Cold white light generation from hafnium oxide films activated with Ce 3+ , Tb 3+ , and Mn 2+ ions

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Enrique A Departamento de Fı´sica, Universidad de Sonora (UNISON), Hermosillo, Sonora 83000, Me´xico

Adolfo Speghini DiSTeMeV, Universita` di Verona, and INSTM, UdR Verona, I-37029 San Floriano, Verona, Italy

Ciro Falcony Centro de Investigacio´n y de Estudio Avanzados del IPN, Departamento de Fı´sica, 07000 Me´xico, D.F., Me´xico

Ulises Caldin˜oa) Departamento de Fı´sica, Universidad Auto´noma Metropolitana-Iztapalapa, 09340 Me´xico, D.F., Me´xico (Received 15 September 2009; accepted 9 December 2009)

Hafnium oxide films doubly doped with CeCl3 and TbCl3 and triply doped with CeCl3, TbCl3, and MnCl2 were deposited at 300  C with the ultrasonic spray pyrolysis technique. The green and yellow emissions of Tb3+ ions and the yellow-red emission of Mn2+ ions can be generated upon ultraviolet (UV) excitation via a nonradiative energy transfer from Ce3+ to Tb3+ and Ce3+ to Mn2+. In the doubly doped film Ce3+ ! Tb3+ energy transfer via an electric dipole–quadrupole interaction appears to be the most probable transfer mechanism; the efficiency of this transfer is about 81% upon excitation at 270 nm. In the HfO2 films activated with Ce3+, Tb3+, and Mn2+ the efficiency of energy transfer from Ce3+ to Tb3+ and Mn2+ ions is enhanced by increasing the Mn2+ concentration, up to about 76% for the film with the highest manganese content (1.6 at.%). In addition, it is demonstrated that these triply doped films can generate cold white light emission upon excitation at 270 nm (peak emission wave length of an AlGaN/GaN-based LEDs).

I. INTRODUCTION

The development of new phosphors that can be pumped through ultraviolet (UV) light emitting diodes (LEDs) has been the subject of intense research during recent decades because of the necessity of increasing the efficiency in white light emitting solid-state devices for application in new generation of lighting lamps.1 White light generation through the simultaneous emission of blue, green, and red emitting centers upon UV excitation was reported for the first time in borate-based glasses containing Ce3+, Tb3+, and Mn2+ as activators.2 Ce3+ ions exhibit broad absorption bands in the UV, so that they can be excited by LEDs.3 The advantage of using commercial diodes is their low-energy consumption, longevity, and reduced size. The intense broad-band absorption and luminescence of Ce3+ ions is a consequence of their 4f–5d parity allowed electric dipole transitions. In codoped materials Ce3+ ions act as good sensitizers, so a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0065

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http://journals.cambridge.org

J. Mater. Res., Vol. 25, No. 3, Mar 2010 Downloaded: 11 Apr 2015

that they can transfer a part of their excitation energy to activator ions such as Tb3+,2–5 Mn2+,2,3,6–11 and Eu2+.12,13 Tb3+ ions in solids show allowed intense 4f8 ! 4f75d absorptions in the UV and forbidden 4f8 ! 4f8 absorptions at lower energy (near UV). On the other hand, Mn2+ ions in solids show forbidden 3d ! 3d absorption transitions. Nevertheless, both Tb3+ and

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