Christian Pflitsch

Bio: Christian Pflitsch is an academic researcher from University of Duisburg-Essen. The author has contributed to research in topics: Metalorganic vapour phase epitaxy & Thin film. The author has an hindex of 11, co-authored 23 publications receiving 545 citations.

Light emitting diode excitation of Cr3+:Al2O3 as thermographic phosphor: experiments and measurement strategy

Abstract: Light emitting diode (LED) excitation of thermographic phosphors for temperature measurements was investigated in the present work. A near-UV and a green LED excited the phosphorescence of sol?gel deposited chromium-doped alumina (Cr3+:Al2O3, ruby) on silicon in different experiments. The influence of the pulse length on signal intensity was measured and is discussed theoretically. From this, measurement strategies are recommended in order to obtain high signal levels. The temperature-dependent phosphorescence between room temperature and 800 K is compared to previously obtained laser excited phosphorescence. The phosphorescence decay time of the ruby films is found to be slightly dependent on the excitation pulse duration but neither on the excitation wavelength nor on the oxygen partial pressure in the atmosphere. In many situations the less expensive LED excitation appears to be a good alternative to the laser excitation methods. In addition, a strategy is proposed for measuring two-dimensional surface temperatures using two gated cameras; the validity was proven for pointwise measurements.

Growth of thin aluminium oxide films on stainless steel by MOCVD at ambient pressure and by using a hot-wall CVD-setup

Abstract: The MOCVD-growth of thin aluminium oxide films on stainless steel substrates was studied by infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Film deposition was performed in a hot-wall CVD-reactor (HWR) at atmospheric pressure. Aluminium acetylacetonate (Al(acac)3) and synthetic air were used as precursors. This approach avoids the usage of an expensive vacuum system and expensive precursors, so low-cost films can be achieved. It turned out that a deposition temperature around 600 K is necessary for film growth, but it can not be increased above 770 K due to the depletion of the precursor. Films deposited at 770 K are multicoloured, well adherent, amorphous, and stable up to 1070 K. They consist mainly of Al and O, although the existence of aluminium hydroxides can not be excluded. Annealing at higher temperatures leads to crystallisation and phase transformations: at 1070 K γ-Al2O3 films resulted and at 1380 K α-Al2O3 was formed. These films are spalling.

Phosphorescence properties of sol–gel derived ruby measured as functions of temperature and Cr3+ content

Abstract: A novel approach for the contactless measurement of surface temperatures is to evaluate the temperature dependent phosphorescence properties of chromium doped aluminium oxide (ruby) coatings, such as phosphorescence intensity, spectral distribution, or the phosphorescence lifetime. However, these properties are also affected by the chromium content in the films. In the present study the phosphorescence lifetimes were studied for the first time as a function of the chromium content. We use a simple sol–gel depositing technique for the preparation of precisely doped ruby coatings in Si(100) substrates. These coatings (Cr-to-Al-ratios y between 0% and 6.8 at. %) are well suited for studying the influence of the chromium concentration on the phosphorescence properties: at room temperature (294 K), the phosphorescence intensity is strongly affected by the chromium doping (maximum at y∼1–1.5%) while the spectrum shifts only slightly with varying chromium content. The phosphorescence lifetime τ at 294 K remains constant with varying Cr3+ content below y∼1.1%, and decreases strongly above y∼1.1%. Thus, ruby doped with y∼1% seems to be most promising as a temperature sensor because it shows the highest phosphorescence intensity and a low variance in the phosphorescence lifetimes. Due to the latter property the temperature evaluation from τ is less affected by imprecise doping. The phosphorescence lifetimes of several sol–gel ruby coatings (y=1.1%) on Si(100) substrates were measured as a function of the temperature to be between 2.7 ms at 294 K and 4 μs at 833 K.

Luminescent probes and sensors for temperature.

Abstract: Temperature (T) is probably the most fundamental parameter in all kinds of science. Respective sensors are widely used in daily life. Besides conventional thermometers, optical sensors are considered to be attractive alternatives for sensing and on-line monitoring of T. This Review article focuses on all kinds of luminescent probes and sensors for measurement of T, and summarizes the recent progress in their design and application formats. The introduction covers the importance of optical probes for T, the origin of their T-dependent spectra, and the various detection modes. This is followed by a survey on (a) molecular probes, (b) nanomaterials, and (c) bulk materials for sensing T. This section will be completed by a discussion of (d) polymeric matrices for immobilizing T-sensitive probes and (e) an overview of the various application formats of T-sensors. The review ends with a discussion on the prospects, challenges, and new directions in the design of optical T-sensitive probes and sensors.

Ordered mesoporous alumina-supported metal oxides

Abstract: The one-pot synthesis of alumina-supported metal oxides via self-assembly of a metal precursor and aluminum isopropoxide in the presence of triblock copolymer (as a structure directing agent) is described in detail for nickel oxide. The resulting mesoporous mixed metal oxides possess p6 mm hexagonal symmetry, well-developed mesoporosity, relatively high BET surface area, large pore widths, and crystalline pore walls. In comparison to pure alumina, nickel aluminum oxide samples exhibited larger mesopores and improved thermal stability. Also, long-range ordering of the aforementioned samples was observed for nickel molar percentages as high as 20%. The generality of the recipe used for the synthesis of mesoporous nickel aluminum oxide was demonstrated by preparation of other alumina-supported metal oxides such as MgO, CaO, TiO 2, and Cr 2O 3. This method represents an important step toward the facile and reproducible synthesis of ordered mesoporous alumina-supported materials for various applications where large and accessible pores with high loading of catalytically active metal oxides are needed.

Trends in luminescence thermometry

Abstract: Following astonishing growth in the last decade, the field of luminescence thermometry has reached the stage of becoming a mature technology. To achieve that goal, further developments should resolve inherent problems and methodological faults to facilitate its widespread use. This perspective presents recent findings in luminescence thermometry, with the aim of providing a guide for the reader to the paths in which this field is currently directed. Besides the well-known temperature read-out techniques, which are outlined and compared in terms of performance, some recently introduced read-out methods have been discussed in more detail. These include intensity ratio measurements that exploit emissions from excited lanthanide levels with large energy differences, dual-excited and time-resolved single-band ratiometric methods, and phase-angle temperature readouts. The necessity for the extension of theoretical models and a careful re-examination of those currently in use are emphasized. Regarding materials, the focus of this perspective is on dual-activated probes for the luminescence intensity ratio (LIR) and transition-metal-ion-activated phosphors for both lifetime and LIR thermometry. Several particularly important applications of luminescence thermometry are presented. These include temperature measurement in catalysis, in situ temperature mapping for microfluidics, thermal history measurement, thermometry at extremely high temperatures, fast temperature transient measurement, low-pressure measurement via upconversion nanoparticle emission intensity ratios, evaluation of the photothermal chirality of noble metal clusters, and luminescence thermometry using mobile devices. Routes for the development of primary luminescence thermometry are discussed in view of the recent redefinition of the kelvin.