The riddle of orange\u2013red luminescence in Bismuth-doped silica glasses

Oleksii V Laguta,Igor M Razdobreev

doi:10.1038/s41598-021-87290-z

Abstract

For over the past two decades it has been believed that the intense orange-red photoluminescence in Bismuth-doped materials originates from Bi^{2+} ions. Based on the results from magnetic circular polarization experiments, we demonstrate that this hypothesis fails for Bismuth-doped silica glasses. Our findings contradict the generally accepted statement that the orange-red luminescence arises from ^{2}P_{3/2}(1)rightarrow^{2}P_{1/2} transition in a divalent Bismuth ion. The degree of magnetic circular polarization of this luminescence exhibits non-monotonic temperature and field dependencies, as well as sign reversal. This complex behaviour cannot be explained under the assumption of a single Bi^{2+} ion. The detailed analysis enables us to construct a consistent diagram of energy levels involved in the magneto-optical experiments and propose a new interpretation of the nature of orange-red luminescence in Bismuth-doped silica glass. A centre responsible for this notorious photoluminescence must be an even-electron system with an integer total spin, presumably a dimer of Bismuth ions or a complex consisting of Bi^{2+} and an oxygen vacancy.

Highlights

For over the past two decades it has been believed that the intense orange-red photoluminescence in Bismuth-doped materials originates from Bi2+ ions
The orange-red photoluminescence (ORPL) in Bismuth-doped materials has been noted since the work of Lecoq de Boisbaudran[1], who observed this luminescence in MSO4:Bi (M = Zn, Cd and Pb) sulfates which were subjected to the electrical discharge
In the present paper, we report on the measurements of magnetic circular polarization of luminescence (MCPL) in bulk Bismuth-doped silica glass

Summary

Introduction

For over the past two decades it has been believed that the intense orange-red photoluminescence in Bismuth-doped materials originates from Bi2+ ions. The EPR signal in these single crystals appears only after irradiation (X-rays, mercury or xenon lamps) at low temperatures (77 – 100 K) and it completely disappears at room temperature Both compounds exhibit intrinsic ORPL, which is observed in these materials under excitation in the range of 340 – 370 nm (for PbWO4 see, for instance ref.18), while the appearance of new additional photoluminescence (PL) or absorption bands directly connected to Bi2+ ions was not reported and remains questionable. Another class of materials that exhibit ORPL related to Bismuth doping are silica-based glasses. Despite this technological progress, the nature of NIR PL and lasing centres continues to be d iscussed[32,33,34]

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Conclusion