Optical spectra and crystal field calculation for SrB4O7:Sm2+

• Strontium tetraborate doped with divalent samarium has been synthesized.
• Temperature-tunable luminescence of Sm2+ at temperatures has been observed.
• Temperature quenching of the 5D0 multiplet of Sm2+ has been determined.
• The influence of temperature onto thermal shift of lines has been discussed.
• The crystal field calculation of Sm2+ ion has been done.

Undoped and samarium-doped SrB4O7 polycrystalline samples were prepared by a solid state reaction method in air. XRD examination revealed that the undoped sample is consistent with the pure SrB4O7 phase but in samarium-doped sample in addition to the main tetraborate SrB4O7 phase there is a little amount of metaborate. Based on preliminary spectroscopic examination it was ascertained that Sm2+ ions are incorporated without measurable traces of Sm3+ admixture. High resolution luminescence spectra and decay curves of Sm2+ luminescence were measured as a function of temperature in the 5–550 K temperature region. Energies of crystal field components of the 7FJ (J = 1–5) multiplets at 5 K and those of the 5D1 multiplet at 300 K were determined from luminescence spectra and used subsequently as input data for the crystal field calculation. Performed crystal field calculation predicts the energy level scheme for the 4f6 configuration of Sm2+ in SrB4O7 up to 29000 cm−1 and makes it possible to assess the contribution of transitions from the excited states above the 5D1 to luminescence phenomena. Evaluated activation energy Ea ∼4600 cm−1 characterizing a steep decrease of the 5D0 lifetime of Sm2+ between 320 K and 550 K indicates strongly that electronic origin of the lowest energy 7F0 – 4f5d1 vibronic transitions is located around 19200 cm−1, slightly below the 7F0 – 5D3 transition energy.

We report the synthesis and temperature-dependent (5–520 K) studies of SrB4O7 activated with Sm2+ ions. This compound is very efficient red phosphor able to change the color of emitted light due to thermally populated d–f emission. The properties of this compound has been analyzed in the frame of crystal-field model based on its spectroscopic properties.Figure optionsDownload as PowerPoint slide