Common mistakes in luminescence analysis

Abstract

Abstract. Luminescence techniques are powerful and sensitive probes to study imperfections, impurities and modifications of insulating materials. They are used in a wide range of disciplines from condensed matter physics to archaeology and mineralogy and the methods have developed over nearly a century. Early equipment was often not quantitative and data were collected in formats that were difficult to process and manipulate, and so signals were frequently presented in terms of the initial signals without corrections for equipment spectral sensitivity. Unfortunately not only did this distort the information but often it resulted in incorrect interpretations. Further, the incorrect data handling has persisted into modern usage both by physicists and those in other fields who merely use luminescence as a sensitive technique. Several main types of problem are considered. These include temperature errors in thermoluminescence dosimetry; subtleties in the signal intensity corrections for the responses of both the spectrometer and detectors; grating polarization effects; sample anisotropy; and common errors in spectral deconvolution, especially failure to transform from wavelength to energy plots. IntroductionLuminescence signals provide information on relaxation processes in both inorganic and biological materials and the photon energy of the transition is primarily defined by the electronic structure around the emission site. Subtle variations in the structure will then influence the transition energy and excited state lifetime. Such variations have been successfully used to track changes over volumes as large as 50 neighbouring shells. Luminescence is therefore a powerful probe of defect structures in insulators, as well as responding to impurities, phase changes and distortions such as those caused by stress or nanoparticle inclusions. Equally, the changes induced by local distortion make luminescence a useful probe to distinguish between healthy and diseased biological material and it is used in the emerging field of Optical Biopsy. Luminescence signals have been studied for more than a century with techniques from simple visual observation to black and white or colour photography. By the 1960s more quantitative detectors, such as photomultiplier tubes became available. However the spectral information was generally displayed on a chart recording as a monochromator swept through the wavelength range of the system. Such raw data were then published and used as the basis for discussion and interpretation of the luminescence. For some applications this was acceptable, for example in mineralogical applications changes in spectra revealed different component materials and the presence of rare earth ions were easily identified by characteristic line spectra. It must be recalled that in the 1960s attempts to remove the background dark current, and then scale the signals to correct for the transmission efficiency of the monochromator and sensitivity of the PM tube involved tedious manual processing (N.B. on line computer...

Quantitative assessment of constitutive G protein-coupled receptor activity with BRET-based G protein biosensors

“…4B ). The former include emission wavelength-dependent sensitivities of photon-collecting, -counting and - converting (into electrical signals) optical detectors in commercially available luminescence plate readers ( 45 ). For instance, a higher sensitivity in detecting increases in emission intensity in the cpVenus channel would artificially elevate the sensor’s BRET ratio over increasing relative luminescence units (e.g.…”

Spectroscopic Properties of Si-nc in SiOx Films Using HFCVD

“…Figure 9 depicts the deconvolution of the photoluminescent spectrum of the D2’ film. To perform the deconvolution and in order to avoid common errors reported in the photoluminescence analysis, the spectra were deconvolved using the PL intensity-energy differential versus energy [ 41 ].…”

Spectroscopic and Microscopic Correlation of SRO-HFCVD Films on Quartz and Silicon

“…The HRTEM On the other hand, Figures 9 and 10 show the photoluminescent (PL) emission spectra of the single-layer SRO films and Figures 11 and 12 show the twofold-layers SRO films, both on Quartz and Silicon substrates, as-G and with HT. In the graphs of Figure 9, 10, 11, and 12 a,b, are showing the PL spectra as they were just obtained to compare the intensity PL as-G and with HT, while in the insets of Figure 9, 10, 11, and 12c,d, the spectra were plotted according to the Energy I (E) dE versus the energy ratio given by Y. Wang and PD Townsend [32], to obtain the graphs in terms of energy and With the experimental values of the Eg opt it is possible to estimate the Si-ncs size (d = Si-ncs diameter) using Equation (2) [28], thus the calculated diameters are shown in Table 4 together with the corresponding Eg opt of each film.…”

“…On the other hand, Figures 9 and 10 show the photoluminescent (PL) emission spectra of the single-layer SRO films and Figures 11 and 12 show the twofold-layers SRO films, both on Quartz and Silicon substrates, as-G and with HT. In the graphs of Figures 9, 10, 11 and 12a,b, are showing the PL spectra as they were just obtained to compare the intensity PL as-G and with HT, while in the insets of Figures 9, 10, 11 and 12c,d, the spectra were plotted according to the Energy I (E) dE versus the energy ratio given by Y. Wang and PD Townsend [32], to obtain the graphs in terms of energy and perform the deconvolutions that determine the most intense energy peaks and thus relate them with the emission mechanisms. It is emphasized that the evolution of the peaks in the PL spectra both in their intensity and in the wavelength shifted from their position is attributed mainly to the heat-treated carried out at 1100 • C for 60 min in N 2 atmosphere.…”