What do we study?

Transparent materials (usually crystals) containing Rare Earth Ions and Transition Metal Ions that luminesce (i.e. emit light) when energy is added to the material. We use lasers to give energy to the material in a very precise manner, and then observe the emitted light. Careful study of this emitted light allows us to gain insights into the physics of what is going on inside the material.

Why study this stuff?

Two reasons. (1) The physics is interesting, and often very complicated. It’s a great challenge! (2) Luminescent crystalline materials are used in many practical applications, such as lasers, lighting (fluorescent and LED), and medical imaging (CAT scans and PET scans). Our current program is focused on materials for use in LED-based lighting, and is sponsored by the National Science Foundation.
For more information, contact John Collins, Physics Department.


In the Laser Spectroscopy Laboratory, we conduct experiments on optical properties of solids, including rare earth ion and transition metal ion-doped insulators and wide band gap semiconductors. Our capabilities include the following measurements:

Absorption, Transmission, and Reflection Measurements

For these measurements we use a Perkin Elmer Lambda 750 UV/VIS/NIR Spectrophotometer, which can measure absorption and transmission between 190 and 3300 nm. With the reflection attachment (with 60 mm integrating sphere and InGaAs detector) we are able to measure diffuse reflectivity between 220 nm and 2500 nm.

Continuous and Time-Resolved Luminescence, Excitation Measurements, and Lifetime Measurements

In a typical emission (luminescence) measurement, one obtains a spectrum showing the wavelength dependence of the intensity of the luminescence from our samples as a function of wavelength in the spectral region between 200 and 2000 nm. In an excitation measurement, one obtains a spectrum of the intensity of the emission at a single wavelength as a function of the wavelength of light exciting the sample. In lifetime measurements, we measure the time dependence of the intensity of the emission from the sample following excitation with a pulsed laser.

The major pieces of equipment include

Light sources:
  • Quantel TDL Laser: This is a Nd-YAG-pumped dye laser with frequency doubling, tripling, and mixing capabilities that allow us to generate 5 ns laser pulses at wavelengths between 200 and 900 nm.
  • Kimmon IK Series He-Cd Laser that produces 15 mW of CW power at 325 nm.
  • Hamamatsu Deuterium/Halogen lamp (model L10290).
  • ILC Technology 300 Watt Xenon Lamp

Dispersion of light:

  • A 0.5 meter Acton SpectraPro 500 Monochromator with resolution of 0.1 nm
  • A Jarrell-Ash 0.25 meter Monochromator

Detection of light:

  • Hamamatsu R-928 photomultiplier tube (200 – 850 nm)
  • Hamamatsu 7459 Photomultiplier tube (190 – 600 nm), mounted in a Model TE327RF Products for Research TE-cooled housing.
  • Hamamatsu TE-cooled InGaAs infrared detector, an amplifier unit (model C1459-03), and a Temperature Controller (model C1103-04).

Other equipment:

  • The following items allow us to vary the sample temperatures from 7K to 300K: Cryo Industries Refrigerator (model REF-2302-204), Sunimoto HC-4A Compressor, and Lake Shore Cryogenics model 335 Temperature Controller.
  • Tektronix Digital Phosphor Oscilloscope, model 4104B (1 GHz bandwidth)
  • Quantum Composers Model 9520 Digital delay pulse generator
  • Newport Model ST 4’ x 10’ Optical Table
  • Various optical components (lenses, mirror, filters, etc.), holders, translation stages, etc.


Luminescence Spectroscopy of Solids

There is an ongoing effort, in collaboration with a group at Boston College, to investigate the luminescent properties of solid-state laser materials, particularly rare earth ion- and transition metal ion-doped insulators. These materials are used for several applications, including lamp phosphors, lasers, display screens (for televisions, computers, etc.), and scintillators (for medical imaging). These materials are useful because, after absorbing energy, they emit light that is characteristic of the atoms that make up the solid. We investigate the processes that take place following the absorption energy. These processes include radiative decay (the emission of light), non-radiative decay (the conversion of energy into heat), and how energy is transferred among the ions in the solid.

Currently our efforts are focused in the following areas:

  • The properties of oxides materials with metal-metal charge transfer states for potential application in solid state lighting devices
  • An investigation into rare-earth ion doped phosphors for use in medical imaging systems
  • Luminescent properties of nanoparticles doped with rare earth and transition metal ions, particularly on the role of surface states and on confinement effects.
  • Upconversion processes as a tool in site-selective spectroscopy.
  • Downconversion as method for increasing the efficiency of solar cells.

In recent years, I have had the pleasure of participating in schools and workshops at the International School of Atomic and Molecular Spectroscopy, which meet in Erice, Sicily during the summers. The topics cover the physics of optical materials, with the most recent workshop (2012) on “New Developments in Inorganic Luminescent Materials. Learn more about the Erice summer schools.

Recent and Current Support

This work is supported by the National Science Foundation under the following grants:

  • National Science Foundation: Award 1126337, MRI: Acquisition of a pulsed laser/detection system for time-resolved studies of molecular complexes
  • National Science Foundation: Award 1105907, RUI: Investigation of metal-to-metal charge transfer states in rare earth ion-doped solids (Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.)
  • OSRAM Sylvania Corp.
  • General Electric Corp.

Recent Student Research

Publications / Presentations
  • Srivastava, M. Jennings, and J. Collins, “The Interconfigurational (4f15d1 to 4f2) Luminescence of Pr3+ in LuPO4, K3Lu(PO4)2 and LiLuSiO4”, Optical Materials 34, 8, ( 2012) 1347-1352.
  • J. Collins, M. Geen, B. Di Bartolo, and M. Bettinelli, Thermal and Concentration Dependence of Cross-Relaxation in Pr-doped YPO4, Journal of Luminescence (2012) http://dx.doi.org/10.1016/j.jlumin.2012.04.027
  • J. Collins, Y. Tsehay, J. Long, P. Boutinaud, R. Boonsin, G. Chadeyron, “Spectroscopy of Pr-doped CaTiO3 under UV excitation”, Meeting of the Electrochemical Society, Honolulu, Hawaii, October 7-12, 2012. (Yohannes Tsehay and Judy Long are Wheaton class of 2014.)
  • T. Bennett and J. Collins, “Luminescence Properties of Pr-Doped Lithium Niobate”, Northeast Undergraduate Research and Development Symposium (NURDS) at the University of New England in Biddeford, ME, March 10-11, 2012. (Tyler Bennett is Wheaton Class of 2012.)
  • J. Collins, M. Bettinelli, P. Boutinaud, M. Geen, B. Di Bartolo, and J. García Sole, “Relaxation via the Intervalence Charge Transfer (IVCT) State in Pr3+-Doped LiNbO3: A Kinetic Approach, to be presented at the International Conference on Luminescence, June 26 – July 1, 2011. (Megan Geen is Wheaton class of 2012)
  • J. Collins, J. Grassetti, K Mishra, D. Hamby, J. McKittrick, J. Tao, S. Shimizu, J Talbot, and B. Di Bartolo, Structural And Optical Properties of ZnO-based Alloys, presented at the Meeting of the Electrochemical Society, Honolulu, HI, October, 2008. ECS Transactions, December, 2008.
  • J. Collins, M. Jennings, J. S. Vartuli, S. J. Duclos, and A. Srivastava, “Luminescence of Pr3+ in LuPO4”, presented at the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, Lyon, France, July, 2008.
  • N. apRoberts Warren, J. Collins, R. Wall, B. Di Bartolo, “Theoretical Studies of Vibronic Transitions of Optically Active Centers in Crystals”, presented at the Spring Meeting of the New England Section of the American Physical Society, Orono, ME, April 2007. (Nick apRoberts-Warren is Wheaton class of2007.)
  • J. Tolson, J. Collins, B. Di Bartolo, “Cross-Relaxation and Diffusion of Energy in Pr-doped Yttrium Silicate”, presented at the Spring Meeting of the New England Section of the American Physical Society, Orono, ME, April 2007. (Jessy Tolson is Wheaton class of 2007.)
  • C. Stuetzle, J. Collins, and M. Gousie, “Stochastic Modeling of Decay Processes in Crystals with Random and non-Random Placement of Ions”, presented at the Spring Meeting of the New England Section of the American Physical Society, Orono, ME, April 2007. (Chris Steutzle is Wheaton class of 2007.)