Rhodamine 6G and its derivatives have been used in wide domain.^[1] Recently, the complexes of rhodamine 6G have also aroused considerable interest.^[2,3] It is found that the rare earth complexes of rhodamine 6G and B have better luminescence properties. As kinds of optical conversion materials, its can be used in growing of plants.
    It is well known that polyethylene (PE) film used in agriculture can keep up the soil temperature and soil moisture to improve the growing conditions of crops, and enable grain, cotton and vegetables to increase yields. Many optical frequency conversion materials doped PE films can change inefficient light in sunlight into efficient light for photosynthesis of crops, promote the maturing of crops and raise the yield of crops.
    In this work, the lanthanum-rhodamine (6G and B) complexes and lanthanum-rhodamine doped polyethylene films were prepared. The experiments of growing seedling and culture of crops and vegetables were carried out in the shed built with doped and undoped polyethylene films.

1 EXPERIMENTAL      
The complexes of rhodamine 6G and rhodamine B with lanthanum were prepared from rhodamine 6G, rhodamine B and lanthanum hydroxide by the rheological phase reaction method.^[4,5] The lanthanum rhodamine 6G (LRG) and lanthanum rhodamine B complexes (LRB) doped PE films were prepared with the same method as preparing PE film. The amount of LRG and LRB doped is 0.2%, respectively. The emission and excitation spectra were obtained with a Shimadzu RF-5000 spectrofluorophotometer. The growing seedling and culture of crops and vegetables were experimented in the shed built with the LRB-doped PE films, and a control experiment with undoped PE film was carried out in the same conditions. The seedbed is 44 m long, 1.33 m wide. The height of the shed is 0.3 m. One experiment area is 10 m long. Two parallel experiments were carried out. In the shed, the thermometers were installed underground (5cm depth) and on the earth's surface, separately. The temperature in the sheds was observed at 8, 14, and 18 per day on time.

2 RESULTS AND DISCUSSION      
The LRB-doped PE films have very strong red luminescence excited by sunlight. The excitation and emission spectra of the LRB-doped PE films are shown in Fig.1. Peaks located at 555 and 580nm are assigned to the emission bands of LRB-doped PE films, respectively. The broad peaks from 470 to590nm are due to the excitation bands. It is showed that the LRG- and LRB-doped PE films can transfer the green light in sunlight to the efficient red light which photosynthesis of crops needs.
    The differences of temperature in the sheds made with two kinds of films are listed in table 1. In the shed with LRB-doped PE film, in sunny day, the temperature of soil surface increased by 1 to 2 degrees, and by 2 to 4.5 degrees 5 cm deep under the mud, compared with that in the shed with undoped PE film. In overcast sky and cloudy day, the temperature increased by 1 to 1.5 degrees in the surface and by 1.5 to 2.5 degrees 5 cm deep under the mud. The difference of soil temperature in the shed with LRB-doped PE film is great in day and night, it is advantageous to the growing of seedlings. In addition, these films have better function of ventilation, and can prevent the seedling from rotting.

Fig.1 The excitation (a) and emission (b) spectra of the LRG (solid line) and LRB (dotted line) doped PE films

* Seeds were sowed on March 28, the rates of sprouting were examined after 15 days

The experimental results of rate of sprouting are listed in table 2. Within 11 days (the seeds were sowed on March 28) the rate of sprouting showed that cotton was 90% higher than that of the undoped PE film, cucumber 9-fold and tomato 10-fold, respectively. Cotton was sowed on April 10, after 6 days the rate of sprouting is 85.5%, it is 10.9% higher than that of the undoped PE film. The growth speed of cotton seedling increased by 23%.
    The output of crop and vegetables cultivated in the same fields after growing seedlings in different films are listed in table 3. The experimental results of cultivation by growing seedlings, the average values of three repeated experiments, indicate that the output of cotton go up more than 10%, winter lettuce 29%, zicaitai about 40%, hot pepper about 60%.

Table 3 The results of the output of crop and vegetables *

REFERENCES   
[1] Soffer B H, Mcfarland B B. Appl Phys Lett, 1967, 10 (10): 266.
[2] Wang H, Xiong R G, Liu C M et al. Inorg Chim Acta, 1997, 254 (1): 183.
[3] Liu C M, Xiong R G, You X Z et al. Acta Chemica Scandinavica, 1998, 52 (7): 883.
[4] Sun J T, Yuan L J, Zhang K L et al. Materials Science and Engineering, 1999, B64: 157.
[5]Zhang K L, Yuan L J, Sun J T et al. J Wuhan Univ, 2000, 46 Special Issue (1): 306.

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