Optical Properties of the (CrF6)3− Complex in A2BMF6:Cr3+ Elpasolite Crystals: Variation with M−F Bond Distance and Hydrostatic Press

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• 作者：Ignacio Herná ; ndez ; Fernando Rodrí ; guez ; Alain Tressaud
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：November 17, 2008
• 年：2008
• 卷：47
• 期：22
• 页码：10288-10298
• 全文大小：407K
• 年卷期：v.47,no.22(November 17, 2008)
• ISSN：1520-510X

文摘

This work investigates the photoluminescence (PL) properties of the Cr³⁺-doped and Cr³⁺-pure fluoroelpasolites along the A₂BMF₆ series and as a function of pressure. In particular, we focus on the variation of the crystal-field spectrum and the associated PL. The results are explained on the basis of the octahedral (CrF₆)³⁻ complex subjected either to external pressure or the internal pressure exerted by different crystal hosts. We have established structural correlations between the crystal-field parameter 10Dq and the Cr−F distance, R_Cr−F, from which we have determined the local structure around the Cr³⁺ impurity, allowing the host material effect on the Cr−F bonds to be studied. As salient features, we show, first, a weak dependence of the first excitation energy, E₁, usually identified as 10Dq, with R_Cr−F as E₁ = KR_Cr−F^−3.3, and, second, an increase of the Stokes shift upon R_Cr−F reduction or with increasing pressure. We associate this unusual behavior with the existence of state mixing among ⁴T_2g(F), ²E_g(G), and ²T_1g(G) states in the first excitation band of Cr³⁺. Finally, high-pressure experiments performed on Rb₂KCrF₆ indicate that the excited-state spin crossover, ²E_g(G) ↔ ⁴T_2g(F), takes place around 7 GPa. The results indicate the suitability of the selected A₂BMF₆:Cr³⁺ elpasolites to establish structural correlations between PL and R_Cr−F.