 nm HgTe quantum dots. We demonstrate strong nonlinear refraction and saturable absorption in the thin films using tunable picosecond and femtosecond pulses. Studies were carried out using tunable laser pulses in the range of 400-1100 nm. A significant variation of the nonlinear refraction along this spectral range was demonstrated. The maximal values of the nonlinear absorption coefficients and nonlinear refractive indices determined within the studied wavelength range were -2.4 × 10-5 cm2 W-1 (in the case of 28 ps, 700 nm probe pulses) and -3 × 10-9 cm2 W-1 (in the case of 28 ps, 400 nm probe pulses), respectively. Our studies show that HgTe quantum dots can be used in different fields e.g., as efficient emitters of high-order harmonics of ultrashort laser pulses or as laser mode-lockers.
