Study of effects of rare earth impurities on structure of matrix emission of the lead tungstate crystals

The paper reports study of complex structure of matrix emission of undoped and RE-doped PbWO4 crystals. Decomposition of the spectra shows contributions of five components at 410, 485, 520, 565, 635 nm in emission of all the investigated samples. Their relative contributions depend on RE doping. Observed effects of RE doping are the same for the crystals with different RE impurities. Structures of luminescent centres are discussed taking into account studied effects of the impurity RE ions on spectral characteristics of the matrix emission

Modeling and Analysis of Effective Ways for Improving the Reliability of Second-hand Products Sold with Warranty

Often, customers are uncertain about the performance and durability of the used/second-hand products. The warranties play an important role in reassuring the buyer. Offering the warranty implies that the dealer incurs additional costs to service any claims made by the customers. Reducing warranty costs is an issue of great interest to dealers. One way of improving the reliability and reducing the warranty servicing cost for second-hand items is through actions such as overhaul and upgrade which are carried out by the dealer or a third party. Improving actions allow the dealer to offer better warranty terms and to sell the item at a higher price. This paper deals with two effective approaches (virtual age approach and screening test approach) to decide on the reliability improvement strategies for second-hand products sold under various warranty policies (failure-free, rebate warranty, and a combination of free replacement and lump sum). A numerical example illustrates that from a dealer’s point of view, it is beneficial to carry out an improvement action only if the reduction in the warranty servicing cost is greater than the extra cost incurred due to this improvement action

Doubly geometric processes and applications

The geometric process has attracted extensive research attention from authors in reliability mathematics since its introduction. However, it possesses some limitations, which include that: (1) it can merely model stochastically increasing or decreasing inter-arrival times of recurrent event processes, and (2) it cannot model recurrent event processes where the inter-arrival time distributions have varying shape parameters. Those limitations may prevent it from a wider application in the real world. In this paper, we extend the geometric process to a new process, the doubly geometric process, which overcomes the above two limitations. Probability properties are derived and two methods of parameter estimation are given. Application of the proposed model is presented: one is on fitting warranty claim data and the other is to compare the performance of the doubly geometric process with the performance of other widely used models in fitting real world datasets, based on the corrected Akaike information criterion

Structure of Centers of Matrix Emission of the Undoped and RE-Doped Scheelite-Type Lead Tungstate Crystals

The paper reports the investigation of a structure of luminescence spectra of PbWO4 (PWO) crystals. The doping of the samples with rare earth (RE) impurities is used in order to obtain more information about the composition of spectra of the PWO matrix emission and the structure of its luminescence centers. The decomposition of the emission spectra onto individual bands has shown that 5 bands contribute to the total spectra of all the undoped and RE-doped samples at 10 K. The maxima of the obtained bands are 1.95, 2.2, 2.45, 2.7, and 3.0 eV. Effects of the RE-doping and the annealing on relative intensities of these bands are considered. The nature of luminescence and the structure of the centers involved in the excitation and emission processes responsible for each of the separated bands are discussed

Luminescent Spectroscopy of the Yb³⁺ Ions in the PbWO₄ Crystal

Luminescent properties of the PbWO₄ crystals undoped and doped with the Yb³⁺ ions were studied. Emission spectra of the crystals consist of broadband matrix emission in 350-750 nm spectral range and narrow spectral lines caused by inner electron transitions in the impurity Yb³⁺ ions in 920-1040 nm spectral range. Analysis of the linear spectra has shown that Yb³⁺ ions form two types of emission centres. Structures of these centers are discussed taking into account possibility of the impurity ions incorporation in different positions (Pb and W sites) in the crystal lattice. Effects of the Yb³⁺ impurities on matrix emission were studied. Transfer of excitation energy from matrix to the Yb³⁺ decreases intensity of the red band of matrix emission. The Yb³⁺ impurities also increase intensity of the blue band by formation of additional Yb³⁺-induced channel of excitation of this band. The described effects of Yb³⁺ doping on properties of matrix emission are caused by the Yb³⁺ ions arranged in Pb positions

Luminescent Spectroscopy of the Yb3+^{3+} Ions in the PbWO4_4 Crystal

Luminescent properties of the PbWO$_4$ crystals undoped and doped with the Yb$^{3+}$ ions were studied. Emission spectra of the crystals consist of broadband matrix emission in 350–750 nm spectral range and narrow spectral lines caused by inner electron transitions in the impurity Yb$^{3+}$ ions in 920–1040 nm spectral range. Analysisof the linear spectra has shown that Yb$^{3+}$ ions form two types of emission centres. Structures of these centers are discussed taking into account possibility of the impurity ions incorporation in different positions (Pb and W sites) in the crystal lattice. Effects of the Yb$^{3+}$ impurities on matrix emission were studied. Transfer of excitation energy from matrix to the Yb$^{3+}$ decreases intensity of the red band of matrix emission. The Yb$^{3+}$ impurities also increase intensity of the blue band by formation of additional Yb$^{3+}$-induced channel of excitation of this band. The described effects of Yb$^{3+}$ doping on properties of matrix emission are caused by the Yb$^{3+}$ ions arranged inPb positions