Investigation of upconversion phenomenon in Y1-xLn3+x(BTC)(DMF)2(H2O) and Y0.8-xYb0.2Ln3+x(BTC)(DMF)2(H2O) metal organic frameworks

In this study, Y1-xLn3+x(BTC)(DMF)2(H2O) and Y0.8-xYb0.2Ln3+x(BTC)(DMF)2(H2O) metal organic frameworks (MOFs), which structure included lanthanide ions, Ln3+ (Er3+, Ho3+, Tm3+, Yb3+, Nd3+), suitable for monitoring the upconversion phenomenon, have been synthesised. For this purpose the precursor of the organic moiety, benzene-1,3,5-tricarboxylic acid (BTC), as one of the simplest and very frequently cited carboxylic acid analogues in MOF syntheses, has been selected. By characterising upconversion properties of new MOFs it was determined that only Er3+ can be used as an activator for one centre luminescence upconversion by a ground state absorption/ excited-state absorption (GSA/ESA) mechanism, while with Yb3+, Ho3+, Tm3+ and Nd3+ ions the upconversion was not observed. It was also established that BTC cannot initiate triplet–triplet annihilation upconversion (TTA-UC) as this mechanism sensitizer. Yb3+–Er3+ and Yb3+–Ho3+ ion pairs as a sensitizeractivator were suitable for two-centre luminescence upconversion by a GSA/ excited-state upconversion (GSA/ESU) mechanism. A pair of Yb3+–Tm3+, contrary as shown in the literature review, does not exhibit upconversion properties in the synthesised MOFs.

Extraction of temperature-dependent exciton-polariton damping in InP bulk crystal

The temperature dependence of exciton-polariton damping in InP bulk crystal was extracted by the method of integrated absorption. The extraction procedure excluding the contribution of inhomogeneous broadening into the exciton ground state absorption linewidth is graphically illustrated. The extracted temperature-dependent damping is analyzed regarding the primary dissipative mechanism in order to determine the material parameters of exciton-polariton scattering by acoustic and optical phonons.

Sub–single-exciton lasing using charged quantum dots coupled to a distributed feedback cavity

Colloidal semiconductor quantum dots (QDs) are attractive materials for realizing highly flexible, solution-processable optical gain media, but they are difficult to use in lasing because of complications associated with extremely short optical-gain lifetimes limited by nonradiative Auger recombination. By combining compositional grading of the QD’s interior for hindering Auger decay with postsynthetic charging for suppressing parasitic ground-state absorption, we can reduce the lasing threshold to values below the single-exciton-per-dot limit. As a favorable departure from traditional multi-exciton–based lasing schemes, our approach should facilitate the development of solution-processable lasing devices and thereby help to extend the reach of lasing technologies into areas not accessible with traditional, epitaxially grown semiconductor materials.

Increasing the triplet lifetime and extending the ground-state absorption of biscyclometalated Ir(iii) complexes for reverse saturable absorption and photodynamic therapy applications

Tuning the photophysics of cationic Ir(iii) complexes via π-expansive ligands dramatically impacts their applications as broadband reverse saturable absorbers and in photodynamic therapy and theranostics.

Investigations of Non-Linear Absorption of Q-Switching Saturable Absorbers and Determination of their Main Parameters

Investigations of non-linear absorption of q-switching absorbers were carried out. Three types of saturable absorbers were examined (Cr4+:YAG at the wavelength of 1064 nm, V3+:YAG and Co2+:YAG at the wavelength of 1332 nm) and their principal parameters were estimated. To appropriately determine these parameters 48 samples of Cr4+:YAG, 42 samples of V3+:YAG and 26 samples of Co2+:YAG were investigated making the results more reliable. Three different models of analysis of saturation effect were described and the best one chosen. Using the best model for the analysis the main parameters of the saturable absorbers were determined. On the basis of so many samples the standard deviation of the ground state absorption cross section, the excited state absorption cross section and the unsaturable losses were calculated showing how the value of these parameters may differ even for the same type of crystal.

Study of UV fluorescences induced from 4f3 T 4f25d multistep absorptions of Nd3+ions in YLiF4 and LuLiF4 crystals

Nd3+ ultraviolet (UV) fl uorescence induced by multiphotonic laser excitations was studied in doped Nd:YLiF4 (YLF) and Nd:LuLiF4 (LLF) crystals by using the time resolved spectroscopy technique. The UV luminescences are due to transitions between the 4f25d and the 4f3 electronic confi gurations of Nd3+ ions. The 4f25d confi guration can be reached by direct pumping or by multiphotonic excitation, both processes give rise to the UV band emission with structure due to the strong phonon coupling expected for 5d orbital involvement in the transition. The multiphotonic excitation process is due to three photons (532 nanometers [nm]) sequential absorptions by metastable levels of the 4f3 confi guration split by crystalline local fi eld. The sequential excitation of Nd by the laser excitation is attributed to the 4I9/2 + 532 nm T 4G7/2 ground state absorption followed by the 4G7/2 + 532 nm T 2F5/2 and 2F5/2 + 532 nm T 4f25d excited state absorptions. The UV emissions due to 4f25d confi guration are parity allowed, having lifetime of 35 nanoseconds (ns) in contrast to UV emissions from 4f3 confi guration which are induced by two absorption steps and are parity forbidden showing longer lifetime of 8 microseconds (ms) and narrow lines. The polarization effects of the UV emissions were studied and their behaviors are dependent on the excited state confi guration involving or not involving the 5d orbital. The allowed UV emission positions were affected by the host variation more than the ones originated from the 4f3 confi guration as expected. The electronic energy of the 4f25d confi guration shifts to lower energy for increasing the crystal fi eld.