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Advanced instrumentation and modern analysis tools such as transmission electron microscopy (TEM) have led to phenomenal progress in understanding crystallization, in particular from solution, which is a prerequisite for the design-based preparation of a target crystal. Nevertheless, little has been understood about the crystallization pathway under high-temperature annealing (HTA) conditions. Metal oxide crystals are prominent materials that are usually obtained via HTA. Despite the widespread application of hydro-/solvothermal methods on the laboratory scale, HTA is the preferred method in many industries for the mass production of metal oxide crystals. However, poor control over the morphology and grain sizes of these crystals under extreme HTA conditions limits their applications. Here, applying ex-situ TEM, the transformation of a single amorphous spherical submicrometer precursor particle of SrAl

Development of red-emitting phosphors have gained enormous interest in recent year, due to their great potential for biological applications as well as display panels and solid-state lighting. Here, we present luminescence spectroscopy of deep-red-emitting CaAl12O19 (CA6) and SrAl12O19 (SA6) nanocrystals doped with Eu3+. CA6:Eu3+ and SA6:Eu3+ hexagonal nanoparticles (NPs) were prepared via a solvothermal reaction followed by a post-annealing process at 1150 °C. The luminescence spectra were obtained both at 298 and 5 K. Unaccustomed for Eu3+, the strongest emission was observed to originate from the 5D0→7F4 transition. Furthermore, emissions from the higher excited states (5D1-3) of the f-configuration of Eu3+ were also observed in these NP hosts at room temperature. In addition to the bands assigned to Eu3+ on the high symmetry D3h site, additional bands assigned to lower symmetry charge compensated sites have been identified. Crystal field (CF) parameters were obtained for the Eu3+ ion in SA6 compound, and the energy levels were estimated theoretically, which agreed well with the experimental values.

Rare-earth-doped strontium aluminates find many applications. One particular property is persistent phosphorescence. SrAl2O4:Eu2 +, Dy3 + and Sr4Al14O25: Eu2 +, Dy3 + are as of today among the best non-radioactive persistent phosphors with afterglow durations exceeding 10 h. In this chapter, we first present the phase diagram and crystal structures of strontium aluminates, before addressing the doping with rare earth ions in these hosts. After presenting the spectroscopy of Eu2 + in strontium aluminates, we summarize experimental results concerning defects and co-doping in relation to the persistent emission. Finally, we discuss the current understanding of processes underlying persistent luminescence in these inorganic phosphors.

We have measured room temperature and low temperature luminescence spectra of Eu3+ in SrAl2O4:Eu3+/2+. The powder samples were synthesized in reducing atmosphere above 1200 °C, cooled down to room temperature in the same atmosphere, and heated again to 750 °C in air. The analysis of the emission spectra of Eu3+ showed the presence of multiple sites for this ion, revealing that many different charge compensating defects are located in close vicinity to the europium ions. These defects can be positioned in each of the two void sites identified in the crystal structure of SrAl2O4. Lifetime measurements reveal the presence of very short-lived excited Eu3+ species with lifetimes around 0.7 μs, in addition to species with lifetimes around 1.6 ms. These very short lifetimes are postulated to be related to intervalence charge transfer with few remaining divalent Eu2+ ions which had not been oxidized by the thermal treatment in air. This type of intervalence charge transfer between divalent to the trivalent rare earth ion could be crucially associated to processes involved in the afterglow of the persistent phosphor SrAl2O4:Eu2+,Dy3+.

Through functionalizing of isonicotinic acid hydrazide (INAH) on to fumed silica nanoparticles, a novel fluorescent nanomaterial (fumed-Si–INAH) was synthesized and characterized using various techniques including FT-IR, SEM, and TGA. Next, interaction of the new nanofluorophore material with metal cations was studied spectrofluorimetrically. The fluorescence evaluation of fumed-Si–INAH towards a wide range of cations including Pb2+, Cd2+, Zn2+, Cu2+, Fe2+, Ca2+, Ni2+, Mn2+, Mg2+, Co2+, Na+, Hg2+, Cr3+, and K+ revealed that fumed-Si–INAH was a highly selective optical sensor for Hg2+ and Cr3+ ions in a wide range of pH in water. Thus, it was applied as a fluorescent bulk sensor for Hg2+ and Cr3+ ions. The detection limits were obtained to be 3.5 × 10−5 and 4.2 × 10−5 M for Hg2+ and Cr3+, respectively.

1,2-Bis(2-hydroxymethylphenoxy)ethane was synthesized and characterized by FT-IR and 1 H NMR spectroscopy, and single crystal X-ray diffraction method. The sensing ability of the sensor was studied in the presence of different cations and anions. Following the excitation wavelengths at 275 nm in EtOH/H 2 O (1:9, v/v) and 310 nm in MeCN/H 2 O (1:9, v/v), two distinct emissions at 305 and 356 nm were obtained, respectively. Fe 3+ and CN − ions were successfully detected in EtOH/H 2 O and MeCN/H 2 O mixtures, respectively. While the fluorescence intensity of the sensor quenched considerably in the presence of Fe 3+ cation at 305 nm, it enhanced in the presence of CN − anion at 356 nm. Selectivity of the sensor toward these ions was verified in the presence of a variety of common interfering ions. The detection limits of Fe 3+ and CN − were calculated as 5.4 × 10 −9 mol L −1 and 1.9 × 10 −8 mol L −1 , respectively which shows the high sensitivity of the sensor toward the target ions. Finally, the interaction of the sensor and CN − anion was determined by computational studies.

The dysprosium and boron effect on the emission properties of europium-doped SrAl2O4 samples has recently attracted considerable attention due to their high brightness and long afterglow. Here, the influence of both cations, Dy3+ and B3+, on the spectroscopic properties of the europium free samples SrAl2O4:Dy3+ and SrAl2O4:Dy3+, B3+ has been investigated in order to get more insights concerning the mechanism by which they enhance the afterglow. Unique features have been observed in their excitation and emission spectra that show on one hand the lattice defects induced by the replacement of Sr2+ by Dy3+ and proves the existence of different crystallography sites for the Dy3+ ions and on the other hand, the local distortion of the energy levels of Dy3+ ions in the presence of B3+.

The extraordinary long phosphorescence of SrAl2O4:Eu2+:Dy3+ has been widely studied in powder samples because of its broad range of applications in this form and despite the fact that the bulk material shows higher intensity emission and longer afterglow. However, the investigation of SrAl2O4:Eu2+:Dy3+ crystals that, unlike the powder, do not contain surface defects, would allow a better insight into the mechanism that governs the long-lasting phosphorescence of this co-doped material. Thus, a SrAl2O4:Eu2+:Dy3+ single crystal was studied in detail by absorption spectroscopy and photoluminescence, including a novel estimation of its extinction coefficient. In addition, thermoluminescence measurements and wavelength-dependent quantum efficiency measurements have been performed to improve the understanding of the role of both europium and dysprosium ions in the corresponding persistent phosphorescence mechanism.

A simple but versatile nanoporous silica-based optical sensor was synthesized and characterized using different techniques such as XRD, BET, TGA, and FT-IR. The sensing ability of the sensor was examined upon addition of a wide variety of cations and anions in water both visually and by fluorescent spectroscopy. The color of the water suspension of the sensor changed from beige to brown in the presence of the Fe3+ ion and its fluorescence intensity enhanced upon addition of Al3+ and CN− following excitation at λ = 390 nm. The rest of the tested ions neither induce remarkable changes in the optical properties of the sensor nor interfere in the detection of the target ions indicating the selectivity of the sensor toward the detected ions. Linear changes of the optical properties of the sensor as a function of the concentrations of the target ions was proved. The detection limits for all three ions were also calculated. Finally, investigation of the logic behavior of the sensor revealed its capability of functioning as a XOR-type fluorescent sensor with Al3+ and CN− ions as inputs.

An organic–inorganic hybrid optical sensor (LQS) was prepared with post grafting of 8-hydroxy-5-quinoline sulfonic acid onto the surface of LUS-1. Its structure was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption, and thermogravimetry analysis (TGA). The fluorescence evaluation of LQS toward a wide range of cations including Na+, Mg2+, Al3+, K+, Ca2+, Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ revealed that LQS was a highly selective optical sensor for Fe3+ in a wide range of pH in pure water.

An iminocrown ether was synthesized and its fluorescence properties were studied in the presence of a variety of cations and anions in 99 % aqueous medium. The results revealed the interesting ability of the iminocrown ether in discriminately detection of Cr(III) and Cr(VI) ions in addition to detection of Hg(2+) ion. Among various environmentally relevant metal ions, Cr(3+) and Hg(2+) enhanced and quenched the fluorescence emission, respectively and among anions only dichromate ion, Cr(VI), quenched the emission while the rest of ions insignificantly influenced the fluorescence emission. Selectivity of the iminocrown ether was also investigated and proved in the presence of excess of common competing ions. Furthermore, the fluorescence intensity of the iminocrown ether was studied as a function of concentrations of the three ions by performing a titration experiment for each one of them. The detection limits of 5.36 × 10(-8), 2.06 × 10(-6), and 7.49 × 10(-8) mol L(-1) were also calculated for Hg(2+), Cr(3+), and Cr(VI), respectively.

A novel organic–inorganic silica-based fluorescent probe was designed, synthesized and characterized by different techniques such as XRD, BET, TGA, and FT-IR. The fluorescence properties of the probe were studied in the presence of a variety of metal-ions in water. The results revealed that various metal-ions negligibly vary the emission intensity of the probe except for Hg2+, which quenched the intensity dramatically. The selectivity of the probe toward Hg2+ ion was further investigated in the presence of common competing metal-ions and the results demonstrated the high selectivity of the probe toward Hg2+ ion. The fluorescence emission of the probe was also studied as a function of the concentration of Hg2+ ion. A nanomolar limit of detection was estimated for Hg2+, indicating a high sensitivity. Furthermore, the probe showed INHIBIT-type logic behavior with Hg2+ and H+ as inputs. Also, the optimum pH range was studied in addition to reversibility and real world applicability of the probe.