Introduction

What is LumiSpy

LumiSpy is an open-source python library aimed at helping with the analysis of luminescence spectroscopy data. The development started mainly with photoluminescence (PL), cathodoluminescence (CL), electroluminescence (EL) and Raman spectroscopy in mind. Besides the standard continuous-excitation spectral data, the idea is to provide tools also for the analysis of time-resolved (transient) measurements. However, LumiSpy may prove useful also for other optical measurements, such as absorption or transmission spectroscopy, scanning optical near field miscroscopy (SNOM), as well as fourier-transform infrared spectroscopy (FTIR).

LumiSpy is an extension to the python package HyperSpy that facilitates hyperspectral data analysis, i.e. maps or linescans where a spectrum is collected at each pixel. Or more general, multidimensional datasets that can be described as multidimensional arrays of a given signal, as illustrated by the following figure:

To facilitate working with these datasets, HyperSpy distinguishes between navigation and signal dimensions that can be addressed separately and thus, for example, operations on a single spectrum can be easily mapped to a whole dataset.

Notable features that HyperSpy provides are:

• base signal classes for the handling of (multidimensional) spectral data,

• the necessary tools for loading various data file formats,

• analytical tools that exploit the multidimensionality of datasets,

• a user-friendly and powerful framework for model fitting that provides many standard functions and can be easily extended to custom ones,

• machine learning algorithms that can be useful, e.g. for denoising data,

• efficient handling of big datasets,

• functions for data visualization both to evaluate datasets during the analysis and provide interactive operation for certain functions, as well as for plotting of data,

• extracting subsets of data from multidimensional datasets via regions of interest and a powerful numpy-style indexing mechanism,

• handling of non-uniform data axes (introduced in the v1.7 release).

LumiSpy provides in particular:

• additional Signal types specifically for luminescence spectra and transients,

• transformation to non-uniform signal axes for use of other common units, such as eV (electron volt) and wavenumbers (Raman shift),

• additional signal tools such as data normalization and scaling,

• various utility functions useful in luminescence spectroscopy data analysis, such as joining multiple spectra along the signal axis, unit conversion, etc.

LumiSpy should facilitate an easy and reproducible analysis of single spectra or spectral images.

Signal types

As an extension to HyperSpy, LumiSpy provides several signal types extending the base classes available in HyperSpy. When the LumiSpy library is installed, these additional signal types are directly available to HyperSpy. To print all available specialised hyperspy.signal.BaseSignal subclasses installed in your system call the hyperspy.utils.print_known_signal_types() function:

>>> import hyperspy.api as hs
>>> hs.print_known_signal_types()

The different subclasses are characterized by the signal_type metadata attribute. Some additional properties are summarized in the table below. Depending on the use case, certain functions will only be available for some signal types (or inheriting) signal types.

LumiSpy subclasses and their basic attributes.

BaseSignal subclass	signal_dimension	signal_type	dtype	aliases
LumiSpectrum	1	Luminescence	real	LumiSpectrum, LuminescenceSpectrum
CLSpectrum	1	CL	real	CLSpectrum, cathodoluminescence
CLSEMSpectrum	1	CL_SEM	real	CLSEM, cathodoluminescence SEM
CLSTEMSpectrum	1	CL_STEM	real	CLSTEM, cathodoluminescence STEM
ELSpectrum	1	EL	real	ELSpectrum, electroluminescence
PLSpectrum	1	PL	real	PLSpectrum, photoluminescence
LumiTransient	1	Transient	real	TRLumi, TR luminescence, time-resolved luminescence
LumiTransientSpectrum	2	TransientSpec	real	TRLumiSpec, TR luminescence spectrum, time-resolved luminescence spectrum

The hierarchy of the LumiSpy signal types and their inheritance from HyperSpy is summarized in the following diagram:

└── hyperspy.signal.BaseSignal

├── hyperspy._signals.signal1d.Signal1D

│ └── LumiSpectrum

│ │ ├── CLSpectrum

│ │ │ ├── CLSEMSpectrum

│ │ │ └── CLSTEMSpectrum

│ │ ├── ELSpectrum

│ │ └── PLSpectrum

│ └── LumiTransient

└── hyperspy.signal.Signal2D

└── LumiTransientSpectrum

Where are we heading?

LumiSpy is under active development, and as a user-driven project, we welcome contributions (see Contributing) to the code and documentation, but also bug reports and feature requests from any users. Don’t hesitate to join the discussions!

Currrently, we have implemented the base functionality that extends HyperSpy’s capabilities to additional signal classes. In the near future, the following functions should be developed:

• handling of transient (time-resolved) data,

• reading of common PL data formats (see Supported formats of RosettaSciIO),

• more dedicated analysis functionalities,

• …