Near-infrared Upconversion Photoluminescence Research Articles

Structural, optical and temperature-sensing properties of LaOF:Yb3+, Tm3+ nanophosphor prepared by microwave-assisted hydrothermal synthesis

Luminescence thermometry forms a unique tool for remote temperature sensing by exploiting the variations in the luminescence properties of the probe. Thermometry based on the fluorescence intensity ratios (FIR) is a widely practiced approach due to them being a self-referenced measure. The quest for efficient temperature probes for thermometry led to the discovery of LaOF:Yb3+,Tm3+ upconversion nanoparticles, which were synthesized using a microwave-assisted hydrothermal synthesis method. Blue and near-infrared upconversion photoluminescence (UCPL) emission was observed under 980 nm laser excitation. The temperature-dependent UCPL was studied for their temperature sensing application. FIR of thermally coupled and non-coupled emission bands were calculated in the temperature range of 303 to 473 K. The thermometric characteristics such as absolute sensitivity, relative sensitivity and temperature uncertainty were also determined. The thermal stability of the UCNPs was established under continuous laser exposure operating at maximum power (2500mW). The reproducibility of the UCNPs was also determined by temperature cycling the UCNPs.

Yb3+, Er3+ and Tm3+ doped α-Sialon as upconversion phosphor

α-Sialon ceramics are mostly known for high-temperature and high-endurance applications due to their ability to withstand high structural load and their excellent chemical and thermal stability. Here we demonstrate functional α-Sialon ceramics with photon upconversion properties. Intense visible and near-infrared upconversion photoluminescence is observed in Yb3+, Er3+, and Tm3+ doped α-Sialon ceramics prepared by hot press sintering. Clear evidence of α-Sialon formation with the incorporation of Yb3+, Er3+ and Tm3+ ions in the lattice has been established. Emission bands at 498 nm, 551 nm, 662 nm and 802 nm are observed as a result of the two-photon absorption process. The decay behavior of the emission bands suggests the existence of efficient energy transfer from Yb3+ to Er3+ and Tm3+ ions. The possibility of temperature sensing properties has been investigated via high-power laser excitation. These findings could possibly extend the usefulness of Yb3+, Er3+ and Tm3+ doped α-Sialon as an upconversion phosphor material.

Efficient near-infrared up-conversion photoluminescence in carbon nanotubes.

Photoluminescence phenomena normally obey Stokes' law of luminescence according to which the emitted photon energy is typically lower than its excitation counterparts. Here we show that carbon nanotubes break this rule under one-photon excitation conditions. We found that the carbon nanotubes exhibit efficient near-infrared photoluminescence upon photoexcitation even at an energy lying >100–200 meV below that of the emission at room temperature. This apparently anomalous phenomenon is attributed to efficient one-phonon-assisted up-conversion processes resulting from unique excited-state dynamics emerging in an individual carbon nanotube with accidentally or intentionally embedded localized states. These findings may open new doors for energy harvesting, optoelectronics and deep-tissue photoluminescence imaging in the near-infrared optical range.

Visible and near-infrared upconversion photoluminescence in lanthanide-doped KLu3F10 nanoparticles

Upconversion (UC) photoluminescent nanocrystals of Ln3+-doped KLu3F10 have been synthesized via a facile and environmentally-friendly hydrothermal route.

Blue and near-infrared up-conversion photoluminescence and dielectric relaxation of Tm3+/Yb3+ co-doped (Bi, Y)2Ti2O7 pyrochlore thin films

The blue emission and near-infrared (NIR) up-conversion photoluminescence and dielectric relaxation of Tm3+/Yb3+ co-doped (Bi, Y)2Ti2O7 pyrochlore thin films prepared by a chemical solution deposition method have been investigated. The pyrochlore phase has been maintained for all compositions. Intense blue and NIR emission can be detected on the thin films on fused silica substrates excited by a 980nm diode laser. Three UC emission bands centered at 480nm, 665nm, and 800nm in the spectra can be assigned to 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions of Tm3+ ions, respectively. The dependence of UC emission intensity on pumping power indicates that the blue emission of the thin films follows a three-photon process while the NIR emission is a two-photon process. The thin films also exhibit a relatively high dielectric constant and a low loss as well as good bias voltage stability. Temperature and frequency dependent dielectric relaxation has been investigated. This study suggests that Tm3+/Yb3+ co-doped (Bi, Y)2Ti2O7 thin films can be applied to new multifunctional photoluminescence dielectric thin-film devices.

Upconversion Emission Properties of Erbium- and Ytterbium-Doped Potassium Lithium Tantalate Niobate Ceramics

We investigate the luminescence properties of erbium-doped and erbium-ytterbium-codoped potassium lithium tantalate niobate ceramics prepared by the solid phase syntheses method. The crystalline structure and surface morphology of these ceramics are tested by x-ray diffraction and scanning electron microscopy. The green, red, and near-infrared upconversion photoluminescence properties are analyzed by the steady-state spectra under 975 nm and 800 nm excitations. These ceramics are well sintered and tetragonal tungsten type crystalline structure with the 4mm point group and the P4bm space group. The Er3+ upconversion emission integrated intensities increase with the increase in Er3+ ion concentration, while the green emission decreases with the increase in Yb3+ ion concentration under the 800 nm excitation. An effective energy back transfer process from the Er3+ 4S3/2 state to Yb3+ ground state plays an important role in enhancing the red emission and weakening the green emission.

Intense visible and near-infrared upconversion photoluminescence in colloidal LiYF₄:Er³+ nanocrystals under excitation at 1490 nm.

We report intense upconversion photoluminescence (PL) in colloidal LiYF(4):Er(3+) nanocrystals under excitation with telecom-wavelength at 1490 nm. The intensities of two- and three-photon anti-Stokes upconversion PL bands are higher than or comparable to that of the Stokes emission under excitation with low power density in the range 5-120 W/cm(2). The quantum yield of the upconversion PL was measured to be as high as ∼1.2 ± 0.1%, which is almost 4 times higher than the highest upconversion PL quantum yield reported to date for lanthanide-doped nanocrystals in 100 nm sized hexagonal NaYF(4):Yb(3+)20%, Er(3+)2% using excitation at ∼980 nm. A power dependence study revealed that the intensities of all PL bands have linear dependence on the excitation power density, which was explained by saturation effects in the intermediate energy states.

Monodisperse NaYbF4 : Tm3+/NaGdF4 core/shell nanocrystals with near-infrared to near-infrared upconversion photoluminescence and magnetic resonance properties

We report core/shell NaYbF(4):Tm(3+)/NaGdF(4) nanocrystals to be used as probes for bimodal near infrared to near infrared (NIR-to-NIR) upconversion photoluminescence (UCPL) and magnetic resonance (MR) imaging. The NaYbF(4):Tm(3+) nanocrystals were previously reported to produce the intense NIR-to-NIR UCPL peaked at ∼800 nm under excitation at ∼975 nm. We have found that the growth of a NaGdF(4) shell on surface of the NaYbF(4):Tm(3+) nanocrystals results in the increase in the intensity of UCPL of Tm(3+) ions by about 3 times. Unlike biexponential PL decay of NaYbF(4):Tm(3+) nanocrystals, the PL decay of NaYbF(4):Tm(3+)/NaGdF(4) core/shell nanocrystals is single exponential and of longer lifetime due to the suppression of surface quenching effects for Tm(3+) PL. The growth of a NaGdF(4) shell on surface of the NaYbF(4):Tm(3+) nanocrystals also provides high MR relaxivity from paramagnetic Gd(3+) ions contained in the shell. The T1-weighted MR signal of the (NaYbF(4):2% Tm(3+))/NaGdF(4) nanoparticles was measured to be about 2.6 mM(-1)s(-1). Due to the combined presence of efficient optical and MR imaging capabilities, nanoprobes based on NaYbF(4):Tm(3+)/NaGdF(4) fluoride nanophosphors can be considered as a promising platform for simultaneous bimodal PL and MR bioimaging.