Powder samples of Cr³⁺-doped δ*-Al₂O₃ with particles sizes of 10–70 nm were obtained by combustion method. It is shown for the first time that Cr³⁺ ions in the δ*-Al₂O₃ occupy octahedral sites in the bulk and at the surface of the nanosized particles. The photoluminescence spectra of Cr³⁺ in δ*-Al₂O₃ consist of several relatively narrow lines (R-lines luminescence) in the 680–720 nm range, which are due to the ²E_g→ ⁴A_2g transitions. The local structure around Cr³⁺ ions inside the nanoparticles is shown to differ from that of Cr³⁺ located in the surface layer, which results in essential differences in the full width at half maximum values (14 cm⁻¹ vs. 39 cm⁻¹ at 77 K) and in red shift of the R-lines with increasing temperature from 77 to 293 K (20 cm⁻¹ vs. ~11 cm⁻¹). It was found that the Cr³⁺-doped δ*-Al₂O₃ exhibits some striking features, including an unexpectedly high crystal-field strength at the interior Cr³⁺ site and an unusually high concentration of surface Cr³⁺ centers. Possible reasons for these features are discussed. The results obtained are anticipated to be useful for the monitoring of processes involved in the preparation of ceramics and composites based on Al₂O₃:Cr³⁺.

Cr ³⁺掺杂的δ*-Al ₂ O ₃粉末样品通过燃烧法获得，粒径为10-70 nm。首次表明δ*-Al ₂ O ₃中的Cr ³⁺离子占据纳米颗粒的本体和表面的八面体位点。δ*-Al ₂ O ₃中Cr ³⁺的光致发光光谱由680-720 nm 范围内的几条相对较窄的谱线（R 谱线发光）组成，这是由于² E _g → ⁴ A _2g跃迁造成的。Cr ³⁺周围的局部结构纳米粒子内部的离子与位于表面层中的 Cr ^{3+ 离子}不同，这导致半高全宽（14 cm ^-1对 77 K 时的39 cm ^-1）和随着温度从 77 增加到 293 K（20 cm ^-1对 ~11 cm ^-1），R 线的红移。发现 Cr ³⁺掺杂的 δ*-Al ₂ O ₃表现出一些引人注目的特征，包括在内部 Cr ³⁺位点处出乎意料的高晶体场强度和异常高浓度的表面 Cr ³⁺中心。讨论了这些功能的可能原因。预计获得的结果可用于监测基于 Al ₂ O ₃ :Cr ³⁺的陶瓷和复合材料的制备过程。