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The monoclinic Gd 2 O 3 nanoplates phosphor doped with Eu 3+ in the size range ϳ200 to 500 nm and the thickness of several tens of nanometers has been synthesized using the pulp precursor. The particle size and morphology were observed by scanning electron microscopy and transmission electron microscopy. The photoluminescence spectrum is described by the well-known 5 D 0 → 7 F J transition ͑J = 0, 1, 2, etc.͒ of Eu 3+ ions with the strongest emission for J = 2 at 615 and 624 nm. The monoclinic Gd 2 O 3 :Eu nanoplates show a quantum efficiency of 83%, a superior color chromaticity ͑x = 0.662, y = 0.338͒ and a dramatic shorter of decay time compared to the cubic-type bulk Gd 2 O 3 :Eu phosphor.The shape and size of phosphor particles are critical in the fabrication of high quality displays. It was reported that using phosphor with a uniform particle size distribution ͑3-7 m͒ results in the best screen surfaces for both CRT and X-ray screens. 1 In addition, reducing the particle size has been found to result in a higher resolution. 2-4 Therefore, optimizing the particle size distribution will lead to a higher packing density for phosphor layers and thus to a higher resolution. For instance, spherical particles with good distribution result in a high packing density and a small light-scattering coefficient. 5 With the exception of the spherelike phosphor and some nanophosphors, however, there are no reports on a nanoplate phosphor with a narrow size distribution and nonagglomeration for good luminescent characteristics. Gadolinium oxide ͑Gd 2 O 3 ͒ has been extensively used in many different applications. 6,7 It is an effective crystal phosphor exhibiting cathodoluminescence, photoluminescence, and laser action when activated by Eu 3+ or Nd 3+ . 8 This oxide exhibits polymorphic forms, including hexagonal, cubic, and monoclinic forms. The cubic structure is well known as a low-temperature form at ordinary pressures, having a 5 D 0 → 7 F 2 transition of Eu 3+ ͑dominant emission peak at about 612 nm͒. Monoclinic Gd 2 O 3 :Eu luminescence in deeper red wavelength ͑emission at about 620 nm͒ is a candidate for improving color rendering properties. 9 It has been suggested that the monoclinic phase can be obtained by the plasma spray method, where samples are heated above several thousand degrees and then cooled rapidly, and by gas-phase condensation using CO 2 -laser vaporization of pressed and sintered pellets of samples. 10,11 Here, we report on the high-yield impregnation of a pulp with solution-based synthesis of monoclinic nanoplates of Gd 2 O 3 :Eu. ExperimentalThe monoclinic Gd 2 O 3 :Eu nanoplates were prepared as follows. To start, 1.9 g of gadolinium oxide ͑Gd 2 O 3 ͒ was dissolved into 5 mL hydrochloric acid ͑HCl͒ and 3 mL of distilled water, using continuous magnetic stirring then, 10 mL of distilled water was added. The solution was stirred for 10 min. Then, 0.0972 g of Eu͑NO 3 ͒ 3 ·xH 2 O was added, dissolved completely, and soaked in the pulp precursor for 24 h. The different amount of Eu 3+ in a range of 0....