Blue Upconverted Emission Research Articles

Optimization of blue upconverted light emission based on fluoroindate glass matrix and subsequent chitosan functionalization.

Lanthanide-activated upconversion (UC) materials are fascinating for the new generation of biomedicine, because its unique ability to transform near-infrared light into visible light. Based on it, a set of fluoroindate glass matrices co-doped with Yb3+ and Tm3+ were prepared using the melting quenching technique. Then, the sample with the highest blue upconverted emission was milled and functionalized with chitosan (CS). The blue UC emission spectra of the glass increase with increasing Yb3+ concentration up to 1.8 mol%, then decreased. This could be attributed to the mechanism involved in the UC process, as confirmed by power dependence assessment. Also, according with the decay times the energy transfer efficacy of the samples is ∼50%. The milling of the glass resulted in particles of 44.8 ± 7.7 nm, which were successfully functionalized with CS. The CS-coated particles showed good cell viability, indicating that they could potentially be used in some biomedical applications.

Multifunctional broadband visible-light absorbing selenophene modified bodipy photosensitizers

Large π-conjugated organic systems with effective photosensitization are highly desirable for many photochemical applications. Herein, a series of π-conjugated selenophene-substituted boron dipyrromethene (known as bodipy) dyes (MB-Se, 2B–Se, MB-Se-2Br) were prepared by appending selenophene electron-donor to the core of bodipy acceptors via alkynyl bridge and their excited state properties were investigated. Optical spectroscopy revealed that although these three selenophene-substituted bodipy dyes have nearly identical molecular profiles, their photophysical properties and excited state dynamics are drastically different. Higher triplet quantum efficiency (ΦΔ = 82%) was observed for MB-Se, derivative in which α,β-positions of bodipy decorated with methyl substituents, compared to another dye 2B–Se, which showed inefficient triplet population (ΦΔ = 25%). Employing steady-state absorption and emission spectroscopies, we demonstrated that the designed selenophene-substituted bodipy dyes has excellent J-aggregation capabilities. Notably, the J-aggregates of selenophene-substituted bodipy dyes display NIR emission. The potential of devised selenophene-substituted bodipy dyes in triplet fusion upconversion was also demonstrated; a blue upconverted emission was realized upon irradiating the mixture of bodipy dyes and TIPS-AC acceptor with 589 nm CW-laser. The selenophene-substituted bodipy dyes were also confirmed to be a potent photodynamic therapeutic reagent; with an IC50 value of 0.76 μM, nearly 6 times lower than that of the iodide-appended bodipy photosensitizer (BDP-2I, 6.0 μM). This study hopes to provide valuable guidelines for the future development of multipurpose triplet photosensitizers.

Photo-physical studies of ultrasmall upconversion nanoparticles embedded organometallic complexes: Probing a dual mode optical sensor for hydrogen peroxide

Here, we report an upconversion nanoparticles (UCNPs) embedded organomettalic complex for detection of hydrogen peroxide (H2O2). The structural as well as the optical properties of the hybrid nanoparticles (HNPs) have been studies to confirm the interaction as well as energy transfer mechanism. The structural characterization confirm the weak interacting force between the UCNPs and the organic complex in HNPs. The optical studies reveal that, HNPs show characteristic optical behaviour of both the phases i.e. it gives an intense downconverted red emission under UV excitation, due to the presence of organic part (Eu3+ ion) as well as an efficient blue upconverted emission from inorganic part (Tm3+ ion) under NIR excitation. The energy transfer between the inorganic (Tm3+ ion) and the organic (Eu3+ ion) material has been observed, which confirms the effective attachment of both the phases in HNPs. The upconversion and downconversion emission properties, have been have successfully utilized for dual mode H2O2 detection.

Thermally Switchable Molecular Upconversion Emission

In this work a novel strategy is introduced to achieve thermally switchable emission from photon upconversion (UC) systems based on organic dyes. When these molecules were dissolved at low concentrations in phase-change media, a reversible, sharp, and nearly complete interconversion from blue upconverted emission to red luminescence was observed around the solid-to-liquid transition of the system. This result was rationalized in terms of dye aggregation, which selectively occurs in the solid state and dramatically enhances the inter-chromophoric energy transfer processes leading to UC. Notably, this behavior is extendable to different media and dyes, which allows an easy tuning of the switching temperature and emission colors. In addition, with proper selection of the phase-change medium, our strategy permits facile preparation of solid molecular materials showing photon UC at room temperature and even at sub-micromolar dye concentrations.

Synthesis of Yb<sup>3+</sup>/Tm<sup>3+</sup>Co-Doped MF<sub>2</sub> (M=Ca,Sr,Ba) Nanocrystals with Blue Up-Converted Fluorescence

A series of MF2:Yb3+/Tm3+(M=Ca, Sr, Ba) upconverted nanocrystals were synthesized by hydrothermal method. Polyvinylpyrrolidone(PVP) is an surfactant which can render the nanocrystals dispersible in water and ethanol. Upconverted emission was also detected in the red and NIR regions of the spectrum and assigned to the 1G4-3F4 (centered at 650 nm) and 3H4 -3H6 (centered at 800 nm) transitions, respectively. In addition, MF2:Yb3+/Tm3+ NCs show bright blue upconverted emission under the 980 nm excitation. As-synthesized MF2:Yb3+/Tm3+ luminescent NCs might find some potential applications in areas of photoluminescence and displays

Nd 3+ sensitized blue upconversion luminescence in Nd 3+/Pr 3+ co-doped Ge–Ga–S–CsBr chalcohalide glasses

The effect of CsBr/Ga ratio on the blue upconverted emission from Nd 3+/Pr 3+ in Ge–Ga–S–CsBr chalcohalide glasses was investigated. When CsBr/Ga was smaller than unity, the energy transfer from Nd 3+ to Pr 3+ ions was dominant and blue emission centered at ∼ 495 nm (Pr 3+: 3P 0 → 3H 4) was observed. On the contrary, the intensity of the upconversion luminescence from Nd 3+ increased at the expense of the blue emission when CsBr/Ga ratio exceeded unity. The possible relationship between the composition-dependent blue emission and the local environment of rare earth ions was discussed.

Investigation of Radiative and Nonradiative Relaxation by Two-Photon Resonant Excitation in Tm3+ Doped LaF3 Particles

Nano-scaled and micro-scaled Tm(3+)-doped LaF3 were prepared by a hydrothermal technique. Two-photon resonant excitation from the ground state 3H6 to the excited state 1D2 was fulfilled by two pulsed dye lasers tuned at 656 nm and 643 nm, respectively, which were resonant with the ground state absorption of 3H6 --> 3F2 and the excited state absorption of 3H4 --> 1D2. The time evolution of the corresponding state was investigated with blue upconverted emission by tuning the delay of two excitation lights. The results showed that the nonradiative relaxation of the 3F2 state was mainly affected by the confinement effect, while the radiative relaxation of 3H4 state was significantly influenced by the Tm3+ concentration.

Energy-transfer upconversion of rare earth ions in ionic crystals: Case of Tm 3+/Ho 3+-codoped LiYF 4 crystals

Up-conversion spectra of Tm 3+ and Ho 3+ ions in LiYF 4 crystals have been investigated at various temperatures between 10 and 320 K. The photoluminescence is investigated under excitation with Xe-lamp and laser diode. In addition to blue up-converted emission of Tm 3+ and Ho 3+ and green up-converted Ho 3+ emission, anti-Stokes emission bands are observed at 687 and 703 nm under excitation in the 3H 4 state of Tm 3+ with 785 nm laser diode. These bands are observed above 200 K, and their intensities increase exponentially with increasing temperature. They are attributed to endothermic Tm 3+ emission due to the transition to the 3H 6 ground state from the upper 3F 3 state, which is thermally populated from the 3H 4 state. Discussion is given on the optical process of green up-converted Ho 3+ emission, which is generated by the 785 nm laser diode excitation.

Infrared-to-visible conversion of radiation in YVO 4 crystals doped with Yb 3+ and Tm 3+ ions

Up-conversion processes in Yb 3+ and Tm 3+ doped YVO 4 crystals have been investigated upon continuous wave and short pulse excitation around 975 nm. The energy transfer efficiency from Yb 3+ to Tm 3+ has been experimentally assessed, using results of pulsed laser excitation. Infrared emission originating in the 3H 4 level and a considerably weaker blue emission originating in the 1G 4 level of Tm 3+ has been observed. The ratio of the IR to blue up-converted emission intensities is about 25:1 at room temperature. The dependence of the intensity of both emissions on the excitation power implies a two-step excitation mechanism of the 3H 4 emission and a three-step excitation one of the 1G 4 emission. Temperature dependencies of IR and blue up-converted emission have been discussed based on optical absorption and emission spectra and lifetimes recorded at several temperatures between 4.2 and 300 K. Up-converted blue emission in YVO 4:Yb+Tm is qualitatively similar to that observed in other matrices containing ytterbium and thulium but high intensity of up-converted IR emission associated with the 3H 4– 3H 6 transition of Tm 3+ may offer a laser potential.

Infrared-to-visible conversion of radiation in YVO4 crystals doped with Yb3+ and Tm3+ ions

Up-conversion processes in Yb 3+ and Tm 3+ doped YVO 4 crystals have been investigated upon continuous wave and short pulse excitation around 975 nm. The energy transfer efficiency from Yb 3+ to Tm 3+ has been experimentally assessed, using results of pulsed laser excitation. Infrared emission originating in the 3 H 4 level and a considerably weaker blue emission originating in the 1 G 4 level of Tm 3+ has been observed. The ratio of the IR to blue up-converted emission intensities is about 25:1 at room temperature. The dependence of the intensity of both emissions on the excitation power implies a two-step excitation mechanism of the 3 H 4 emission and a three-step excitation one of the 1 G 4 emission. Temperature dependencies of IR and blue up-converted emission have been discussed based on optical absorption and emission spectra and lifetimes recorded at several temperatures between 4.2 and 300 K. Up-converted blue emission in YVO 4 :Yb+Tm is qualitatively similar to that observed in other matrices containing ytterbium and thulium but high intensity of up-converted IR emission associated with the 3 H 4 – 3 H 6 transition of Tm 3+ may offer a laser potential.

Blue up-conversion luminescence and energy transfer process in Nd3+-Yb3+-Tm3+ co-doped ZrF4-based glasses

Up-conversion luminescence properties and energy transfer processes in Nd3+, Yb3+, and Tm3+ co-doped ZrF4-based fluoride glasses have been studied under 800 nm light excitation. Blue up-converted emission around 478 nm which can be assigned to the Tm3+: 1G4→3H6 transition, was strongly observed. Up-conversion luminescence intensity exhibited an YbF3-concentration dependence. Among Nd3+, Yb3+, and Tm3+, both Nd3+ and Tm3+ have ground state absorption bands due to the (2H9/2, F5/24) ←I9/24 and F43←3H6 transitions, respectively, which can be directly pumped by 800 nm light. However, no emissions were observed in Tm3+ singly doped and Tm3+-Yb3+ doubly doped glasses under 800 nm excitation. Therefore, a possible up-conversion mechanism may be proposed as follows: Energy transfer firstly occurs from Nd3+ to Yb3+ when Nd3+ is excited by 800 nm light, then the energy is transferred from Yb3+ to Tm3+ which is on the excited state and, finally, blue up-conversion emission of Tm3+ is observed through the Tm3+: 1G4→3H6 transition. It was also demonstrated that the energy on the Tm3+: 1G4 level was back-transferred to Nd3+ in the Nd3+ high-concentration region, quenching the up-conversion luminescence.

Highly efficient blue up-conversion of Tm 3+ in Nd 3+–Yb 3+–Tm 3+ co-doped ZrF 4-based fluoride glass

Up-conversion luminescence and energy-transfer processes in Nd 3+, Yb 3+ and Tm 3+ co-doped ZrF 4-based fluoride glasses have been studied under 800 nm light excitation. Blue up-converted emission around 478 nm which can be assigned to the Tm 3+: 1 G 4→ 3 H 6 transition, was strongly observed. Up-conversion luminescence intensity exhibited an YbF 3-concentration dependence. Among the Nd 3+, Yb 3+ and Tm 3+, Nd 3+ and Tm 3+ have ground state absorption bands due to the ( 2 H 9/2, 4 F 5/2)← 4 I 9/2 and 3 F 4← 3 H 6 transitions, respectively, which can be directly pumped by 800 nm radiation. However, no emissions were observed in Tm 3+ singly-doped and Tm 3+–Yb 3+ doubly-doped glasses under 800 nm excitation. Therefore, a possible up-conversion mechanism may be proposed as follows: energy-transfer firstly occurs from Nd 3+ to Yb 3+ when Nd 3+ is excited by 800 nm light, then the energy is transferred from Yb 3+ to Tm 3+ which is in the excited state and, finally, blue up-conversion emission of Tm 3+ is observed through the Tm 3+: 1 G 4→ 3 H 6 transition.