| Popis: |
Plants in greenhouses are grown under special lighting conditions, i.e. when partially or completely artificial lighting is used. For this purpose, various lamps are used - xenon, high or low pressure sodium, mercury, LED, etc. Recent studies have shown that LED lamps can achieve about 60 % more efficiency in greenhouse lighting than sodium lamps. The increased energy efficiency of LED lamps (phyto-lamps) is associated with the coincidence of their emission bands with the spectra of photosynthetic active radiation. The simplest phyto-lamps are devices consisting of several blue and red light LEDs (phyto-LEDs). A significant disadvantage of red LEDs those are based on the semiconductor structures is their cost, which is much higher than that of blue phyto-LEDs. One of the ways to reduce the price of red LEDs can be their elaboration on the basis of an InGaN semiconductor structure (chip) with a blue light emission, with a deposited layer of an inorganic phosphor. Phosphors with a red emission can be created on the basis of oxide materials with ions of transition or rare earth metals, such as Pr3+. The advantage of praseodymium over transition element ions is that the main absorption bands of Pr3+ ions in the visible region located in the range of 430–490 nm, namely in the emission region of blue LEDs. The position of these bands weakly depends on the type of crystalline or glass matrix. In this work, luminescent coatings based on KBi(MoO4)2 and K2Bi(PO4)(MoO4) crystals doped with Pr3+ ions are considered. The coating on the LED was carried out using a polymer - cyanoacrylate glue. It has been found that the polymer used weakly absorbs LED radiation and does not exhibit significant luminescence in the visible region upon excitation at 446 nm. For a coating based on K2Bi0.99Pr0.01(PO4)(MoO4), it was shown that, in terms of the position of the oxide luminescence bands, it agrees well with the red absorption band of chlorophyll b and with weak absorption bands of chlorophyll in the range of 590–620 nm. However, the efficiency of blue into red light converting for this coating is rather low. Better results can be achieved with KBi0.9Pr0.1(MoO4)2, which has a better correlation with chlorophyll’s absorption bands, as well as a higher blue-to-red conversion efficiency. In our opinion, by varying the content of praseodymium in KBi1-xPrx(MoO4)2 and optimizing the deposition method, it is possible to increase the efficiency of such luminescent coatings for the development of phyto-LEDs. |
