JOURNAL OF RARE EARTHS, Vol. 33, No. 5, May 2015, P. 486 * Corresponding author: K.A. Koparkar (E-mail: email@example.com; Tel.: +919373487659)
Aldo-keto synthesis effect on Eu3+ fluorescence in YBO3 compared with solid state diffusion
K.A. Koparkar*, N.S. Bajaj, S.K. Omanwar (Department of Physics, Sant Gadge Baba Amravati University, Amravati 444 602, (MH) India)
Received 17 June 2014; revised 6 March 2015
Abstract: The red-orange emitting phosphor YBO3:Eu3+ was prepared by aldo-keto method and solid state diffusion. Aldo-keto method implied to decrease the processing time and heating temperature. The red-orange emitting phosphor was characterized by
X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as emission and excitation photoluminescence spectra recorded at room temperature. The result of aldo-keto method showed that the phosphor YBO3:Eu3+ could be obtained at 900 °C in less time ~60% as compared to solid state diffusion (SSD). The material showed that the strongest emission peak at 595 nm under excitation at 233 nm was only due to forced magnetic dipole 5D0→7F1 transition of Eu3+ ions. Significantly, the emission intensity of YBO3:Eu3+ phosphor prepared by aldo-keto method was relatively higher as compared to that obtained by the solid state diffusion.
Keywords: aldo-keto method; yttria; europium; optical materials; photoluminescence (PL); rare earths
In the past few years, rare earth doped YBO3 phosphor were intensively studied for modern applications in luminescence field such as VUV absorption, plasma display panels, Hg-free fluorescent lamps, etc.[1,2]. Many researchers studied the synthesis of yttrium borate phosphor across the globe, due to the wide band gap and transparence characteristics, trying to enhance their fluorescence intensity. Therefore, researchers tried to use various synthesis routes. Wang et al. synthesized
YBO3:Eu3+ co-doped with some ns2-type ions using solid-state reaction for red phosphor for UV and VUV application. Park et al. synthesized YBO3:Eu3+ phosphor by modified ultrasonic spray pyrolysis under optimum temperature at 1200 ºC for plasma display panel (PDP) application. Jung et al. modified the luminescent properties of YBO3:Eu3+ synthesized through spray pyrolysis with sintering temperature of 1100 ºC for 3 h to enhance luminescent intensity of red phosphor under vacuum ultraviolet excitation. Red-orange emitting
Eu3+ doped YBO3 phosphors have been prepared by solid state synthesis by Balakrishnaiah et al.. In this study, solid state reaction was performed at 1100 ºC and Li doping was used for the charge conjugation to improve intensity of as-synthesized materials. The solid state method was employed for the synthesis of YBO3:Eu3+/
Tb3+. Luminescence material was explored for lamp phosphor application by Gao et al. at relatively low synthesis temperature but with more time. Sato et al. synthesized the YBO3:Ce3+,Tb3+ luminescence materials by solid state reaction at sintering temperature of 1100 ºC.
Dubey et al. studied photoluminescence properties of
YBO3:Eu3+ phosphor under UV radiation synthesized by solid state method with stepwise annealing temperatures of 500, 1000 and 1250 ºC for 1 h.
Inspired from the above discussion, we planned to study the luminescent properties of YBO3:Eu3+ phosphor synthesized using solid state diffusion and aldo-keto methods. To the best of our knowledge and from the literature survey, the synthesis of YBO3:Eu3+ by solid state diffusion method was reported by many researchers and in present work also, which required high temperature.
However, the synthesis through aldo-keto method was processed at low temperature and less time consuming and resulted in high luminescent intensity phosphor, which is the main accomplishment of the present work. 1 Experimental 1.1 Solid state diffusion
The precursor Y2O3 (99.99%, AR) Eu2O3 (99.90%, AR) and H3BO3 (AR) were mixed thoroughly in a mortar.
The resultant mixture was transferred to an alumina crucible and oven dried at 40 ºC. The mixture was heated in a resistive furnace at different elevated temperatures (400, 600, 800 and 1000 ºC) for 2 h at each step with intermittent grindings. The white powder of YBO3:Eu3+ so obtained was used for characterization.
It was well discussed by the researchers that SSD not only needs highly sophisticated equipment but also proK.A. Koparkar et al., Aldo-keto synthesis effect on Eu3+ fluorescence in YBO3 compared with solid state diffusion 487 duces non-uniform particles due to high temperature diffusion. The intermediate grinding required for the fusion of materials produces lots of physical defects and increases the time of reaction. The physical defects produced during the reaction affect the efficiency of phosphor. To overcome the possible drawbacks of solid state diffusion method, we have tried aldo-keto method. The idea about this method originated from the glucose-fructose gel. 1.2 Aldo-keto method
The phosphor YBO3:Eu3+ was prepared for the first time by a novel method of gelation named as aldo-keto gel method, which offers a comparatively low temperature route. The starting chemicals Y2O3 (99.99%,
AR) and Eu2O3 (99.90%, AR) were mixed together in a china clay basin. A small quantity of double distilled water was added and paste was formed. HNO3 was added drop by drop and mixture was heated slowly under observation to 50 ºC till the paste dissolved completely.
The solution was further heated till the excess of acid was boiled off. A small quantity of double distilled water was again added and slowly evaporated to dryness. The resulting powder was Y(NO3)3:Eu, after that soluble solution of H3BO3 (AR) was added. The dried precursor was finally milled. Acetone (2 mol/L, AR) and benzaldehyde (2 mol/L, AR) were added to the nitrate. The pale brownish yellow mixture obtained was stirred continuously and slowly heated to 130 ºC. The mixture became dark brownish yellow and then dark reddish brown between 80 to 120 ºC with evolution of brownish gases.