Broadband-sensitive up-conversion in Ni2+/Er3+ co-doped Gd2MgTiO6

Ni ²⁺ doped and Ni ²⁺/Er ³⁺ co-doped Gd ₂MgTiO ₆ (GMT) phosphors have been synthesized by conventional high-temperature solid-state reaction method. First-principles calculation and X-ray diffraction analysis proves that Ni ²⁺ ions occupy the Mg ²⁺ sites in the Gd ₂MgTiO ₆ matrix at low Ni ²⁺ doping concentration and begin to occupy Ti ⁴⁺ sites at high Ni ²⁺ doping concentration. The near infrared emissions of Ni ²⁺ ions occupying Mg ²⁺ and Ti ⁴⁺ sites peak at 1344 nm and 1412 nm, respectively, forming a broad near infrared emission band from 1100 nm to 1700 nm. It is found that Ni ²⁺/Er ³⁺ co-doped Gd ₂MgTiO ₆ phosphor is capable to up-convert near infrared photons in the wavelength range of 870–1700 nm to visible 532 nm, 555 nm and 666 nm emission, caused by the energy transfer sensitization process from Ni ²⁺ to Er ³⁺. The Ni ²⁺ and Er ³⁺ concentration dependent up-conversion properties have been investigated and it is found that the Gd ₂MgTiO ₆: 2%Ni ²⁺/5%Er ³⁺ phosphor shows the strongest up-conversion emission, in which the energy transfer efficiencies from the Ni ²⁺ ions occupying Mg ²⁺ and Ti ⁴⁺ sites to the Er ³⁺ ions are 81.5% and 79.3%, respectively. The Gd ₂MgTiO ₆: 2%Ni ²⁺/5%Er ³⁺ phosphor shows yellow emission under the irradiation of 1342 nm and 1550 nm lasers, and green and orange-red emissions under the irradiation of 980 nm and 1064 nm laser, respectively. The broad band excitability and multi-color up-conversion performance of the Ni ²⁺/Er ³⁺ co-doped Gd ₂MgTiO ₆ phosphor suggest that it has wide application prospect in anti-counterfeiting, solar cell efficiency enhancement, infrared detection and so on.