Halide perovskites, including CsPbX (X = Cl, Br, I), have gained much attention in the field of optoelectronics. However, the toxicity of Pb and the low photoluminescence quantum yield (PLQY) of these perovskites hamper their use. In this work, new halide materials that meet the requirements of: (i) nontoxicity, (ii) high PLQY, and (iii) ease of fabrication of thin films via the solution process are explored. In particular, copper(I) halide compounds with low-dimensional electronic structures are considered. Cs Cu I has a 0D photoactive site and exhibits blue emission (≈445 nm) with very high PLQYs of ≈90 and ≈60% for single crystals and thin films, respectively. The large exciton binding energy of ≈490 meV explains well the 0D electronic nature of Cs Cu I . Blue electroluminescence of Pb-free halides is demonstrated using solution-derived Cs Cu I thin films.

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Concentration changes of interstitial oxygen molecules (O2) in amorphous SiO2(a-SiO2) thermally annealed in oxygen atmosphere were examined by the O2 photoluminescence at 1272 nm excited with 765-nm light of titanium sapphire laser. This highly sensitive technique allows the time- and temperature-dependent concentration changes of interstitial O2 due to their incorporation from an oxygen atmosphere to be directly measured. The data provide the dissolution rate, the diffusion coefficient, and the solubility of interstitial O2 in a-SiO2 and are able to exclude interferences from other forms of mobile oxygen species in a-SiO2. These observations confirm that O2 molecules are incorporated into a-SiO2 without separating into monoatomic species, diffuse in a-SiO2 without extensive interaction with the a-SiO2 network, and play a primary role in the thermal oxidation of silicon.

The decay constants of the a1Δg(v=0)→X3Σg-(v=0) infrared photoluminescence (PL) of isotopically-labeled oxygen molecules 16O18O and 18O2 dissolved in the interstitial voids of a-SiO2 are ∼1.7 and ∼2.5 times larger than that of 16O2. This difference originates from the isotope shift in the energy of the nonradiative transitions from the a state to the vibronic levels of the X ground state. Calibration of the PL quantum yield using the measured decay constants is essential to measure the correct concentration of isotopically-labeled interstitial O2.

Bulk heterojunction (BHJ) based on a donor (D) polymer and an acceptor (A) fullerene derivative is a promising organic photovoltaic. Here, we investigated the femtosecond charge dynamics after acceptor excitation in poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b '] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediyl]] (PTB7)/[6,6]-phenyl C71-butyric acid methyl ester (PC70BM), which is a low-gap (Egap≈1.6 eV) organic photovoltaic. We observed fast conversion from the acceptor exciton (A*) to the donor polaron (D+) within τrise = 0.45 ps. The fast carrier formation is ascribed to the prompt charge transfer of an electron from the D highest occupied molecular orbital (HOMO) to the A HOMO.

Electronic phase diagram has been derived for the Prussian-Blue-type cyano-bridged transition-metal compound, Na 0.84−␦ Co͓Fe͑CN͒ 6 ͔ 0.71 · 3.8H 2 O ͑0.0Յ ␦ Յ 0.61͒, as a function of the hole concentration ␦ of the d-electron system. The mother compound ͑␦ =0͒ takes the Co 2+ ͑t 2g 5 e g 2 : S =3/ 2͒ and Fe 2+ ͑t 2g 6 : S =0͒ configuration and is paramagnetic down to zero temperature. At room temperature, the holes are selectively introduced on the Fe site. A slight hole doping ͑␦ = 0.13͒ causes the charge-transfer ͑CT͒ transition, that is, cooperative electron transfer from the Co 2+ site to the Fe 3+ site, with a decrease in temperature below T CT Ϸ 250 K. With a further increase in ␦, T CT slightly decreases from Ϸ230 K at ␦ = 0.24 to ϳ210 K at ␦ = 0.61. Accordingly, the nature of the transition changes from the second-order type to the first-order type. In all the concentration ranges, the high-temperature ͑HT͒ phase is metastable even at low temperature. In this metastable phase, the Fe 3+ ͑t 2g 5 : S =1/ 2͒ species mediate the ferromagnetic exchange coupling between the adjacent Co 2+ spins. The ferromagnetic transition appears at ␦ = 0.39, and the transition temperature T C increase from 7 K at ␦ = 0.39 to 13 K at ␦ = 0.61. Based on these experimental data, we will discuss the significant roles of the coupling between the charge, spin, and lattice degrees of freedom in the transition-metal cyanides.