Thermal Relaxation Spectra for Evaluating Luminescence Quantum Efficiency of CASN: Eu2+ Measured by Balanced-Detection Sagnac-Interferometer Photothermal Deflection Spectroscopy

Hiromichi Chima, Naoyuki Shiokawa, Keisuke Seto, Kohsei Takahashi, Naoto Hirosaki, Takayoshi Kobayashi, Eiji Tokunaga*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Highly sensitive broadband photothermal spectroscopy with a white-light lamp as the excitation source was developed by combining a Sagnac interferometer and balanced detection with a photothermal deflection method. A probe beam was split by a birefringent crystal CaCO3 into signal and reference beams with a balanced intensity. This balanced detection enabled the measurement of photoexcited thermal relaxation spectra of materials in the air over the whole visible range in the weak excitation limit 50 mu W/cm(2). The photothermal excitation spectrum of Eu2+-doped CaAlSiN3 phosphors (CASN:Eu2+) with a high luminescent quantum efficiency was measured to be distinctly different from the photoluminescence excitation spectrum which reflects the absorption spectrum, revealing the thermal relaxation mechanism of the phosphor. Assuming a typical non-radiative relaxation from the higher excited states to the lowest excited state and successively to the ground state, it is demonstrated that the photoluminescence efficiency of the phosphors is readily evaluated simply by comparing the photothermal and photoluminescence excitation spectra.

Original languageEnglish
Article number1008
Number of pages13
JournalApplied sciences-Basel
Issue number3
StatePublished - Feb 2020


  • photothermal deflection spectroscopy
  • Sagnac interferometer
  • CASN:Eu2+
  • luminescence quantum efficiency
  • photothermal excitation spectrum
  • photoluminescence excitation spectrum
  • thermal relaxation spectrum
  • balanced detection
  • birefringent crystal CaCO3
  • thermal diffusion length
  • RED
  • BEAM

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