Photon avalanche in Cs2ZrCl6: Os4+

Abstract

The visible (VIS) upconversion luminescence of Cs2ZrCl6: x% Os4+ (x=0.1,1) upon excitation in the near infrared (NIR) is presented and analyzed. The crystals of Cs2ZrCl6: x% Os4+ (x=0.1,1) were synthesized by the Bridgman technique. VIS luminescence around 17 000 cm−1 is induced by NIR excitation between 10 500 and 14 500 cm−1. The three excited states Γ4 (3T1g), Γ5 (1T2g), and Γ1 (1A1g) with 15 K lifetimes of 20 ms, 8 μs, and 4 μs, respectively, in Cs2ZrCl6: 1% Os4+ participate in the upconversion. Excitation at the Γ4 (3T1g)→Γ1 (1A1g) energy shows the typical fingerprints of a photon avalanche. The dynamics of this excitation are calculated with a rate-equation model, and the observed concentration and temperature dependence of the processes are analyzed. The upconversion behavior of Cs2ZrCl6: x% Os4+ (x=0.1,1) is compared with the bromide analog Cs2ZrBr6: 0.2% Os4+.

Theoretical study of the effects of F to Cl chemical substitution on the electronic structure and the luminescence properties of Cs2GeF6:Os4+ and Cs2ZrCl6:Os4+ materials

“…The optical spectrum of the defect center formed when an Os 4+ ion substitutes for a tetravalent cation ͑Ge 4+ or Zr 4+ ͒ in ionic compounds such as Cs 2 GeF 6 and Cs 2 ZrCl 6 corresponds to electronic transitions localized in the ͑OsX 6 ͒ 2− ͑X =F,Cl͒ cluster unit, and is supposed to be governed by the bonding interactions between the impurity Os 4+ and the first neighbor halide anions. These interactions can be adequately described by applying standard high quality quantum mechanical methods to the ͑OsX 6 ͒ 2− cluster.…”

“…As we pointed out before, this chromophore was more widely studied in the past than the fluoride analog. As a result, absorption, 2,7-9,11 luminescence, 2,10 and MCD 9,11 spectra were presented for Os 4+ -doped Cs 2 ZrCl 6 , and the ͑OsCl 6 ͒ 2− chromophore has also been studied in some other crystals 12,15,16,18 and in solution. 20 Most of them focused on the lower energy part of the spectrum, where several groups of sharp lines are found, in close resemblance to the fluoride cluster spectrum.…”

“…In this work we will focus on the properties of two Os 4+ -doped ionic halides, namely, Cs 2 GeF 6 and Cs 2 ZrCl 6 . Both systems have been experimentally investigated recently in relation to their UC properties, together with the related bromide compound, Cs 2 ZrBr 6 .…”

“…Both systems have been experimentally investigated recently in relation to their UC properties, together with the related bromide compound, Cs 2 ZrBr 6 . 2-7 Significant UC is found for the doped chloride, with different characteristics depending on the exciting energy, but no UC is found for the fluoride.…”

“…The optical spectrum and magnetic circular dichroism spectrum of Os 4+ :Cs 2 ZrCl 6 have been studied in the past [8][9][10][11] and the ͑OsCl 6 ͒ 2− chromophore has been studied in other lattices as well [12][13][14][15][16][17][18] and in solution, 19,20 but the studies on the spectrum of ͑OsF 6 ͒ 2− are less numerous. 7,13,21 Both Cs 2 GeF 6 and Cs 2 ZrCl 6 are cubic crystals, with the potassium chloroplatinate structure 22 and the dopant Os 4+ ion which substitutes for a tetravalent cation ͑Ge 4+ or Zr 4+ ͒, in a perfect octahedral coordination. Free Os 4+ has the 5d 4 electronic structure and in octahedral coordination, even in halide compounds, promotes a large ligand field splitting, so that the 3 T 1g ͑t 2g 4 ͒ state becomes the ground state, being followed in energy by predominantly spin singlet t 2g 4 levels.…”